Downloads & Free Reading Options - Results

This article is from Neurointervention , volume 9 . Abstract Despite recent development of computational fluid dynamics (CFD) research, analysis of computational fluid dynamics of cerebral vessels has several limitations. Although blood is a non-Newtonian fluid, velocity and pressure fields were computed under the assumptions of incompressible, laminar, steady-state flows and Newtonian fluid dynamics. The pulsatile nature of blood flow is not properly applied in inlet and outlet boundaries. Therefore, we present these technical limitations and discuss the possible solution by comparing the theoretical and computational studies.

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.

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:

The project focused on depth-integrated modeling of coastal wave and surf-zone processes in support of computational fluid dynamics (CFD) simulation of ship motions. There were two components of the project involving two MS and one PhD candidate under the guidance of the principal investigator. The first was the development of a numerical dispersion relation for a family of Boussinesq-type equations commonly used in modeling of coastal wave transformation. The relation depicts numerical dissipation and dispersion in wave propagation and provides guidelines for model setup in terms of temporal and spatial discretization. The second component was an extension of existing depth-integrated wave models to describe overtopping of coastal reefs and structures along with series of CFD and laboratory experiments for model validation. The basic approach utilizing the HLLS Riemann solver performs reasonably well and produces stable and efficient numerical results for practical application. Although the two components were performed separately, they both contribute to improved capabilities in modeling of the coastal wave environment that can provide input to three-dimensional seakeeping analysis.

Implicit finite differences schemes are often the preferred numerical schemes in computational fluid dynamics, requiring less stringent stability bounds than the explicit schemes. Each iteration in an implicit scheme, however, involves global data dependencies in the form of second and higher order recurrences. Efficient parallel implementations of such iterative methods, therefore, are considerably more difficult and non-intuitive. In this paper, we consider the parallelization of the implicit schemes that are used for solving the Euler and the thin layer Navier-Stokes equations and that require inversions of large linear systems in the form of block tri-diagonal and/or block penta- diagonal matrices. We focus our attention on three-dimensional cases an present schemes that minimize the total execution time. We describe partitioning and scheduling schemes for alleviating the effects of the global data dependencies. An analysis of the communication and the computation aspects of these methods is presented. The effect of the boundary conditions on the parallel schemes is also discussed. The ARC-3D code, developed at NASA Ames, is used as an example application. Performance of the proposed methods is verified on the Victor multiprocessor system which is a message passing architecture developed at the IBM, T.J. Watson Research Center. (KR)

The Design Analysis Branch (NE-Ml) at the Kennedy Space Center has not had the ability to accurately couple Rigid Body Dynamics (RBD) and Computational Fluid Dynamics (CFD). OVERFLOW-D is a flow solver that has been developed by NASA to have the capability to analyze and simulate dynamic motions with up to six Degrees of Freedom (6-DOF). Two simulations were prepared over the course of the internship to demonstrate 6DOF motion of rigid bodies under aerodynamic loading. The geometries in the simulations were based on a conceptual Space Launch System (SLS). The first simulation that was prepared and computed was the motion of a Solid Rocket Booster (SRB) as it separates from its core stage. To reduce computational time during the development of the simulation, only half of the physical domain with respect to the symmetry plane was simulated. Then a full solution was prepared and computed. The second simulation was a model of the SLS as it departs from a launch pad under a 20 knot crosswind. This simulation was reduced to Two Dimensions (2D) to reduce both preparation and computation time. By allowing 2-DOF for translations and 1-DOF for rotation, the simulation predicted unrealistic rotation. The simulation was then constrained to only allow translations.

Spacecraft thermal protection systems are at risk of being damaged due to airflow produced from

Some recent developments in acceleration of convergence methods for vector sequences are reviewed. The methods considered are the minimal polynomial extrapolation, the reduced rank extrapolation, and the modified minimal polynomial extrapolation. The vector sequences to be accelerated are those that are obtained from the iterative solution of linear or nonlinear systems of equations. The convergence and stability properties of these methods as well as different ways of numerical implementation are discussed in detail. Based on the convergence and stability results, strategies that are useful in practical applications are suggested. Two applications to computational fluid mechanics involving the three dimensional Euler equations for ducted and external flows are considered. The numerical results demonstrate the usefulness of the methods in accelerating the convergence of the time marching techniques in the solution of steady state problems.

The aerospace plane design challenge is presented in the form of the view-graphs. The following topics are included: the CFD design technology development; CFD validation vs. measurable fluid dynamics validation; and discussion of results.

This paper describes and discusses the textbook, Fundamentals of Computational Fluid Dynamics by Lomax, Pulliam, and Zingg, which is intended for a graduate level first course in computational fluid dynamics. This textbook emphasizes fundamental concepts in developing, analyzing, and understanding numerical methods for the partial differential equations governing the physics of fluid flow. Its underlying philosophy is that the theory of linear algebra and the attendant eigenanalysis of linear systems provides a mathematical framework to describe and unify most numerical methods in common use in the field of fluid dynamics. Two linear model equations, the linear convection and diffusion equations, are used to illustrate concepts throughout. Emphasis is on the semi-discrete approach, in which the governing partial differential equations (PDE's) are reduced to systems of ordinary differential equations (ODE's) through a discretization of the spatial derivatives. The ordinary differential equations are then reduced to ordinary difference equations (O(Delta)E's) using a time-marching method. This methodology, using the progression from PDE through ODE's to O(Delta)E's, together with the use of the eigensystems of tridiagonal matrices and the theory of O(Delta)E's, gives the book its distinctiveness and provides a sound basis for a deep understanding of fundamental concepts in computational fluid dynamics.

In this paper we describe the parallelization of the multi-zone code versions of the NAS Parallel Benchmarks employing multi-level OpenMP parallelism. For our study we use the NanosCompiler, which supports nesting of OpenMP directives and provides clauses to control the grouping of threads, load balancing, and synchronization. We report the benchmark results, compare the timings with those of different hybrid parallelization paradigms and discuss OpenMP implementation issues which effect the performance of multi-level parallel applications.

The current compute environment that most researchers are using for the calculation of 3D unsteady Computational Fluid Dynamic (CFD) results is a super-computer class machine. The Massively Parallel Processors (MPP's) such as the 160 node IBM SP2 at NAS and clusters of workstations acting as a single MPP (like NAS's SGI Power-Challenge array and the J90 cluster) provide the required computation bandwidth for CFD calculations of transient problems. If we follow the traditional computational analysis steps for CFD (and we wish to construct an interactive visualizer) we need to be aware of the following: (1) Disk space requirements. A single snap-shot must contain at least the values (primitive variables) stored at the appropriate locations within the mesh. For most simple 3D Euler solvers that means 5 floating point words. Navier-Stokes solutions with turbulence models may contain 7 state-variables. (2) Disk speed vs. Computational speeds. The time required to read the complete solution of a saved time frame from disk is now longer than the compute time for a set number of iterations from an explicit solver. Depending, on the hardware and solver an iteration of an implicit code may also take less time than reading the solution from disk. If one examines the performance improvements in the last decade or two, it is easy to see that depending on disk performance (vs. CPU improvement) may not be the best method for enhancing interactivity. (3) Cluster and Parallel Machine I/O problems. Disk access time is much worse within current parallel machines and cluster of workstations that are acting in concert to solve a single problem. In this case we are not trying to read the volume of data, but are running the solver and the solver outputs the solution. These traditional network interfaces must be used for the file system. (4) Numerics of particle traces. Most visualization tools can work upon a single snap shot of the data but some visualization tools for transient problems require dealing with time.

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.

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.

This report describes an overview of the research efforts undertaken to develop a computational fluid dynamics (CFD) tool to analyze flow fields relevant to chemical oxygen/iodine lasers (COIL). In the listed references, computations of the three-dimensional nozzle flow fields with transverse jet injection are described in addition to several two-dimensional computational results, verifying the implementation of the model equations. Improvement in the efficiency of the computations was demonstrated by the use of a grid sequencing approach. (7 refs.)

Algorithm development. Implementation of a 3-D Navier Stokes implicit research code for AFFDL was initiated. This required the parallel solution of block-tridiagonal system and so was more challenging than the above explicit code. This is being continued in a new AFOSR grant. Connection Machine experiments. To keep abreast of SIMD architecture performance, a series of Fortran and C kerrels were studies on the Argonne Laboratory CM-2 during the summer of 1989. It was concluded that the available Fortran 8X implementation of the CM-2 was too inefficient to warrant continued at that time. Keywords: Programming languages; Computer programming; Computer architecture.

This research concerns projects of seven investigators at the University of Pittsburgh relating to the general area of computational fluid dynamics. Topics include the dual variable method, Differential Algebraic Equation, the reduced basis method, divergence free finite elements, diffusive- transport systems, and bifurcation phenomena. Short descriptions of these projects are included, along with references to published reports. (jg)

This research concerned three independent projects of ICMA (Institute of Computational Mathematics and Applications) personnel, each belonging to the general area of computational fluid dynamics. The first project dealt with the computation of stationary Navier-Stokes solutions using continuation methods. Error estimates for certain finite element solutions of continuation problems were derived and extensions to more general operators including the Navier-Stokes operator were investigated. Numerical methods for the detection of Hopf bifurcation were studied. The second project involved construction, analysis and implementation of efficient computer algorithms for the finite difference and finite element-dual variable discretization of the two-dimensional Navier-Stokes problems. Particular attention was given to finite element and finite differences discretization such problems that arise in combustor modeling. The third project sought to extend the dual variable reduction technique to various fluid models. This required the construction of a network analogue for the discrete difference equations along with an analysis of the fundamental matrix and dual variable transformation involved. (Author)

Quantum-computing ideas are applied to the practical and ubiquitous problem of fluid dynamics simulation. Hence, this paper addresses two separate areas of physics: quantum mechanics and fluid dynamics (or specifically, the computational simulation of fluid dynamics). The quantum algorithm is called a quantum lattice gas. An analytical treatment of the microscopic quantum lattice-gas system is carried out to predict its behavior at the mesoscopic scale. At the mesoscopic scale, a lattice Boltzmann equation with a nonlocal collision term that depends on the entire system wave function, governs the dynamical system. Numerical results obtained from an exact simulation of a one-dimensional quantum lattice model are included to illustrate the formalism. A symbolic mathematical method is used to implement the quantum mechanical model on a conventional work- station The numerical simulation indicates that classical viscous damping is not present in the one-dimensional quantum lattice-gas system.

No Description

Computational Fluid Dynamics (CFD) has been used in recent applications to affect subcomponent designs in liquid propulsion rocket engines. This paper elucidates three such applications for turbine stage, pump stage, and combustor chamber geometries. Details of these applications include the development of a high turning airfoil for a gas generator (GG) powered, liquid oxygen (LOX) turbopump, single-stage turbine using CFD as an integral part of the design process. CFD application to pump stage design has emphasized analysis of inducers, impellers, and diffuser/volute sections. Improvements in pump stage impeller discharge flow uniformity have been seen through CFD optimization on coarse grid models. In the area of combustor design, recent CFD analysis of a film cooled ablating combustion chamber has been used to quantify the interaction between film cooling rate, chamber wall contraction angle, and geometry and their effects of these quantities on local wall temperature. The results are currently guiding combustion chamber design and coolant flow rate for an upcoming subcomponent test. Critical aspects of successful integration of CFD into the design cycle includes a close-coupling of CFD and design organizations, quick turnaround of parametric analyses once a baseline CFD benchmark has been established, and the use of CFD methodology and approaches that address pertinent design issues. In this latter area, some problem details can be simplified while retaining key physical aspects to maintain analytical integrity.

Lectures from the National Programme on Technology Enhanced Learning - Mechanical Engineering - Computational Fluid Dynamics

This collection of papers was presented at the Computational Fluid Dynamics (CFD) Conference held at Ames Research Center in California on March 12 through 14, 1991. It is an overview of CFD activities at NASA Lewis Research Center. The main thrust of computational work at Lewis is aimed at propulsion systems. Specific issues related to propulsion CFD and associated modeling will also be presented. Examples of results obtained with the most recent algorithm development will also be presented.

This collection of papers was presented at the Computational Fluid Dynamics (CFD) Conference held at Ames Research Center in California on March 12 through 14, 1991. It is an overview of CFD activities at NASA Lewis Research Center. The main thrust of computational work at Lewis is aimed at propulsion systems. Specific issues related to propulsion CFD and associated modeling will also be presented. Examples of results obtained with the most recent algorithm development will also be presented.

This collection of papers was presented at the Computational Fluid Dynamics (CFD) Conference held at Ames Research Center in California on March 12 through 14, 1991. It is an overview of CFD activities at NASA Lewis Research Center. The main thrust of computational work at Lewis is aimed at propulsion systems. Specific issues related to propulsion CFD and associated modeling will also be presented. Examples of results obtained with the most recent algorithm development will also be presented.

This collection of papers was presented at the Computational Fluid Dynamics (CFD) Conference held at Ames Research Center in California on March 12 through 14, 1991. It is an overview of CFD activities at NASA Lewis Research Center. The main thrust of computational work at Lewis is aimed at propulsion systems. Specific issues related to propulsion CFD and associated modeling will also be presented. Examples of results obtained with the most recent algorithm development will also be presented.

A study was conducted to evaluate the accuracy of a commercial computational fluid dynamics (CFD) code (CFDRC-ACE+) for predicting incompressible air jet flows with simple geometries. Specifically, the axis- symmetric and two-dimensional heated air-jets were simulated using a standard k- epsilon turbulence model. These CFD predictions were directly compared to an extensive compilation of experimental data from archive literature. The round jet results indicated that the code over-predicted the velocity-spreading rate by 24% and the temperature spreading rate by 29%

Incompressible two-dimensional flows such as the advection (Liouville) equation and the Euler equations have a large family of conservation laws related to conservation of area. We present two Eulerian numerical methods which preserve a discrete analog of area. The first is a fully discrete model based on a rearrangement of cells; the second is more conventional, but still preserves the area within each contour of the vorticity field. Initial tests indicate that both methods suppress the formation of spurious oscillations in the field.

A finite element method for solving nonlinear differential equations on a grid, with potential applicability to computational fluid dynamics (CFD), is developed and tested. The current method facilitates the computation of solutions of a high polynomial degree on a grid. A high polynomial degree is achieved by interpolating both the value, and the value of the derivatives up to a given order, of continuously distributed unknown variables. The two-dimensional lid-driven cavity, a common benchmark problem for CFD methods, is used as a test case. It is shown that increasing the polynomial degree has some advantages, compared to increasing the number of grid-points, when solving the given benchmark problem using the current method. The current method yields results which agree well with previously published results for this test case.

NAS 1.55:10038-Vol-2 Digitized from IA1177307-08-0020 , IA1177307-08-0021 , IA1177307-08-0022 , IA1177307-08-0023 , IA1177307-08-0024 , IA1177307-08-0025 .

Image L88-6867 is available as an electronic file from the photo lab. See URL. -- Color graphic CAD CFD model of the National Aerospace Plane.

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.

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.

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.

The Air Force SEEK EAGLE Office (AFSEO), Eglin Air Force Base (AFB), FL, is the United States Air Force (USAF) authority for weapons certification efforts. AFSEO performs test and evaluation for aircraft/store compatibility certification and uses Computational Fluid Dynamics (CFD) to support this process. Determining the flow about an aircraft/store combination can be extremely difficult. Complicated geometry such as pylons, launchers, and internal weapons bays can create severe acoustic and aerothermodynamic environments, which are challenging to numerically simulate. The additional challenge of rapidly and accurately simulating the trajectory of a store separation in a high-volume simulation environment is beyond the capabilities of most CFD programs. The USAF requirement for numerous, simultaneous and quick-reaction solutions for a wide variety of stores and aircraft can only be accomplished through application of parallel high-performance computing resources that meet the significant computational and memory demands of the various cases.

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.

Computational fluid dynamics (CFD) is necessary in the design processes of all current aerospace plane programs. Single-stage-to-orbit (STTO) aerospace planes with air-breathing supersonic combustion are going to be largely designed by means of CFD. The challenge of the aerospace plane design is to provide credible CFD results to work from, to assess the risk associated with the use of those results, and to certify CFD codes that produce credible results. To establish the credibility of CFD results used in design, the following topics are discussed: CFD validation vis-a-vis measurable fluid dynamics (MFD) validation; responsibility for credibility; credibility requirement; and a guide for establishing credibility. Quantification of CFD uncertainties helps to assess success risk and safety risks, and the development of CFD as a design tool requires code certification. This challenge is managed by designing the designers to use CFD effectively, by ensuring quality control, and by balancing the design process. For designing the designers, the following topics are discussed: how CFD design technology is developed; the reasons Japanese companies, by and large, produce goods of higher quality than the U.S. counterparts; teamwork as a new way of doing business; and how ideas, quality, and teaming can be brought together. Quality control for reducing the loss imparted to the society begins with the quality of the CFD results used in the design process, and balancing the design process means using a judicious balance of CFD and MFD.

NAS 1.55:3078 Digitized from IA1177307-04-0045 , IA1177307-04-0046 , IA1177307-04-0047 , IA1177307-04-0048 , IA1177307-04-0098 , IA1177307-04-0049 , IA1177307-04-0050 , IA1177307-04-0051 .

NAS 1.55:3078 Digitized from IA1177307-04-0045 , IA1177307-04-0046 , IA1177307-04-0047 , IA1177307-04-0048 , IA1177307-04-0098 , IA1177307-04-0049 , IA1177307-04-0050 , IA1177307-04-0051 .

The Unsteady Reynolds-Averaged Navier Stokes (URANS) approach applied in conjunction with the Eddy Interaction Model (EIM) is used here to conduct numerical simulations of aerosol particle deposition on the human form. Numerical simulation of a two-phase turbulent impinging jet flow is studied to validate the proposed methodology. The numerical deposition results are compared with some relevant experimental measurements. The results of this validation show that the standard EIM with turbulent tracking tends to over predict the deposition efficiency. Greatly improved results were achieved by using a near-wall correction with the EIM. After the validation of the methodology, a number of detailed numerical simulations of aerosol particle deposition on a human form were conducted. Simulations were conducted for 13 aerosol particle sizes ranging from 0.1 to 40 micrometers. For each of these particle sizes, three orientations of the human form relative to the incident wind direction were simulated (viz., with the human form oriented 0, 90 and 180 degrees with respect to the direction of the incident wind). High-resolution isopleths of the deposition probability on the surface of the human form are presented. To provide the quantitative information for future applications by researchers, extensive data files have been produced, providing information on the cell area for each triangle used in the tessellation of the surface of the human form, the associated body part associated with this triangular cell, and the computed deposition probability associated the triangular cell.

In the spirit of the Air Force Office of Scientific Research's (AFOSR) initiative to promote University-Industry Collaborative Research, a collaborative project entitled, Hybrid Techniques in Computational Fluid Dynamics (CFD) has been executed by the National Science Foundation Engineering Research Center for Computational Field Simulation (NSF ERC) at Mississippi State University. The industrial participants include McDonnell Douglas Company, Boeing Company, and Teledyne Brown Engineering Company. The research and development activities of this effort are focused on the advancement of methodologies to increase the efficiency, quality, and productivity of an overall CFD simulation associated with geometrically complex configurations. The progress realized in the aforementioned development is presented in this final report. Progress concerning efforts designed to improve the efficiency and applicability of the CFD to geometrically complex configurations utilizing hybrid techniques is presented. This progress has been brought about through the developments and enhancements in hybrid grid generation methodology and solution algorithms for associated Euler and Navier-Stokes equations. In particular, the enhancement of the two and three dimensional hybrid grid system and CFD simulation solver is presented. The development of the three dimensional hybrid grid system and solution system allowing viscous effects with complex examples is presented to demonstrate the success of these methodologies.

The first and largest color Sun 3/160C in the CFD workstation network was purchased with funds made available through this grant. This workstation has been used as a server and general computational node, as well as a workstation. Research Projects: Development of Adaptive Grid Schemes based on Poisson Grid Generators; A Zonal Method for Extending the Applicability of the Parabolized Navier Stokes Equations; and Numerical Simulation of Helicopter Rotor Flowfields.

The multidisciplinary nature of rotary-wing aeromechanics poses a daunting challenge for the design of practical modeling and simulation software that is accurate, efficient, and maintainable. This paper describes the design strategy for the US Army's Helios software, which features a lightweight Python-language integration framework combined with well-defined interfaces to link together various multidisciplinary software components. This design facilitates the use of alternative component software within Helios, the addition of new component software into Helios, and the rapid introduction of new computational fluid dynamics technology within Helios. This paper also presents examples of Helios rotary-wing aeromechanics simulations that include simultaneous solutions for rotor dynamics and aerodynamics plus high resolution of the rotor wake system.

Accurate modeling of near-field wave propagation is critical to determine blast wave overpressure of large caliber muzzle brakes. Experimental testing to determine blast overpressure is costly, making computational fluid dynamics (CFD) simulations of these flow-fields a viable alternative. Techniques and specialized CFD codes are being developed in order to properly model the unsteady, very high-pressure flows of gun muzzle blast. Two CFD codes, Fluent 6.1.11 (a prerelease version of Fluent) and the Discontinuous Galerkin Code (DG) were developed at Rensselaer Polytechnic Institute, Troy, NY. These codes were used to compare experimental shadowgraph data from the 7.62-mm NATO rifle G3 using a DM-41 training round for the purpose of developing CFD modeling techniques and validation of the CFD codes. Unsteady grid adaption was used with both solvers in order to reduce solution error near unsteady blast waves and shocks. It is possible to get good results from Fluent with high levels of adaption, however DG can model blast with courser grid adaption. It was also found that DG required an order-of-magnitude longer solution time than Fluent for a given number of grid elements. The 7.62-mm NATO G3 CFD precursor flow results matched experimental shadowgraph results well, however, the main propellant flow results did not match well.

The Maritime Platforms Division within DSTO is currently studying the science and technology of autonomous underwater vehicles for defence applications. Part of this work involves a study of the hydrodynamics and maneuverability of these vehicles and the development of methods to determine the hydrodynamic coefficients of submerged bodies as a function of their shape. This report describes the application of the FIDAP Computational Fluid Dynamics package to the calculation of lift and drag forces on relatively simple underwater vehicle shapes, including cylinders, spheres, flat plates, and wing profiles. The degree to which FIDAP accurately reproduces known experimental data on these shapes is described and the applicability of other Computational Fluid Dynamics packages is discussed. (13 tables, 2 figures, 38 refs.)

The Maritime Platforms Division within DSTO is currently studying the science and technology of autonomous underwater vehicles for defence applications. Part of this work involves a study of the hydrodynamics and maneuverability of these vehicles and the development of methods to determine the hydrodynamic coefficients of submerged bodies as a function of their shape. This report describes the application of the FIDAP Computational Fluid Dynamics package to the calculation of lift and drag forces on relatively simple underwater vehicle shapes, including cylinders, spheres, flat plates, and wing profiles. The degree to which FIDAP accurately reproduces known experimental data on these shapes is described and the applicability of other Computational Fluid Dynamics packages is discussed. (13 tables, 2 figures, 38 refs.)

ebook for CFD

Three examples of response surface modeling with CFD are presented for combined cycle propulsion components. The examples include a mixed-compression-inlet during hypersonic flight, a hydrogen-fueled scramjet combustor during hypersonic flight, and a ducted-rocket nozzle during all-rocket flight. Three different experimental strategies were examined, including full factorial, fractionated central-composite, and D-optimal with embedded Plackett-Burman designs. The response variables have been confined to integral data extracted from multidimensional CFD results. Careful attention to uncertainty assessment and modeling bias has been addressed. The importance of automating experimental setup and effectively communicating statistical results are emphasized.

This viewgraph presentation gives an overview of the parallel domain decomposition preconditioning for computational fluid dynamics. Details are given on some difficult fluid flow problems, stabilized spatial discretizations, and Newton's method for solving the discretized flow equations. Schur complement domain decomposition is described through basic formulation, simplifying strategies (including iterative subdomain and Schur complement solves, matrix element dropping, localized Schur complement computation, and supersparse computations), and performance evaluation.

A systematic approach is presented for developing entropy stable (SS) formulations of any order for the Navier-Stokes equations. These SS formulations discretely conserve mass, momentum, energy and satisfy a mathematical entropy inequality. They are valid for smooth as well as discontinuous flows provided sufficient dissipation is added at shocks and discontinuities. Entropy stable formulations exist for all diagonal norm, summation-by-parts (SBP) operators, including all centered finite-difference operators, Legendre collocation finite-element operators, and certain finite-volume operators. Examples are presented using various entropy stable formulations that demonstrate the current state-of-the-art of these schemes.