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Diesel engines are used in automotive and stationary  applications. The main problem with diesel engines is emissions  of nitrogen oxides (NOx) and particulates. In order to minimize  the emissions, it is necessary to design the diesel engine with  better in-cylinder flow (air-fuel mixing) and combustion  process. Computational Fluid Dynamics (CFD) simulation  helps to understand the Diesel engine temperature distribution  and NOx species concentrations with respect to time. A small  direct injection (DI) engine was chosen for the study. CFD simulation results were compared with that of engine emission tests. Results were found to be in agreement with NOx  emissions. This paper also presents the simulation results of  direct injection diesel engine in-cylinder flow (air-fuel mixing)  and combustion.

Introduction The issue of noise pollution is one of the concerns of most societies and industries because of their relationship to the environmental comfort of life or work of people are paying attention. The Aero-acoustics not only because of government regulations on the noise pollution, but also due to the increasing demand of the people's living standards and create a safe environment for farm animals is considered important. At the same time, products with high aero-acoustic performance will attract a lot of customers, which is in the interest of the global economy. Reducing current noise is often accompanied by a reduction in energy costs, resulting in durability of structures and improved product quality. Materials and Methods Sound measurements were carried out at the wind tunnel in Tabriz Tractor Engineers Company. Using the measurements performed by the instrument, the sound levels were measured at different periods of the fan. In many practical applications that include turbulent flow, no noise has any specific tone and the sound energy is continuously distributed over a wide range of frequencies. In cases where broadband noise is present, statistical disturbance values easily calculated from the RANS equations can be used in conjunction with semi-experimental correlations and audio coordination to reveal some broadband noise sources. Based on the problem, the boundary condition is the type of "input velocity" for the input and "output pressure" for the output. It was also used to move the mesh to apply the rotary motion of the fan. The thermodynamic conditions at these boundaries should be considered. Results and Discussion The accuracy of the simulation results data was verified with the measured data. In the laboratory results, the audio level is accompanied by an audio environment and an inverter and a belt that is about 15 db. With this in mind, the simulation results had a good agreement with experimental results. The velocity is a critical parameter in fan-related discussions. In the upper part of the fan, the speed of the air increases as the fan sucks, and this speed will increase as the fan approaches. In the second part, which includes the fan, for speeding objects, the speed will increase as the radius increases (due to the constant rotational speed), so the maximum speed will be at the tip of the blades. In the lower part of the fan, the speed will decrease as the fan impact decreases on the air molecules as well as the boundary layer behavior near the walls. As the speed and intensity of the turbulence are higher at the tip of the blades, hence the kinetic energy of these regions must also be higher. The kinetic energy of the turbulence in these areas is the highest. At the bottom of the fan, it is also observed that the kinetic energy of the turbulence has been relatively high, due to the existence of flow vortices that emerge from the fan period and the presence of positive and negative pressure (negative pressure due to suction of the fan center). The high pressure difference on both sides of the fluid particles causes a rotating flow in the particles, which affects the adjacent particles and causes vortex formation. Conclusion The results showed that the numerical acoustic evaluation simulates the performance of the broadband band with good results and has good agreement with the effects of the current on the noise. Increasing the recognition of the factors and their effects on the fan noise level can help to reduce the noise effects of turbo-machines. Using numerical simulations in predicting and reducing noise, in addition to time saving, dramatically reduces costs by using direct methods and mechanical design physically. With regard to all aspects and calculations, it can be concluded that acoustic numerical simulation and broadband noise model have a good ability to analyze noise in fans and rotary machines.

Introduction Greenhouse cultivation is the popular intensive kind of crop production with a yield per cultivated unit area more than 10 times higher compared to field crops. Greenhouse production requires the use of large amounts of energy, water, and pesticides and it usually generates huge quantities of wastes to be disposed of it. Investment, labor, and energy costs per unit area are much higher in the greenhouse industry than in any other agricultural sectors. Sustainable greenhouse systems, socially supportive, commercially competitive, and environmentally sound, depend on cultivation techniques, equipment management, and constructive materials that aim to reduce agrochemicals, energy and water consumption as well as waste generation. The management of the greenhouse environment is depending on temperature manipulation. Temperature manipulation is critical to influencing plant growth, quality, and morphology and so is a major strategy in the environmental modification of crops. Heterogeneous indoor microclimate of a greenhouse has long become a matter of concern in many studies. It is believed to be unfavorable for crop growth, which damages crop activity, particularly transpiration and photosynthesis, one of the major causes of non-uniform production and quality. Since early and conventional methods are not sufficient to evaluate microclimate variables inside a greenhouse, Computational Fluid Dynamics (CFD) approach was applied for better and more accurate results. CFD is an effective numerical analysis technique to predict the distribution of the climatic variables inside cultivation facilities. Numerous studies have focused on the internal temperature, humidity, solar radiation, and airflow inside multiple cultivation facilities. For example, the CFD method was used to simulate natural ventilation for agricultural buildings and improve crop production systems. The CFD simulation and evaluation models could be applied for evaluation of the inside situation and temperature in greenhouses. Thermal and water vapor transfer is influenced by the openings of greenhouses in the CFD simulation. The CFD model was developed to predict the distribution of temperature, water vapor, and CO 2 occurring in a Venlo-type semi-closed glass greenhouse equipped with air conditioners. Based on the above literature, this research aims to evaluate the energy flow and modeling of an un-even semi-buried greenhouse using external and internal variables and numerical solutions by the CFD method. Materials and Methods In this study, Computational Fluid Dynamic (CFD) solution was applied to evaluate the inside environment of a semi-double glass greenhouse with an east-west location. This greenhouse has a special structure that is used in very hot or very cold areas due to its depth of more than one meter below the ground. The greenhouse has an area of 38m 2 and an air volume of 78.8m 3 . The temperature and humidity data were collected from inside and outside the greenhouse by temperature sensors (SHT 11 model made by CMOS USA). Irradiation data were collected inside the greenhouse, on level ground, by the TES132 radiometer. Results and Discussion In this study, the CFD method was used for a model solution with ANSYS Fluent version 2020R2 software. To evaluate the predictive capability of the model and its optimization, the comparison between actual (ya) and predicted values (yp) was used. Three criteria of RMSE, MAPE, and R 2 were also used to evaluate the accuracy of the final model. The results showed that the dynamic model can accurately estimate the temperature of the air inside the greenhouse at a height of 1 m (R 2 = 0.987, MAPE = 2.17%) and 2 m (R 2 = 0.987, MAPE = 2.28%) from the floor. The results of energy flow showed that this greenhouse transfers 6779.4.4 kJ of accumulated thermal energy to the ground during the experiment. Conclusion In the present study, the computational fluid dynamics method was used to simulate the internal conditions of an un-even semi-buried greenhouse with external and internal variables including temperature and solar radiation. The results showed that this greenhouse structure is able to transfer part of the increase in temperature caused by sunlight to the soil depth (104.214 kJm -2 heat through the floor, 178.443 kJm -2 through the north wall and 113.757 kJm -2 through the south wall). By increasing the thermal conductivity of the inner surface of the greenhouse, the heat flux to the depth of the soil can be increased.

Introduction Cyclones are widely used to separate solid particles from the fluid phase. Due to the ease of construction, low running costs, and hard-working conditions at high temperatures, people's interest in using cyclones is increasing day by day. Engineers are generally interested in two parameters to perform a complete evaluation of the design and operation of a cyclone. These parameters are the particle collecting efficiency and the pressure drop inside the cyclone. The precise prediction of the pressure drop in cyclone is very important which it is directly related to operating costs. Computational Fluid Dynamics (CFD) is a diversified tool for predicting flow behavior in a wide range of design and operational conditions. Numerical solution of Navier-Stokes equations is the basis of all CFD techniques, which is the result of fast computer upgrades and a better understanding of the numerical resolution of turbulence. Materials and Methods Regarding preliminary experimental tests and understanding the fluid flow, the flow rate of 0.08 kg s -1 was selected as the flow rate. Six levels of inlet velocities 10, 12, 14, 16, 18, and 20 m s -1 were selected for understanding the effect of inlet velocity on the cyclone performance. The measurements were carried out using a hot-air anemometer (TSI-8484model with a resolution of 0.07 m s -1 and an operating range of 0.125 to 50 m s -1 ), and a pressure differential meter instrument (CPE310s-KIMO model) with an accuracy of 0.1 Pa. The region is discretized as a finite volume in a set, called the region grid or mesh after discretization. For incompressible fluids, pressure-based and density-based solvers are used, respectively. Regarding the velocity of the material entering the cyclone and low Mach number, a pressure-based solver could be used in this study. The shear stress transport model (SST) is a modified version of the k-ω 2-equation model. This model combines the two turbulence k-ω and k-ε models. The Lagrangian discrete phase model in Ansys Fluent follows to the Euler-Lagrangian model. Defining the best type of boundary condition is important for solving the problem and extracting solving fields. The boundary conditions used in this study include the inlet velocity in the entrance of cyclone and output pressure in both the upper and lower output sections. Results and Discussion In the results section, the results are initially validated by experimental results. Then, the parameters relating to separation efficiency and pressure drop are discussed. Finally, the tangential and axial velocities are considered as important parameters in the cyclone performance. One of the important issues in the cyclones is the static pressure because it completely affects the phenomenon of separation in the cyclone. The velocities of 16 m s -1 and 18 m s -1 have a good potential for use as the base velocity of the inlet fluid to the cyclone. The velocity of 20 m s -1 is not suitable for separation due to high-pressure drop related to high static pressure. The separation efficiency in the cyclone was 92 to 99% at all levels, the highest separation efficiency of 99% occurred at the velocity of 16 m s -1 and the lowest separation efficiency of 9% happened at the velocity of 20 m s -1 . An increasing trend in axial and radial velocities occurred and the highest tangential velocity occurring in the input section. Considering the working conditions, the inlet velocities of 10 m s -1 to 16 m s -1 are appropriate for the turbulence intensity viewpoint. Conclusion (1): The speeds 16 m s -1 and 18 m s -1 showed a good potential for use as a base velocity of the fluid to the cyclone. (2): The highest separation efficiency for the velocity of 16 m s -1 (99%) and lower isolation efficiency was obtained at velocity of 20 m s -1 (92%). (3): The velocities of 10 m s -1 to 16 m s -1 are suitable input rates from the point of view of turbulence intensity. (4): It is concluded that from the point of view of wear to the velocity of 10 to 16 m s -1 , practical use is possible, and the velocity of 18 m s -1 and 20 m s -1 require the reinforcement of the relevant sections.

There are 80 million light trucks on the road today with suboptimal aerodynamic forms. Previous research has found that several miles per gallon can be saved by specifically tailoring truck bodies for reduced aerodynamic drag. Even greater savings can be obtained if the shape of the trucks is numerically optimized. This could reduce fuel consumption in the United States by billions of gallons per year. The purpose of this research is to develop and quantify optimal light truck canopy designs using computational fluid dynamics (CFD). Both two-dimensional and three-dimensional models are used to do this. Initially, this research focuses on quantifying and generalizing the effects of traditional automotive aerodynamic accessories, such as canopies and air dams. Once the effects of various form factors are quantified an optimization of the canopy is performed. This thesis demonstrates a method for drag reduction using CFD and traditional numerical optimization techniques. Lastly, the optimized forms are physically constructed and their effects on fuel economy are compared to the CFD prediction. The results indicate that the CFD formulation provides an accurate predictor for improving fuel economy and drag characteristics. The prototype air dam and optimally shaped canopy generated a 21.23% savings in terms of fuel economy.

A method for inverse design of horizontal axis wind turbines (HAWTs) is presented in this paper. The direct solver for aerodynamic analysis solves the Reynolds Averaged Navier Stokes (RANS) equations, where the effect of the turbine rotor is modeled as momentum sources using the actuator disk model (ADM); this approach is referred to as RANS/ADM. The inverse problem is posed as follows: for a given selection of airfoils, the objective is to find the blade geometry (described as blade twist and chord distributions) which realizes the desired turbine aerodynamic performance at the design point; the desired performance is prescribed as angle of attack ($\alpha$) and axial induction factor ($a$) distributions along the blade. An iterative approach is used. An initial estimate of blade geometry is used with the direct solver (RANS/ADM) to obtain $\alpha$ and $a$. The differences between the calculated and desired values of $\alpha$ and $a$ are computed and a new estimate for the blade geometry (chord and twist) is obtained via nonlinear least squares regression using the Trust-Region-Reflective (TRF) method. This procedure is continued until the difference between the calculated and the desired values is within acceptable tolerance. The method is demonstrated for conventional, single-rotor HAWTs and then extended to multi-rotor, specifically dual-rotor wind turbines. The TRF method is also compared with the multi-dimensional Newton iteration method and found to provide better convergence when constraints are imposed in blade design, although faster convergence is obtained with the Newton method for unconstrained optimization.

This article is from Patient Safety in Surgery , volume 8 . Abstract Background: Air-borne bacteria in the operating room (OR) may contaminate the surgical wound, either by direct sedimentation from the air or indirectly, by contaminated sterile instruments. Reduced air contamination can be achieved with an efficient ventilation system. The current study assesses the additive effect of a mobile laminar airflow (MLAF) unit on the microbiological air quality in an OR supplied with turbulent-mixing air ventilation. Methods: A recently designed OR in NKS (Nya Karolinska Sjukhuset, Stockholm, Sweden) was the physical model for this study. Simulation was made with MLAF units adjacent to the operating table and the instrument tables, in addition to conventional turbulent-mixing ventilation. The evaluation used numerical calculation by computational fluid dynamics (CFD). Sedimentation rates (CFU/m2/h) were calculated above the operating table and two instrument tables, and in the periphery of the OR. Bacterial air contamination (CFU/m3) was simulated above the surgical and instrument tables with and without the MLAF unit. Results: The counts of airborne and sedimenting, bacteria-carrying particles downstream of the surgical team were reduced to an acceptable level for orthopedic/implant surgery when the MLAF units were added to conventional OR ventilation. No significant differences in mean sedimentation rates were found in the periphery of the OR. Conclusions: The MLAF screen unit can be a suitable option when the main OR ventilation system is unable to reduce the level of microbial contamination to an acceptable level for orthopedic implant surgery. However, MLAF effect is limited to an area within 1 m from the screen. Increasing air velocity from the MLAF above 0.4 m/s does not increase the impact area.

This article is from Journal of Cardiovascular Magnetic Resonance , volume 16 . Abstract None

A computational study was conducted to better understand experimental results obtained from wind tunnel tests of a Mach 4 waverider model and a comparative reference configuration. The experimental results showed that the performance of the reference configuration was slightly better than that of the waverider model. These results contradict waverider design theory, which suggests that a waverider optimized for maximum lift-to-drag should provide better performance than any other non-waverider configuration at a given design point, especially at hypersonic speeds. The computational results showed that the predicted surface pressure values and the integrated lift and drag coefficients from the pressure distributions were much lower for the reference model than for the flat-top model, due to the reference model bottom surface having a slight expansion. The lift-to-drag ratios for the flat-top model were higher due to a relatively low drag for the same amount of lift. These results indicate that the performance advantage of the reference model was due to the shape of the bottom surface and not due to the flat top surface. The results also showed that the reference model exhibited the same shock attachment characteristics as the waverider because the planform shapes were identical. CFD predictions show that the planform shape gives the waverider an advantage in performance over conventional hypersonic vehicles and that altering the bottom surface of a waverider does not cause significant performance degradation.

This paper describes an experiment in which a large-scale scientific application development for tightly-coupled parallel machines is adapted to the distributed execution environment of the Information Power Grid (IPG). A brief overview of the IPG and a description of the computational fluid dynamics (CFD) algorithm are given. The Globus metacomputing toolkit is used as the enabling device for the geographically-distributed computation. Modifications related to latency hiding and Load balancing were required for an efficient implementation of the CFD application in the IPG environment. Performance results on a pair of SGI Origin 2000 machines indicate that real scientific applications can be effectively implemented on the IPG; however, a significant amount of continued effort is required to make such an environment useful and accessible to scientists and engineers.

Design and analysis of the inlet for a rocket based combined cycle engine is discussed. Computational fluid dynamics was used in both the design and subsequent analysis. Reynolds averaged Navier-Stokes simulations were performed using both perfect gas and real gas assumptions. An inlet design that operates over the required Mach number range from 0 to 12 was produced. Performance data for cycle analysis was post processed using a stream thrust averaging technique. A detailed performance database for cycle analysis is presented. The effect ot vehicle forebody compression on air capture is also examined.

Research is still needed to fully understand how different techniques of irrigation affect irrigation dynamics. Apical pressure, wall shear stress, turbulence, irrigant flow pattern, and exchange of irrigating solution are all components of irrigation dynamics. The dynamics of irrigation change depending on the type of root canal disinfection technique used. Numerous techniques have been used in the literature to evaluate the dynamics of the irrigant, including apical pressure devices, dye clearance, recovery trap devices, flow rate and computational fluid dynamics (CFD). The CFD model provides thorough information on the dynamics of the irrigant for evaluating the various assessment methods. Therefore, using computational fluid dynamics, the current systematic review compares positive pressure syringe needle irrigation with other techniques of irrigation to assess the irrigation dynamics.

Validation is the assessment of the accuracy of computational simulations by comparison with experimental data. A well validated computational fluid dynamics model can be of high importance when assessing the safety of medical devices. However, its validation and verification must be conducted before the results can be considered credible. The U.S. Food and Drug Administration has completed a computational inter-laboratory study that showed relatively negative current state of numerical methods used for simulating fluid flow in an idealized medical device, even by self-ascribed experts. Yet, the same numerical methods are commonly used to simulate fluid flow in much more complex geometries, especially when patient-specific geometries need to be used. The study presented here recreated these results with larger number of participants and confirmed the need for proper validation of the numerical methods used. Moreover, the results were analyzed with respect to the use of grid refinement study by the participants.

This article is from Journal of Insect Science , volume 10 . Abstract Polybia spinifex Richards (Hymenoptera: Vespidae) constructs mud nests characterized by a long slit-like entrance. The ventilation and thermal characteristics of the P. spinifex nest were investigated to determine whether the nest microclimate is automatically maintained due to the size of the entrance. In order to examine this hypothesis, a numerical simulation was employed to predict the effects of the entrance length. The calculations were performed with 3D-virtual models that simulated the P. spinifex nest conditions, and the reliability of the simulations was experimentally examined by using gypsum-model nests and a P. spinifex nest. The ventilation effect was determined by blowing air through the nest at 1–3 m/s (airflow conditions); the airspeed was found to be higher in models with a longer entrance. The ventilation rate was also higher in models with longer entrances, suggesting that the P. spinifex nest is automatically ventilated by natural winds. Next, the thermal effect was calculated under condition of direct sunlight. Under a calm condition (airflow, 0 m/s), thermal convection and a small temperature drop were observed in the case of models with a long entrance, whereas the ventilation and thermoregulation effects seemed small. Under airflow conditions, the temperature at the mid combs steeply dropped due to the convective airflow through the entrance at 1–2 m/s, and at 3 m/s, most of the heat was eliminated due to high thermal conductivity of the mud envelope, rather than convection.

Nozzle boattail drag is significant for the High Speed Civil Transport (HSCT) and can be as high as 25 percent of the overall propulsion system thrust at transonic conditions. Thus, nozzle boattail drag has the potential to create a thrust drag pinch and can reduce HSCT aircraft aerodynamic efficiencies at transonic operating conditions. In order to accurately predict HSCT performance, it is imperative that nozzle boattail drag be accurately predicted. Previous methods to predict HSCT nozzle boattail drag were suspect in the transonic regime. In addition, previous prediction methods were unable to account for complex nozzle geometry and were not flexible enough for engine cycle trade studies. A computational fluid dynamics (CFD) effort was conducted by NASA and McDonnell Douglas to evaluate the magnitude and characteristics of HSCT nozzle boattail drag at transonic conditions. A team of engineers used various CFD codes and provided consistent, accurate boattail drag coefficient predictions for a family of HSCT nozzle configurations. The CFD results were incorporated into a nozzle drag database that encompassed the entire HSCT flight regime and provided the basis for an accurate and flexible prediction methodology.

This paper explores use of computational fluid dynamics to study the e?ect of geometric porosity on static stability and drag for NASA's Multi-Purpose Crew Vehicle main parachute. Both of these aerodynamic characteristics are of interest to in parachute design, and computational methods promise designers the ability to perform detailed parametric studies and other design iterations with a level of control previously unobtainable using ground or flight testing. The approach presented here uses a canopy structural analysis code to define the inflated parachute shapes on which structured computational grids are generated. These grids are used by the computational fluid dynamics code OVERFLOW and are modeled as rigid, impermeable bodies for this analysis. Comparisons to Apollo drop test data is shown as preliminary validation of the technique. Results include several parametric sweeps through design variables in order to better understand the trade between static stability and drag. Finally, designs that maximize static stability with a minimal loss in drag are suggested for further study in subscale ground and flight testing.

This viewgraph presentation reviews computational fluid dynamics as a tool for modelling the dispersion of carbon monoxide at the Stennis Space Center's A3 Test Stand. The contents include: 1) Constellation Program; 2) Constellation Launch Vehicles; 3) J2X Engine; 4) A-3 Test Stand; 5) Chemical Steam Generators; 6) Emission Estimates; 7) Located in Existing Test Complex; 8) Computational Fluid Dynamics; 9) Computational Tools; 10) CO Modeling; 11) CO Model results; and 12) Next steps.

An anti-vortex baffle is a liquid propellant management device placed adjacent to an outlet of the propellant tank. Its purpose is to substantially reduce or eliminate the formation of free surface dip and vortex, as well as prevent vapor ingestion into the outlet, as the liquid drains out through the flight. To design an effective anti-vortex baffle, Computational Fluid Dynamic (CFD) simulations were undertaken for the NASA Ares I vehicle LOX tank subjected to the simulated flight loads with and without the anti-vortex baffle. The Six Degree-Of-Freedom (6- DOF) dynamics experienced by the Crew Launch Vehicle (CLV) during ascent were modeled by modifying the momentum equations in a CFD code to accommodate the extra body forces from the maneuvering in a non-inertial frame. The present analysis found that due to large moments, the CLV maneuvering has significant impact on the vortical flow generation inside the tank. Roll maneuvering and side loading due to pitch and yaw are shown to induce swirling flow. The vortical flow due to roll is symmetrical with respect to the tank centerline, while those induced by pitch and yaw maneuverings showed two vortices side by side. The study found that without the anti-vortex baffle, the swirling flow caused surface dip during the late stage of drainage and hence early vapor ingestion. The flow can also be non-uniform in the drainage pipe as the secondary swirling flow velocity component can be as high as 10% of the draining velocity. An analysis of the vortex dynamics shows that the swirling flow in the drainage pipe during the Upper Stage burn is mainly the result of residual vortices inside the tank due to conservation of angular momentum. The study demonstrated that the swirling flow in the drainage pipe can be effectively suppressed by employing the anti-vortex baffle.

Presentation provides an overview of the process to generate aerothermal databases for the Orion MPCV usingcomputational fluid dynamics (CFD) tools.

Experimental techniques to measure rotorcraft aerodynamic performance are widely used. However, most of them are either unable to capture interference effects from bodies, or require an extremely large computational budget. The objective of the present research is to develop an XV-15 Tiltrotor Research Aircraft rotor model for investigation of wind tunnel wall interference using a novel Computational Fluid Dynamics (CFD) solver for rotorcraft, RotCFD. In RotCFD, a mid-fidelity Unsteady Reynolds Averaged Navier-Stokes (URANS) solver is used with an incompressible flow model and a realizable k-ε turbulence model. The rotor is, however, not modeled using a computationally expensive, unsteady viscous body-fitted grid, but is instead modeled using a blade-element model (BEM) with a momentum source approach. Various flight modes of the XV-15 isolated rotor, including hover, tilt, and airplane mode, have been simulated and correlated to existing experimental and theoretical data. The rotor model is subsequently used for wind tunnel wall interference simulations in the National Full-Scale Aerodynamics Complex (NFAC) at Ames Research Center in California. The results from the validation of the isolated rotor performance showed good correlation with experimental and theoretical data. The results were on par with known theoretical analyses. In RotCFD the setup, grid generation, and running of cases is faster than many CFD codes, which makes it a useful engineering tool. Performance predictions need not be as accurate as high-fidelity CFD codes, as long as wall effects can be properly simulated. For both test sections of the NFAC wall, interference was examined by simulating the XV-15 rotor in the test section of the wind tunnel and with an identical grid but extended boundaries in free field. Both cases were also examined with an isolated rotor or with the rotor mounted on the modeled geometry of the Tiltrotor Test Rig (TTR). A \"quasi linear trim\" was used to trim the thrust for the rotor to compare the power as a unique variable. Power differences between free field and wind tunnel cases were found from -7 to 0 percent in the 80- by 120-Foot Wind Tunnel and -1.6 to 4.8 percent in the 40- by 80-Foot Wind Tunnel, depending on the TTR orientation, tunnel velocity, and blade setting. The TTR will be used in 2016 to test the Bell 609 rotor in a similar fashion to the research in this report.

An efficient aerodynamic shape optimization method based on a computational fluid dynamics/sensitivity analysis algorithm has been developed which determines automatically the geometrical definition of an optimal surface starting from any initial arbitrary geometry. This method is not limited to any number of design variables or to any class of surfaces for shape definition.

An efficient aerodynamic shape optimization method based on a computational fluid dynamics/sensitivity analysis algorithm has been developed which determines automatically the geometrical definition of an optimal surface starting from any initial arbitrary geometry. This method is not limited to any number of design variables or to any class of surfaces for shape definition.

Launch vehicles frequently experience a reduced stability margin through the transonic Mach number range. This reduced stability margin can be caused by the aerodynamic undamping one of the lower-frequency flexible or rigid body modes. Analysis of the behavior of a flexible vehicle is routinely performed with quasi-steady aerodynamic line loads derived from steady rigid aerodynamics. However, a quasi-steady aeroelastic stability analysis can be unconservative at the critical Mach numbers, where experiment or unsteady computational aeroelastic analysis show a reduced or even negative aerodynamic damping.Amethod of enhancing the quasi-steady aeroelastic stability analysis of a launch vehicle with unsteady aerodynamics is developed that uses unsteady computational fluid dynamics to compute the response of selected lower-frequency modes. The response is contained in a time history of the vehicle line loads. A proper orthogonal decomposition of the unsteady aerodynamic line-load response is used to reduce the scale of data volume and system identification is used to derive the aerodynamic stiffness, damping, and mass matrices. The results are compared with the damping and frequency computed from unsteady computational aeroelasticity and from a quasi-steady analysis. The results show that incorporating unsteady aerodynamics in this way brings the enhanced quasi-steady aeroelastic stability analysis into close agreement with the unsteady computational aeroelastic results.

Introduction Today, the development of the livestock industry and feed supply is a vital issue due to the growing world population, the importance of animal protein supply, and the growing requirement for livestock products. A porous medium refers to a solid-void (pore) space that is occupied by a fluid (gas or liquid). Generally, many of these pores are interconnected which makes the transportation of mass and heat possible through the pores and this contributes to a faster transportation process through the solid matrix. Porosity is the fraction of void space to total volume. While the pores are large enough, water vapor and air in the porous media can be transported by molecular diffusion. Molecular diffusion of a gas species (e.g., vapor) in a gas mixture (e.g., vapor and air) is described by Fick’s law. Materials and Methods In this study, the samples were classified into four categories, including control, 3-impacts (low conditioning), 8-impacts (average conditioning), and 13-impacts (high conditioning). Each category included six samples (50-grams) that were used to measure different characteristics at different stages. All samples were weighed every two hours using a digital scale (0.001 gr precision). The leaf-stem separation force then was extracted using a texture analyzer. All experiments were repeated three times, and finally, the mean of these three repetitions was reported as the final value for the intended parameter. The geometry of the alfalfa stem was drawn in Gambit software and after meshing and applying boundary conditions; it was transferred to ANSYS Fluent software. Then, while the solver was selected, adjusted under relaxation factors were applied. In the following, mesh independency was checked and the results were reported. Results and Discussion To ensure numerical accuracy, the experimental data should be validated with the simulation results. For this purpose, experimental moisture losses were compared to the software results and showed a good agreement. Then, the moisture ratio curves (kinetics of drying) and force-time chart were presented. The impact of the moisture content of the tissue was evaluated on the value of force per time. Therefore, three samples of alfalfa with different relative humidity in terms of leaf-stem separation force were reported. The results of the numerical simulations were presented as two main contours: the velocity magnitude and moisture (water vapor) mass fraction. The simulation results were provided for all different modes and compared to the experimental data. Finally, errors between both results were presented in a table. Conclusion Regarding the quality and losses of the final product and comparisons between four different modes (control, 3 impacts, 8 impacts, and 13 impacts), the mode with 8 impacts was selected as the best mode. The Force-time chart illustrated two peaks due to the special multi-layer texture of the alfalfa. Regarding reducing the moisture ratio of the alfalfa as compared to the optimal, the force required to separate the leaves from the alfalfa stem was significantly decreased. Also, a significant increase in the losses was observed for impacts modes higher than 8.

System identification has long been used as a tool for flight test engineers to characterize systems under test; however, the inputs to these characterization activities have previously been limited to wind tunnel and flight test data. There has been a recent effort to incorporate computational fluid dynamics (CFD) into the system identification process. An integral piece of the process is the simulation of training maneuvers utilizing CFD. Up until now, the suitability of particular training maneuvers has been assessed by comparing the reduced model to known results. This research strives to recommend a set of parameters to be used in determining a priori whether a training maneuver will be suitable under a particular set of flow conditions.

A thorough understanding of dynamic interactions between inlets and compressors is extremely important to the design and development of propulsion control systems, particularly for supersonic aircraft such as the High-Speed Civil Transport (HSCT). Computational fluid dynamics (CFD) codes are routinely used to analyze individual propulsion components. By coupling the appropriate CFD component codes, it is possible to investigate inlet-compressor interactions. The objectives of this work were to gain a better understanding of inlet-compressor interaction physics, formulate a more realistic compressor-face boundary condition for time-accurate CFD simulations of inlets, and to take a first step toward the CFD simulation of an entire engine by coupling multidimensional component codes. This work was conducted at the NASA Lewis Research Center by a team of civil servants and support service contractors as part of the High Performance Computing and Communications Program (HPCCP).

The automotive, chemical and other plants employs use of cooling tower dissipating heat from water in to the atmosphere. The performance of cooling tower can be enhanced by various water modelling and energy consumption analysis. The current research reviews previous studies conducted in determination of effectiveness of cooling tower subjected to different operating conditions. The analytical equations are presented along with experimental data on evaluation and improvement of cooling tower performance. P Chandra Shekhar | Sudhir Singh Rajput "Thermal Analysis of Cooling Tower using Computational Fluid Dynamics" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-6 | Issue-2 , February 2022, URL: https://www.ijtsrd.com/papers/ijtsrd49160.pdf Paper URL: https://www.ijtsrd.com/engineering/mechanical-engineering/49160/thermal-analysis-of-cooling-tower-using-computational-fluid-dynamics/p-chandra-shekhar

This document in large part is based on the Masters Thesis of Cole Stephens. The document encompasses a variety of technical and practical issues involved when using the STARS codes for Aeroservoelastic analysis of vehicles. The document covers in great detail a number of technical issues and step-by-step details involved in the simulation of a system where aerodynamics, structures and controls are tightly coupled. Comparisons are made to a benchmark experimental program conducted at NASA Langley. One of the significant advantages of the methodology detailed is that as a result of the technique used to accelerate the CFD-based simulation, a systems model is produced which is very useful for developing the control law strategy, and subsequent high-speed simulations.

A thermal convection loop is a annular chamber filled with water, heated on the bottom half and cooled on the top half. With sufficiently large forcing of heat, the direction of fluid flow in the loop oscillates chaotically, dynamics analogous to the Earth's weather. As is the case for state-of-the-art weather models, we only observe the statistics over a small region of state space, making prediction difficult. To overcome this challenge, data assimilation (DA) methods, and specifically ensemble methods, use the computational model itself to estimate the uncertainty of the model to optimally combine these observations into an initial condition for predicting the future state. Here, we build and verify four distinct DA methods, and then, we perform a twin model experiment with the computational fluid dynamics simulation of the loop using the Ensemble Transform Kalman Filter (ETKF) to assimilate observations and predict flow reversals. We show that using adaptively shaped localized covariance outperforms static localized covariance with the ETKF, and allows for the use of less observations in predicting flow reversals. We also show that a Dynamic Mode Decomposition (DMD) of the temperature and velocity fields recovers the low dimensional system underlying reversals, finding specific modes which together are predictive of reversal direction.

The Scale Model Acoustic Test (SMAT) is a 5% scale test of the Space Launch System (SLS), which is currently being designed at Marshall Space Flight Center (MSFC). The purpose of this test is to characterize and understand a variety of acoustic phenomena that occur during the early portions of lift off, one being the overpressure environment that develops shortly after booster ignition. The pressure waves that propagate from the mobile launcher (ML) exhaust hole are defined as the ignition overpressure (IOP), while the portion of the pressure waves that exit the duct or trench are the duct overpressure (DOP). Distinguishing the IOP and DOP in scale model test data has been difficult in past experiences and in early SMAT results, due to the effects of scaling the geometry. The speed of sound of the air and combustion gas constituents is not scaled, and therefore the SMAT pressure waves propagate at approximately the same speed as occurs in full scale. However, the SMAT geometry is twenty times smaller, allowing the pressure waves to move down the exhaust hole, through the trench and duct, and impact the vehicle model much faster than occurs at full scale. The DOP waves impact portions of the vehicle at the same time as the IOP waves, making it difficult to distinguish the different waves and fully understand the data. To better understand the SMAT data, a computational fluid dynamics (CFD) analysis was performed with a fictitious geometry that isolates the IOP and DOP. The upper and lower portions of the domain were segregated to accomplish the isolation in such a way that the flow physics were not significantly altered. The Loci/CHEM CFD software program was used to perform this analysis.

With the recent interest in novel control effectors there is a need to determine the stability and control derivatives of new aircraft configurations early in the design process. These derivatives are central to most control law design methods and would allow the determination of closed-loop control performance of the vehicle. Early determination of the static and dynamic behavior of an aircraft may permit significant improvement in configuration weight, cost, stealth, and performance through multidisciplinary design. The classical method of determining static stability and control derivatives - constructing and testing wind tunnel models - is expensive and requires a long lead time for the resultant data. Wind tunnel tests are also limited to the preselected control effectors of the model. To overcome these shortcomings, computational fluid dynamics (CFD) solvers are augmented via automatic differentiation, to directly calculate the stability and control derivatives. The CFD forces and moments are differentiated with respect to angle of attack, angle of sideslip, and aircraft shape parameters to form these derivatives. A subset of static stability and control derivatives of a tailless aircraft concept have been computed by two differentiated inviscid CFD codes and verified for accuracy with central finite-difference approximations and favorable comparisons to a simulation database.

The Web provides new Methods for accessing Information world-wide, but the current text-and-pictures approach neither utilizes all the Web's possibilities not provides for its limitations. While the inclusion of pictures and animations in a paper communicates more effectively than text alone, It Is essentially an extension of the concept of "publication." Also, as use of the Web increases putting images and animations online will quickly load even the "Information Superhighway." We need to find forms of communication that take advantage of the special nature of the Web. This paper presents one approach: the use of the Internet and the Mosaic interface for data sharing and collaborative analysis. We will describe (and In the presentation, demonstrate) our approach: using FAST (Flow Analysis Software Toolkit), a scientific visualization package, as a data viewer and interactive tool called from MOSAIC. Our intent is to stimulate the development of other tools that utilize the unique nature of electronic communication.

The application of a sweeping jet actuator to a circulation control system was initiated by a risk reduction series of experiments to optimize the authority of a single sweeping jet actuator. The sweeping jet design was integrated into the existing Fundamental Aerodynamic Subsonic Transonic- Modular Active Control (FAST-MAC) model by replacing the steady blowing system with an array of thirty-nine sweeping jet cartridges. A constant slot height to wing chord ratio was similar to the steady blowing configuration resulting in each actuator having a unique in size for the sweeping jet configuration. While this paper will describe the scaling and optimization of the actuators for future high Reynolds number applications, the major focus of this effort was to target the transonic flight regime by increasing the amplitude authority of the actuator. This was accomplished by modifying the diffuser of the sweeping jet actuator, and this paper highlights twelve different diffuser designs. The experimental portion of this work was completed in the NASA Langley National Transonic Facility.

The results of an investigation into the feasibility of using the MPP for direct and large eddy simulations of the Navier-Stokes equations is presented. A major part of this study was devoted to the implementation of two of the standard numerical algorithms for CFD. These implementations were not run on the Massively Parallel Processor (MPP) since the machine delivered to NASA Goddard does not have sufficient capacity. Instead, a detailed implementation plan was designed and from these were derived estimates of the time and space requirements of the algorithms on a suitably configured MPP. In addition, other issues related to the practical implementation of these algorithms on an MPP-like architecture were considered; namely, adaptive grid generation, zonal boundary conditions, the table lookup problem, and the software interface. Performance estimates show that the architectural components of the MPP, the Staging Memory and the Array Unit, appear to be well suited to the numerical algorithms of CFD. This combined with the prospect of building a faster and larger MMP-like machine holds the promise of achieving sustained gigaflop rates that are required for the numerical simulations in CFD.

Computational Fluid Dynamics (CFD) is the standard numerical tool used by Fluid Dynamists to estimate solutions to many problems in academia, government, and industry. CFD is known to have errors and uncertainties and there is no universally adopted method to estimate such quantities. This paper describes an approach to estimate CFD uncertainties strictly numerically using inputs and the Student-T distribution. The approach is compared to an exact analytical solution of fully developed, laminar flow between infinite, stationary plates. It is shown that treating all CFD input parameters as oscillatory uncertainty terms coupled with the Student-T distribution can encompass the exact solution.

Analytical methods and computational fluid dynamics are used to describe flow conditions encountered at Naval Research Laboratory's Ballast Water Treatment Test Facility. Design tradeoffs are examined in the engineering of sample ports for collecting biological organisms in water samples, and criteria are provided for sample port installation in shipboard piping systems. Results of this work show that the ideal geometry for biological sampling is from the centerline of a straight, vertical, upward-flowing pipe having a sample port diameter between 1.5 and 2.0 times the basic isokinetic diameter as defined in this report. Sample ports should use ball valves for isolation purposes, and diaphragm or venturi valves for flow control; they should be located as close to the overboard outlet as possible; and they should be positioned as far from upstream obstructions and fittings as possible.

In the current globalization, we can see many innovations being introduced or implemented in every aspect of field that are considered to be existed. Every country is aiming to develop its power over all the aspects that considered for comparison with other countries in order to stand at same level of competition with others. One such power considered by all countries to develop every possible way to have a healthy competition is the military power which involves basically innovations of fast moving aircraft having a high lift coefficient and low drag coefficient. Such an aircraft having the high lift and low drag coefficient is TEJAS (HAL) developed by country India on which the purpose of paper mainly sustains. The paper mainly focuses on steady-state flow analysis over aircraft TEJAS using the computer aided modelling techniques and also the comparison of the results obtained from the modelled techniques. The paper also outlines the designing of the structural model of the TEJAS in a modelling software, creation of a finite computational domain, segmentation of this domain into discrete intervals, applying boundary conditions such as velocity in order to obtain plots and desired results determining the coefficient of pressure, lift and drag coefficient, velocity magnitude etc. This paper also aims in creating awareness to the future students about the techniques involved and knowledge required for developing a designed modelled. This paper also highlights the use of CFD techniques involved for the purpose of fluid flow simulation of the aircraft especially performing the meshing techniques, pre and post processing techniques and finally the evaluation of the simulation. Finally this paper can be seen as source by future generation students in gaining knowledge about design, analysis and simulation of the structured model on various conditions, about the field of aerospace engineering and new innovations being developed and also about the career involved when the above fields were chosen foe specialization purposes

With the recent development of capabilities for predicting the damping derivatives, it is now possible to predict the stability characteristics and free-flight motion for projectiles using data that are derived solely from computational fluid dynamics (CFD). As a demonstration of the capability, this report presents results for a family of axisymmetric projectiles in supersonic flight. The particular configuration selected for this computational study has been extensively tested in aeroballistic ranges, and high-quality experimental data have been obtained. Thin-layer Navier-Stokes techniques have been applied to compute the attached viscous flow over the forebody of the projectile and the separated flow in the projectile base region. Using the predicted aerodynamics coefficients, parameters that characterize the in-flight motion are subsequently evaluated, including the gyroscopic and dynamic stability factors, and the projectile's fast and slow mode frequencies and damping coefficients. These parameters are then used to predict the free-flight motion of the projectile. In each case, the computational approach is validated by comparison with experimental data, and very good agreement between computation and experiment is found. It is believed that this demonstration represents the first known instance of a viscous CFD approach being applied to predict all the necessary data for performance of linear aerodynamics stability and trajectory analyses.

Computational Fluid Dynamics (CFD) Modeling of Heat Transfer in a Polymeric-Membrane using Finite Volume Method 作者： Ahsan, M. 1 Hussain, A. 1 作者单位： 1. NUST, SCME, Islamabad, Pakistan. 提交时间： 2017-11-02 摘要: The efficiency, robustness and reliability of recent numerical methods for finding solutions to flow problems have given rise to the implementation of computational fluid dynamics (CFD) as a broadly used analysis method for engineering problems like membrane separation system. The CFD modeling in this study observes steady and unsteady (transient) heat flux and temperature profiles in a polymeric (cellulose acetate) membrane. This study is novel due to the implementation of user defined scalar (LIDS) diffusion equation by using user-defined functions (UDFs) infinite volume method (FVM). Some details of the FVM used by the solver are carefully discussed when implementing terms in the governing equation and boundary conditions (BC). The contours of temperature due to high-temperature gradient are reported for steady and unsteady problems. Computational fluid dynamics finite volume method heat transfer cellulose acetate based membrane numerical-simulation turbulence promoters narrow channel 分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 引用： ChinaXiv:201711.00015 (或此版本 ChinaXiv:201711.00015V1 ) doi:10.12074/201711.00015 CSTR:32003.36.ChinaXiv.201711.00015.V1 推荐引用方式： Ahsan, M.,Hussain, A..(2017).Computational Fluid Dynamics (CFD) Modeling of Heat Transfer in a Polymeric-Membrane using Finite Volume Method.热科学学报.[ChinaXiv:201711.00015] 版本历史 [V1] 2017-11-02 14:52:11 ChinaXiv:201711.00015V1 下载全文

The propagation characteristics of several helicopter airfoil profiles have been investigated using the transonic small disturbance equation. A test case was performed to generate a moving shock that propagated off the airfoil. Various grids were then examined to determine their ability to accurately capture these propagating shock waves. Finally, the case of airfoil vortex interactions was thoroughly studied over a wide range of Mach numbers and airfoil shapes with particular emphasis on the transonic regime; this results in a highly complicated fluctuation of lift, drag, and pitching moment. The calculated acoustic intensity levels, along with the details of the computational flow field, provide new insights into the understanding of transonic airfoil vortex interactions.

Early experimental work, conducted at Defence R and D Canada Suffield, measured and characterized the personal and environmental contamination associated with simulated anthrax-tainted letters under a number of different scenarios in order to obtain a better understanding of the physical and biological processes for detecting, assessing, and formulating potential mitigation strategies for managing the risks associated with opening an anthrax-tainted letter. These preliminary experimental investigations have been extended in the present study to simulate the contamination from anthrax-tainted letters in an Open-Office environment using Computational Fluid Dynamics (CFD). A quantity of 0.1 g of a biological simulant Bacillus globigii (BG) for anthrax was released from an opened letter in the experiment. The accuracy of the model for prediction of the spatial distribution of BG spores in the office from the opened letter is assessed qualitatively (and to the extent possible, quantitatively) by detailed comparison with measured BG concentrations obtained under a number of scenarios, some involving people moving within the office. It is hypothesized that the discrepancy between the numerical predictions and experimental measurements of concentration were mainly caused by :(1) air flow leakage from cracks and crevices in the walls and windows of the building shell; (2) decoupling between the present CFD simulation and dispersion of BG spores in the Heating, Ventilation, and Air Conditioning (HVAC) system; (3) the effect of deposition and re-suspension of BG spores not being considered in the present CFD simulations. Although there is still a scope of further improvement in the present CFD simulation, it should be emphasized here that the advantages of utilization of CFD modeling for assessment and design of mitigation strategies and protocols for defence against anthrax-tainted letters over an experimentally based approach to the problem are obvious:

There are 80 million light trucks on the road today with suboptimal aerodynamic forms. Previous research has found that several miles per gallon can be saved by specifically tailoring truck bodies for reduced aerodynamic drag. Even greater savings can be obtained if the shape of the trucks is numerically optimized. This could reduce fuel consumption in the United States by billions of gallons per year. The purpose of this research is to develop and quantify optimal light truck canopy designs using computational fluid dynamics (CFD). Both two-dimensional and three-dimensional models are used to do this. Initially, this research focuses on quantifying and generalizing the effects of traditional automotive aerodynamic accessories, such as canopies and air dams. Once the effects of various form factors are quantified an optimization of the canopy is performed. This thesis demonstrates a method for drag reduction using CFD and traditional numerical optimization techniques. Lastly, the optimized forms are physically constructed and their effects on fuel economy are compared to the CFD prediction. The results indicate that the CFD formulation provides an accurate predictor for improving fuel economy and drag characteristics. The prototype air dam and optimally shaped canopy generated a 21.23% savings in terms of fuel economy.

The design and analysis of recoil systems for direct fire weapons has been conducted at Benet for the last 25 years. The model developed employs the Bernoulli Equation to establish the relationship between flow rate and back pressure within the internal paths and through the primary orifice of the recoil brake. This displacement varying orifice provides the throttling mechanism needed to generate back pressure which opposes the ballistic driving load and arrests the gun in recoil. An orifice is designed to maintain constant upstream pressure over the complete length of recoil, thus minimizing the load transferred to the gun support and vehicle. The equation which models this type of orifice requires an discharge coefficient (Cd) which 'lumps' all of the flow losses due to contraction and directional change of the fluid stream. This coefficient is constant regardless of fluid properties, flow regimes and geometries. Test data from firing tests and research experiments indicate that this may not be the case. This report presents the details of using an offline CFD analysis to establish the flow response characteristics of a typical recoil brake orifice and a methodology of incorporating these results via a lookup table of Cd values into the lumped parameter recoil analysis model developed at Benet Labs.

No abstract available

ABSTRACT A gas turbine can combustor is designed to burn the fuel efficiently while reducing the NOx and CO emissions, and lowering the wall temperature. Environmental challenges with gas turbine include low levels of NOx, CO and soot amongst other pollutants. There is a need for new concepts and technology to satisfy the pollutants emission regulations and to enhance energy conservation. Specifically, ultra-low NOx combustor technology is required to meet the ozone depletion challenge. Researchers now face a challenge of developing dry low-NOx emitting stationary and aero engines. However, any concept for environmental pollution control requires a detailed understanding of the physical and the chemical processes that occur during combustion. In this paper, a three dimensional numerical investigation of the Combustion methane air mixture in a gas turbine can combustor is carried out by using ANSYS. The objective of the study is to understand the combustion phenomena at different planes. The various parameters like air-fuel ratio, velocity of primary air inlet are used to investigate the effects on parameters like combustion chamber on different plane performance and emission. A premixing tube is augmented with the combustion chamber which has a primary air inlet port and three gaseous fuel inlet ports. Air–methane mixture is considered to enter the combustion zone with inlet swirl. The homogeneity of mixture before and after swirl and other important conditions are calculated from simulation and are reported with the help ANSYS FLUENT. Weighted averages of velocity magnitude distribution and mass fractions of methane have been studied at different planes.

A method to efficiently generate a complete aerodynamic description for projectile flight dynamic modeling is described. At the core of the method is an unsteady, time-accurate computational fluid dynamics simulation that is tightly coupled to a rigid projectile flight dynamic simulation. A set of short time snippets of simulated projectile motion at different Mach numbers is computed and employed as baseline data. For each time snippet, aerodynamic forces and moments and the full rigid body state vector of the projectile are known. With time-synchronized air loads and state vector information, aerodynamic coefficients can be estimated with a simple fitting procedure. By inspecting the condition number of the fitting matrix, we can assess the suitability of the time history data to predict a selected set of aerodynamic coefficients. The technique is exercised on an exemplar fin-stabilized projectile with good results.

Nozzle boattail drag is significant for the High Speed Civil Transport (HSCT) and can be as high as 25% of the overall propulsion system thrust at transonic conditions. Thus, nozzle boattail drag has the potential to create a thrust-drag pinch and can reduce HSCT aircraft aerodynamic efficiencies at transonic operating conditions. In order to accurately predict HSCT performance, it is imperative that nozzle boattail drag be accurately predicted. Previous methods to predict HSCT nozzle boattail drag were suspect in the transonic regime. In addition, previous prediction methods were unable to account for complex nozzle geometry and were not flexible enough for engine cycle trade studies. A computational fluid dynamics (CFD) effort was conducted by NASA and McDonnell Douglas to evaluate the magnitude and characteristics of HSCT nozzle boattail drag at transonic conditions. A team of engineers used various CFD codes and provided consistent, accurate boattail drag coefficient predictions for a family of HSCT nozzle configurations. The CFD results were incorporated into a nozzle drag database that encompassed the entire HSCT flight regime and provided the basis for an accurate and flexible prediction methodology.

The process of remote laser welding is simulated in this study to identify the keyhole-induced porosity generation mechanisms and keyhole. Three processes are simulated and discussed: laser power levels, laser-beam shaping configurations, and laser keyhole process. The simulation finding reveals that pore development is caused by strong melt flow behind the keyhole. As verification, the equivalent experimental test is also carried out. According to the findings, a welding speed with a high level helps to keep the keyholes released and prevents the flow of strong melt; a big advanced leaning-angle also provides inactive molten pool flow, making it difficult for bubbles to float to the backside of the molten pool. The conclusions of this study offer crucial insight into the method of porosity of aluminum (Al) alloys laser welding, as well as advice on how to avoid keyhole-induced porosity. It is also obtained that a smaller laser beam with constant power raises the velocity, welding pool depth, and liquid metal temperature.

Introduction Large industrial factories often discharge significant quantities of low-pressure steam (dead steam) into the atmosphere, which causes energy losses. Retaining low-pressure steam content reduces boiler load, resulting in energy savings and lower costs for the fuel consumption (for example, gas consumption bill in a factory). The boosted-pressure steam is used in processes such as distillation, hot water production, space heating or vacuum generation. If the vapor pressure for the intended application is low, a thermo-compressor is able to increase the pressure and temperature to the required level. Thermo-compressors are a special type of gas compressor that uses an actuator to compress secondary fluid and does not have any blades or moving parts. The accurate prediction of the thermo-compressor performance improves the reliability of this process and increases its efficiency. Materials and Methods Two important characteristics for the current thermo-compressors are entrainment ratio (ER) and compression ratio (CR). The first is the dimensionless mass flow rate, and the second is the dimensionless pressure. The wet steam theory as a classic theory is used by Wolmer-Frankel-Zeldovich to calculate the amount of liquid particles. In order to select the best geometry for the thermo-compressor among all possible geometries, the performance of each model must be compared with other models. In following, the case that includes characteristic parameters associated with the target values has been selected. The commercial Ansys Fluent Versions 15, based on the finite volume method (FVM) was used to simulate and monitoring the flow behavior inside the thermo-compressor. The governing partial differential equations (PDE) were solved implicitly using a density-based solution. The convective heat transfer terms were discriminated based on the second-order upwind scheme. The non-linear governing equations were solved using the implicit coupling solver and the standard wall function was used near the wall. Given the three-dimensional flow for steam, the equations of mass conservation, momentum, and energy were written. The Realizable  model was used to simulate turbulences in the flow. Results and Discussion A summary of the results is presented in terms of the results of pressure, velocity magnitude, Mach number and temperature. A general understanding of this characteristic for a thermo-compressor is extremely important for recognizing the fluid flow inside it, and it is very useful for practical use. Pressure is the most important factor in the recharge section of a thermo-compressor. Increasing the recharge vapor pressure in a thermos-compressor revival the dead steam and increases the steam efficiency. The revival steam can be used in other parts because of their high thermal content. Another important factor in the study of flow behavior inside the thermocouple is velocity magnitude. This quantity, which is closely related to the concept of momentum inside the thermocouple, had high influences from high pressure inputs as well as the thermo-compressor geometry. The highest amount of velocity occurs after the initial nozzle and had a very high magnitude (1000 ms -1 ), which was also remarkably high in Monnet's terms. Another important characteristic of a flow is the temperature of the stream. The high input temperature associated with motive vapor at the outlet of the primary nozzle was sharply reduced, even in some section reached to 110 °Kelvin. Due to the very high flow momentum in this section, the fluid phase remained gas and it can be justified from the point of view of the fluid dynamics. Conclusion Considering the importance of thermodynamic properties of steam in conversion and industries, it would be extremely beneficial to fully understand the interactions inside the thermocouple compressor. The importance of the discussed characteristics is more specific when there is a close relationship between each of these factors and energy consumption in a factory or in any industrial production unit. It was observed that the designed thermos-compressor was able to increase the velocity and temperature in a desirable range for the conversion of non-consumable vapor to the pressure and temperature. It was concluded that the Realizable  model due to the prediction of the jet characteristics appearing in the flow regimes for axial symmetry had a high ability to simulate fluid flows inside the thermos-compressor.

No abstract available