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

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

This article is from BioMedical Engineering OnLine , volume 13 . Abstract Background: Left pulmonary artery sling (LPAS) is a rare but severe congenital anomaly, in which the stenoses are formed in the trachea and/or main bronchi. Multi-detector computed tomography (MDCT) provides useful anatomical images, but does not offer functional information. The objective of the present study is to quantitatively analyze the airflow in the trachea and main bronchi of LPAS subjects through computational fluid dynamics (CFD) simulation. Methods: Five subjects (four LPAS patients, one normal control) aging 6-19 months are analyzed. The geometric model of the trachea and the two main bronchi is extracted from the MDCT images. The inlet velocity is determined based on the body weight and the inlet area. Both the geometric model and personalized inflow conditions are imported into CFD software, ANSYS. The pressure drop, mass flow ratio through two bronchi, wall pressure, flow velocity and wall shear stress (WSS) are obtained, and compared to the normal control. Results: Due to the tracheal and/or bronchial stenosis, the pressure drop for the LPAS patients ranges 78.9 - 914.5 Pa, much higher than for the normal control (0.7 Pa). The mass flow ratio through the two bronchi does not correlate with the sectional area ratio if the anomalous left pulmonary artery compresses the trachea or bronchi. It is suggested that the C-shaped trachea plays an important role on facilitating the air flow into the left bronchus with the inertia force. For LPAS subjects, the distributions of velocities, wall pressure and WSS are less regular than for the normal control. At the stenotic site, high velocity, low wall pressure and high WSS are observed. Conclusions: Using geometric models extracted from CT images and the patient-specified inlet boundary conditions, CFD simulation can provide vital quantitative flow information for LPAS. Due to the stenosis, high pressure drops, inconsistent distributions of velocities, wall pressure and WSS are observed. The C-shaped trachea may facilitate a larger flow of air into the left bronchus under the inertial force, and decrease the ventilation of the right lung. Quantitative and personalized information may help understand the mechanism of LPAS and the correlations between stenosis and dyspnea, and facilitate the structural and functional assessment of LPAS.

We introduce a modified and simplified version of the pre-existing fully parallelized three-dimensional Navier--Stokes flow solver known as TPLS. We demonstrate how the simplified version can be used as a pedagogical tool for the study of computational fluid dynamics and parallel computing. TPLS is at its heart a two-phase flow solver, and uses calls to a range of external libraries to accelerate its performance. However, in the present context we narrow the focus of the study to basic hydrodynamics and parallel computing techniques, and the code is therefore simplified and modified to simulate pressure-driven single-phase flow in a channel, using only relatively simple Fortran 90 code with MPI parallelization, but no calls to any other external libraries. The modified code is analysed in order to both validate its accuracy and investigate its scalability up to 1000 CPU cores. Simulations are performed for several benchmark cases in pressure-driven channel flow, including a turbulent simulation, wherein the turbulence is incorporated via the large-eddy simulation technique. The work may be of use to advanced undergraduate and graduate students as an introductory study in computational fluid dynamics, while also providing insight for those interested in more general aspects of high-performance computing.

Spurious stable as well as unstable steady state numerical solutions, spurious asymptotic numerical solutions of higher period, and even stable chaotic behavior can occur when finite difference methods are used to solve nonlinear differential equations (DE) numerically. The occurrence of spurious asymptotes is independent of whether the DE possesses a unique steady state or has additional periodic solutions and/or exhibits chaotic phenomena. The form of the nonlinear DEs and the type of numerical schemes are the determining factor. In addition, the occurrence of spurious steady states is not restricted to the time steps that are beyond the linearized stability limit of the scheme. In many instances, it can occur below the linearized stability limit. Therefore, it is essential for practitioners in computational sciences to be knowledgeable about the dynamical behavior of finite difference methods for nonlinear scalar DEs before the actual application of these methods to practical computations. It is also important to change the traditional way of thinking and practices when dealing with genuinely nonlinear problems. In the past, spurious asymptotes were observed in numerical computations but tended to be ignored because they all were assumed to lie beyond the linearized stability limits of the time step parameter delta t. As can be seen from the study, bifurcations to and from spurious asymptotic solutions and transitions to computational instability not only are highly scheme dependent and problem dependent, but also initial data and boundary condition dependent, and not limited to time steps that are beyond the linearized stability limit.

The Shaped Sonic Boom Demonstration project showed for the first time that by careful design of aircraft contour the resultant sonic boom can maintain a tailored shape, propagating through a real atmosphere down to ground level. In order to assess the propagation characteristics of the shaped sonic boom and to validate computational fluid dynamics codes, airborne measurements were taken of the pressure signatures in the near field by probing with an instrumented F-15B aircraft, and in the far field by overflying an instrumented L-23 sailplane. This paper describes each aircraft and their instrumentation systems, the airdata calibration, analysis of the near- and far-field airborne data, and shows the good to excellent agreement between computational fluid dynamics solutions and flight data. The flights of the Shaped Sonic Boom Demonstration aircraft occurred in two phases. Instrumentation problems were encountered during the first phase, and corrections and improvements were made to the instrumentation system for the second phase, which are documented in the paper. Piloting technique and observations are also given. These airborne measurements of the Shaped Sonic Boom Demonstration aircraft are a unique and important database that will be used to validate design tools for a new generation of quiet supersonic aircraft.

NAS 1.55:10038-Vol-1 Digitized from IA1177307-08-0015 , IA1177307-08-0016 , IA1177307-08-0017 , IA1177307-08-0018 , IA1177307-08-0019 .

This article is from Journal of Human Kinetics , volume 29 . Abstract Nowadays the underwater gliding after the starts and the turns plays a major role in the overall swimming performance. Hence, minimizing hydrodynamic drag during the underwater phases should be a main aim during swimming. Indeed, there are several postures that swimmers can assume during the underwater gliding, although experimental results were not conclusive concerning the best body position to accomplish this aim. Therefore, the purpose of this study was to analyse the effect in hydrodynamic drag forces of using different body positions during gliding through computational fluid dynamics (CFD) methodology. For this purpose, two-dimensional models of the human body in steady flow conditions were studied. Two-dimensional virtual models had been created: (i) a prone position with the arms extended at the front of the body; (ii) a prone position with the arms placed alongside the trunk; (iii) a lateral position with the arms extended at the front and; (iv) a dorsal position with the arms extended at the front. The drag forces were computed between speeds of 1.6 m/s and 2 m/s in a two-dimensional Fluent® analysis. The positions with the arms extended at the front presented lower drag values than the position with the arms aside the trunk. The lateral position was the one in which the drag was lower and seems to be the one that should be adopted during the gliding after starts and turns.

The focus of research in the computational fluid dynamics (CFD) area is two fold: (1) to develop new approaches for turbulence modeling so that high speed compressible flows can be studied for applications to entry and re-entry flows; and (2) to perform research to improve CFD algorithm accuracy and efficiency for high speed flows. Research activities, faculty and student participation, publications, and financial information are outlined.

The focus of research in the computational fluid dynamics (CFD) area is two fold: (1) to develop new approaches for turbulence modeling so that high speed compressible flows can be studied for applications to entry and re-entry flows; and (2) to perform research to improve CFD algorithm accuracy and efficiency for high speed flows. Research activities, faculty and student participation, publications, and financial information are outlined.

This report presents an overview of the software developed under the common high performance computing software support initiative (CHSSI), computational fluid dynamics (CFD)-6 project. Under the project, a zonal Navier-Stokes flow solver tested and validated via years of productive research at the U.S. Army Research Laboratory was rewritten for scalable parallel performance on both shared memory and distributed memory high performance computers. At the same time, a graphical user interface (GUI) was developed to help the user set up the problem, provide real-time visualization, and execute the solver. The GUI is not just an input interface but provides an environment for the systematic, coherent execution of the solver, thus making it a more useful, quicker and easier application tool for engineers. Also part of the CHSSI project is a demonstration of the developed software on complex applications of interest to the Department of Defense (DoD). Results from computations of 10 brilliant antitank (BAT) submunitions simultaneously ejecting from a single Army tactical missile and a guided multiple launch rocket system missile are discussed. Experimental data were available for comparison with the BAT computations. The CFD computations and the experimental data show good agreement and serve as validation for the accuracy of the solver. The software has been written with large memory requirements and scalability in mind. For a grid size of 59 million points, the performance achieved on an Silicon Graphics, Incorporated, Origin 2000 with 96 processors is 18 times the performance that could be achieved via a computer with the processing speed of a single Cray C-90 Processor.

The powering requirement of a ship is one of the most important aspects of naval architecture. Traditionally, ships have been tested for hull resistance using hydrodynamic tank testing. Tank testing evaluates models of ships by measuring their resistance in a tow tank. This has proved to be useful and accurate, but is very time consuming, expensive, and has inherent scaling errors. Because of these reasons, today many vessels are sold on the market without any model testing. Another set of design tools is parametric predictions. Parametric predictions contain acquired data for a specific family of hull forms and use key hull parameters to evaluate a particular design. Parametric predictions run quickly, but cannot be used to evaluate any hull outside of the limits of previously tested hulls. Computational Fluid Dynamics (CFD) codes are a much newer method of determining the powering requirement for ships. CFD uses numerical modeling to simulate the forces which act on the ship. Unlimited testing takes a fraction of the time and effort as compared to tank testing. However, it is not yet wholly proven in its accuracy. An investigation has been made using tank testing and CFD to predict the new David Pedrick Mk II Navy 44 Sail Training Crafts (STC) performance, The performance prediction process proved most accurate when using tank data to aid the CFD calculations. Using this combined method along with an aerodynamic calculation for the Mk II Navy 44 STC, a Velocity Prediction Program (VPP) was constructed. Finally, the new VPP as well as previous parametric VPPs were used to predict a full set of performance figures. These tools were also used to improve the rudder design of the Mk II Navy 44 STC.

Computational fluid dynamics was developed to the stage where it has become an indispensable part of aerospace research and design. In view of advances made in aerospace applications, the computational approach can be used for biofluid mechanics research. Several flow simulation methods developed for aerospace problems are briefly discussed for potential applications to biofluids, especially to blood flow analysis.

This paper covers the following topics in viewgraph format: purpose of data exchange standards; data exchange in engineering analysis/CFD; geometry data exchange through existing product data exchange standards, NASA Data Exchange Committee, and NASA-IGES (Initial Graphics Exchange Specification); CFD grid and solution data exchange; and data exchange for multi-disciplinary engineering.

Geometrical, flight, computational fluid dynamics (CFD), and wind-tunnel studies for the F-16XL-1 airplane are summarized over a wide range of test conditions. Details are as follows: (1) For geometry, the upper surface of the airplane and the numerical surface description compare reasonably well. (2) For flight, CFD, and wind-tunnel surface pressures, the comparisons are generally good at low angles of attack at both subsonic and transonic speeds, however, local differences are present. In addition, the shock location at transonic speeds from wind-tunnel pressure contours is near the aileron hinge line and generally is in correlative agreement with flight results. (3) For boundary layers, flight profiles were predicted reasonably well for attached flow and underneath the primary vortex but not for the secondary vortex. Flight data indicate the presence of an interaction of the secondary vortex system and the boundary layer and the boundary-layer measurements show the secondary vortex located more outboard than predicted. (4) Predicted and measured skin friction distributions showed qualitative agreement for a two vortex system. (5) Web-based data-extraction and computational-graphical tools have proven useful in expediting the preceding comparisons. (6) Data fusion has produced insightful results for a variety of visualization-based data sets.

Automation of flow field zoning in two dimensions is an important step towards reducing the difficulty of three-dimensional grid generation in computational fluid dynamics. Using a knowledge-based approach makes sense, but problems arise which are caused by aspects of zoning involving perception, lack of expert consensus, and design processes. These obstacles are overcome by means of a simple shape and configuration language, a tunable zoning archetype, and a method of assembling plans from selected, predefined subplans. A demonstration system for knowledge-based two-dimensional flow field zoning has been successfully implemented and tested on representative aerodynamic configurations. The results show that this approach can produce flow field zonings that are acceptable to experts with differing evaluation criteria.

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.

The construction of a large test facility has been proposed for simulating the blast and thermal environment resulting from nuclear explosions. This facility would be used to test the survivability and vulnerability of military equipment such as trucks, tanks and helicopters in a simulated thermal and blast environment, and to perform research into nuclear blast phenomenology. The proposed advanced design concepts, heating of driver gas and fast-acting throat valves for wave shaping, are described and the results of CFD studies to advance these new technical concepts fro simulating decaying blast waves are reported. Keywords: Computational fluid dynamics; Large blast wave simulators; Thermal simulators; CFD design studies; Blast wave simulation; LB/TS Design.

CONTENTS... Computational Fluid Dynamics - Navy Perspective; Turbulence: A Roadblock to Computational Fluid Dynamics; Computational Combustion Approaches to a Complex Phenomenon; The Emergence of Computational Ship Hydrodynamics; Computational Analysis of a Missile at a High Angle of Attack; and Profiles in Science.

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.

This study involves the development of numerical modelling in spray combustion. These modelling efforts are mainly motivated to improve the computational efficiency in the stochastic particle tracking method as well as to incorporate the physical submodels of turbulence, combustion, vaporization, and dense spray effects. The present mathematical formulation and numerical methodologies can be casted in any time-marching pressure correction methodologies (PCM) such as FDNS code and MAST code. A sequence of validation cases involving steady burning sprays and transient evaporating sprays will be included.

The needs for Computational Fluid Dynamics (CFD) in connection with student and faculty activities in the engineering departments at NPS are reviewed. Emphasis is placed on internal, propulsion related flows. Currently available CFD codes are also reviewe

Computational fluid dynamics (CFD) simulations were performed in the present study using ANSYS Fluent 18.0, a commercially available CFD package, to characterize the behaviour of the new HAWT. Static threedimensional CFD simulations were conducted. The static torque characteristics of the turbine and the simplicity of design highlight its suitability for the GE 1.5xle turbine. The major factor for generating the power through the HAWT is the velocity of air and the position of the blade angle in the HAWT blade assembly. The paper presents the effect of The blade is 43.2 m length and starts with a cylindrical shape at the root then transitions to the airfoils S818, S825 and S826 for the root, body and tip respectively. This blade also has pitch to vary as a function of radius, giving it a twist and the pitch angle at the blade tip is 4 degrees. This blade was created to be similar in size to a GE 1.5xle turbine by Cornell University. In addition, note that to represent the blade being connected to a hub, the blade root is offset from the axis of rotation by 1 meter. The hub is not included in our model. The experimental analysis of GE 1.5xle turbine, so that possible the result of CFD analysis can be compared with theoretical calculations. CFD workbench of ANSYS is used to carry out the virtue simulation and testing. The software generated test results are validated through the experimental readings. Through this obtainable result will be in the means of maximum constant power generation from HAWT.

This paper discusses the Space Shuttle Lift-off CFD model developed for potential Lift-off Debris transport for return-to-flight. The Lift-off portion of the flight is defined as the time starting with tanking of propellants until tower clear, approximately T0+6 seconds, where interactions with the launch pad cease. A CFD model containing the Space Shuttle and launch Pad geometry has been constructed and executed. Simplifications required in the construction of the model are presented and discussed. A body-fitted overset grid of up to 170 million grid points was developed which allowed positioning of the Vehicle relative to the Launch Pad over the first six seconds of Climb-Out. The CFD model works in conjunction with a debris particle transport model and a debris particle impact damage tolerance model. These models have been used to assess the interactions of the Space Shuttle plumes, the wind environment, and their interactions with each other and the Launch Pad and their ultimate effect on potential debris during Lift-off.

One or the key objectives of the Applied Research Branch in the Numerical Aerodynamic Simulation (NAS) Systems Division at NASA Allies Research Center is the accelerated introduction of highly parallel machines into a full operational environment. In this report we discuss the performance results obtained from the implementation of some computational fluid dynamics (CFD) applications on the Connection Machine CM-2 and the Intel iPSC/860. We summarize some of the experiences made so far with the parallel testbed machines at the NAS Applied Research Branch. Then we discuss the long term computational requirements for accomplishing some of the grand challenge problems in computational aerosciences. We argue that only massively parallel machines will be able to meet these grand challenge requirements, and we outline the computer science and algorithm research challenges ahead.

The application is described of computational fluid dynamics (CFD) to a hypersonic propulsion system. An overview of the problems associated with a propulsion system of this type is presented, highlighting the special role that CFD plays in the design of said systems.

The primary objective was the development of nonequilibrium radiation and chemistry models suitable for engineering applications associated with the flow fields about aeroassisted orbital transfer vehicles (AOTVs), the aero-assisted flight experiment vehicle (AFE), and other vehicles operating at superorbital velocities and very high attitudes.

The primary objective was the development of nonequilibrium radiation and chemistry models suitable for engineering applications associated with the flow fields about aeroassisted orbital transfer vehicles (AOTVs), the aero-assisted flight experiment vehicle (AFE), and other vehicles operating at superorbital velocities and very high attitudes.

Lately with the headway of thermo electric materials, direct change of warmth vitality into electrical vitality gets conceivable. Thermoelectric innovation is utilized for recuperating heat vitality loses from motor fumes gases. The force produced by thermoelectric innovation is called as thermoelectric force. In thermo electric force age a fumes heat exchanger is utilized for recouping exhaust heat and a thermo electric module is utilized for changing over warmth into power. The current examination was expected to improve the structure of fumes heat exchanger by expelling inside blades and changing the cross sectional region of warmth exchanger to conquer issue of weight drop. The structures of fumes heat exchangers considered in the past exploration works recouped most extreme warmth from the fumes of a motor However issue of weight drop or back weight was watched affecting motor execution and working. Higher back weight can break down and harm motor bringing about stoppage of motor working. Computational liquid elements CFD was utilized in the recreation of the fumes gases streaming inside the warmth exchanger. The isothermal displaying strategy was utilized in recreation procedure of the warmth exchanger. The warm reenactment is done on heat exchanger to check the surface temperature, heat move rate, and weight drop in three distinctive test conditions urban driving, rural driving and max. power driving of a vehicle with 1.2 L petroleum motor. Rectangular molded warmth exchanger was utilized in ventilation system of interior burning motor ICE is demonstrated numerically to recoup the lost warmth from motor fumes. The examination uncovered that Rectangular molded warmth exchanger with progressively expanding cross sectional region limited weight drop and achieves higher temperature and warmth move rate at the surface. The mean surface temperatures acquired after CFD examination are 459K, 555K, and 791K for the three test conditions. The weight drop for the three test conditions are 24.14 Pa, 182.5 Pa and 5.413 Kpa and that is inside as far as possible. Abhimanyu Pal | N. V. Saxena "Computational Fluid Dynamics Analysis of Exhaust Heat Exchanger for TED" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-4 | Issue-5 , August 2020, URL: https://www.ijtsrd.com/papers/ijtsrd33006.pdf Paper Url :https://www.ijtsrd.com/engineering/mechanical-engineering/33006/computational-fluid-dynamics-analysis-of-exhaust-heat-exchanger-for-ted/abhimanyu-pal

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.

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

Channel flows have three components of velocity, 1component in flow direction and 2components in spanwise of Channel. Because of heterogeneity of velocity undulations, in the channel section the vortices are formed that are nominated “Secondary Current Cells”. These cells cause the lateral shear stress in the channel walls and introduce the erosion and scour of the channel walls. Heterogeneity of the turbulency is caused due to boundary conditions of the bed, side wall and free surface, the aspect ratio and the geometry of the channel. The mechanism of secondary currents can be expressed by longitudinal vorticity equation. In this research, the flow in trapezoidal channels has been modeled using the “Computational Fluid Dynamics” (CFD) with “ANSYS CFX” soft ware, and additional to investigation of sufficiency of CFD in modeling of secondary flow cells, depth averaged velocity and boundary shear stress distributions are perused. For this purpose, the experimental model of Tominaga, and analytical model of Shiono and knight has been used to verify the numerical results. The numerical results are in agreement with the experimental and analytical models.

Motivated by progressive climate-change influence on ice degradation in caves, in this paper we present a novel methodology to investigate the link between air dynamics and ice melting. Specifically, we use surveys available for the Leupa ice cave (LIC), located in the Canin-Kanin group in the southeastern Alps and a general purpose computational fluid dynamics model (CFD). Detailed numerical simulations are evaluated on the basis of well-established approaches that consider domain, grid, boundary-conditions, turbulence closure models, buoyancy effects, porous media properties and verification with measured data. External atmospheric conditions are the main trigger for internal circulation but morphology and thermal characteristics of ice and bedrock induce a dynamical process of heat exchange ultimately responsible for ice melting. This process is generally poorly documented in real conditions. Using CFD analyses we show that both in summer and winter, warm and cold air currents within the cave are “disturbed” by several vortices and stagnation zones which locally modify the energy balance. To account for this we introduce a macroscopic physical model based on energy balance between ice surfaces and the inner ice cave airflow to determine the heat exchanged between ice and air. Using this model, a prediction of ice thickness decay over time is obtained. In the case of LIC a reduction of initial 4 cm per year is first obtained with projection of a much faster increase. The methodology is general and easily extendable to other sites, proving to be a powerful method to estimate ice evolution in caves induced by external and internal forcing.

Motivated by progressive climate-change influence on ice degradation in caves, in this paper we present a novel methodology to investigate the link between air dynamics and ice melting. Specifically, we use surveys available for the Leupa ice cave (LIC), located in the Canin-Kanin group in the southeastern Alps and a general purpose computational fluid dynamics model (CFD). Detailed numerical simulations are evaluated on the basis of well-established approaches that consider domain, grid, boundary-conditions, turbulence closure models, buoyancy effects, porous media properties and verification with measured data. External atmospheric conditions are the main trigger for internal circulation but morphology and thermal characteristics of ice and bedrock induce a dynamical process of heat exchange ultimately responsible for ice melting. This process is generally poorly documented in real conditions. Using CFD analyses we show that both in summer and winter, warm and cold air currents within the cave are “disturbed” by several vortices and stagnation zones which locally modify the energy balance. To account for this we introduce a macroscopic physical model based on energy balance between ice surfaces and the inner ice cave airflow to determine the heat exchanged between ice and air. Using this model, a prediction of ice thickness decay over time is obtained. In the case of LIC a reduction of initial 4 cm per year is first obtained with projection of a much faster increase. The methodology is general and easily extendable to other sites, proving to be a powerful method to estimate ice evolution in caves induced by external and internal forcing.

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.

The ability to enhance detonation wave transmission at a diffraction plane through various shock reflection/focusing conditions was evaluated numerically. The geometry dimensions were generally representative of the condition existing in a valve-less pulse detonation engine developed by the Naval Postgraduate School and consisted of a small cylindrical initiator combustor which transmitted a shock wave to a larger diameter combustor. The wall cross section of the larger combustor was varied to evaluate the increase in reflected shock temperature and pressure conditions ultimately revealing the dramatic increase in local temperature for a scalloped outer wall condition over the cylindrical cross section cases. The initiator diameter was held constant and the larger combustor diameters varied in order to evaluate the effects of diameter ratio on the shock reflection conditions for both cylindrical and scalloped geometries. A computational fluid dynamics (CFD) solver known as OVERFLOW was used to model the fluid dynamic processes but was limited in capability to shock wave Mach numbers less than about 4.2.

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 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 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.

Geometrical, flight, computational fluid dynamics (CFD), and wind-tunnel studies for the F-16XL-1 airplane are summarized over a wide range of test conditions. Details are as follows: (1) For geometry, the upper surface of the airplane and the numerical surface description compare reasonably well. (2) For flight, CFD, and wind-tunnel surface pressures, the comparisons are generally good at low angles of attack at both subsonic and transonic speeds, however, local differences are present. In addition, the shock location at transonic speeds from wind-tunnel pressure contours is near the aileron hinge line and generally is in correlative agreement with flight results. (3) For boundary layers, flight profiles were predicted reasonably well for attached flow and underneath the primary vortex but not for the secondary vortex. Flight data indicate the presence of an interaction of the secondary vortex system and the boundary layer and the boundary-layer measurements show the secondary vortex located more outboard than predicted. (4) Predicted and measured skin friction distributions showed qualitative agreement for a two vortex system. (5) Web-based data-extraction and computational-graphical tools have proven useful in expediting the preceding comparisons. (6) Data fusion has produced insightful results for a variety of visualization-based data sets.

An assessment was made of the impact of developments in computational fluid dynamics (CFD) on the traditional role of aerospace ground test facilities over the next fifteen years. With improvements in CFD and more powerful scientific computers projected over this period it is expected to have the capability to compute the flow over a complete aircraft at a unit cost three orders of magnitude lower than presently possible. Over the same period improvements in ground test facilities will progress by application of computational techniques including CFD to data acquisition, facility operational efficiency, and simulation of the light envelope; however, no dramatic change in unit cost is expected as greater efficiency will be countered by higher energy and labor costs.

An assessment was made of the impact of developments in computational fluid dynamics (CFD) on the traditional role of aerospace ground test facilities over the next fifteen years. With improvements in CFD and more powerful scientific computers projected over this period it is expected to have the capability to compute the flow over a complete aircraft at a unit cost three orders of magnitude lower than presently possible. Over the same period improvements in ground test facilities will progress by application of computational techniques including CFD to data acquisition, facility operational efficiency, and simulation of the light envelope; however, no dramatic change in unit cost is expected as greater efficiency will be countered by higher energy and labor costs.

An assessment was made of the impact of developments in computational fluid dynamics (CFD) on the traditional role of aerospace ground test facilities over the next fifteen years. With improvements in CFD and more powerful scientific computers projected over this period it is expected to have the capability to compute the flow over a complete aircraft at a unit cost three orders of magnitude lower than presently possible. Over the same period improvements in ground test facilities will progress by application of computational techniques including CFD to data acquisition, facility operational efficiency, and simulation of the light envelope; however, no dramatic change in unit cost is expected as greater efficiency will be countered by higher energy and labor costs.

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.

The U.S. Army Research Laboratory (ARL) has completed an initial investigation of the flow field within a typical U.S. Army Edgewood Research, Development, and Engineering Center (ERDEC) test chamber via numerical simulation. The ERDEC test chamber is designed to mix compressor-driven airflow with gas/solid effluent from a test article placed inside the chamber. An example of such a test article is a smoke generator, or smoke pot. Simulation of this flow utilized ARL computational fluid dynamics (CFD) codes that include multispecies chemical kinetics. Numerical solutions of the gas flow and effluent concentration distributions in the test chamber were generated for operating times up to 4.5 min. Numerical simulations reveal that certain values of chamber through-flow induce flow patterns within the chamber that are dominated by rotating vortices. This flow pattern increases the effluent residence time in the chamber as well as the mixing of gas/particulate from the test article with air. As a result, pockets of high effluent concentration can form in the chamber. Graphical results with discussion are presented.

The project was concerned with the development of high performance computer codes for problems in transonic aerodynamics. A practical rule to calculate the wave drag for solutions of the Euler equations was developed from an entropy equality. Symmetric shockless airfoils were analyzed for which uniqueness fails in the transonic case not just for potential flow, but also for the Euler equations.

Computational fluid dynamics calculations have been performed for a multi-body system consisting of a main missile and a number of submunitions. Numerical flow field computations have been made for various orientations and locations of submunitions using an unsteady, zonal Navier-Stokes code and the chimera composite grid discretization technique at low supersonic speeds and 0 deg angle of attack. Steady state numerical results have been obtained and compared for cases modeling six submunitions in pitch-plane symmetry and ten submunitions for which symmetry could not be exploited. Computed results show the details of the expected flow field features including the shock interactions. Computed results are compared with limited experimental data obtained for the same configuration and conditions and are generally found to be in good agreement with the data. The results help to quantify changes in the aerodynamic forces and moments, which are attributable to changes in position of the submunitions relative to one another.

Computational fluid dynamics (CFD) calculations have been performed for a multi-body system consisting of a main missile and a number of submunitions. Numerical flow field computations have been made for various orientations and locations of submunitions using an unsteady, zonal Navier-Stokes code and the chimera composite grid discretization technique at transonic speeds and zero degree angle of attack. Both steady state and unsteady numerical results have been obtained and compared for two submunitions and a missile system. Computed results show the details of the expected flow field features, including the shock interactions. Computed results are compared with limited experimental data obtained for the same configuration and conditions and are generally found to be in good agreement with the data. Comparison of the unsteady and steady state results shows an appreciable change in the aerodynamic forces and moments.

A finite difference code was implemented for the compressible Navier-Stokes equations on the Connection Machine, a massively parallel computer. The code is based on the ARC2D/ARC3D program and uses the implicit factored algorithm of Beam and Warming. The codes uses odd-even elimination to solve linear systems. Timings and computation rates are given for the code, and a comparison is made with a Cray XMP.

The Shaped Sonic Boom Demonstration project showed for the first time that by careful design of aircraft contour the resultant sonic boom can maintain a tailored shape, propagating through a real atmosphere down to ground level. In order to assess the propagation characteristics of the shaped sonic boom and to validate computational fluid dynamics codes, airborne measurements were taken of the pressure signatures in the near field by probing with an instrumented F-15B aircraft, and in the far field by overflying an instrumented L-23 sailplane. This paper describes each aircraft and their instrumentation systems, the airdata calibration, analysis of the near- and far-field airborne data, and shows the good to excellent agreement between computational fluid dynamics solutions and flight data. The flights of the Shaped Sonic Boom Demonstration aircraft occurred in two phases. Instrumentation problems were encountered during the first phase, and corrections and improvements were made to the instrumentation system for the second phase, which are documented in the paper. Piloting technique and observations are also given. These airborne measurements of the Shaped Sonic Boom Demonstration aircraft are a unique and important database that will be used to validate design tools for a new generation of quiet supersonic aircraft.