No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Flow Field Characterization of a Generic High-Speed Projectile Configuration
This paper discusses effects of high-frequency damping on iterative convergence of an implicit defect-correction solver for viscous problems. The study targets a finite-volume discretization with a one parameter family of damped viscous schemes. The parameter α controls high-frequency damping: zero damping with , and larger damping for larger . Convergence rates are predicted for a model diffusion equation by a Fourier analysis over a practical range of α. It is shown that the convergence rate attains its minimum at on regular quadrilateral grids, and deteriorates for larger values of α. A similar behavior is observed for regular triangular grids. In both quadrilateral and triangular grids, the solver is predicted to diverge for α smaller than approximately 0.5. Numerical results are shown for the diffusion equation and the Navier-Stokes equations on regular and irregular grids. The study suggests that and 4/3 are suitable values for robust and efficient computations, and is recommended for the diffusion equation, which achieves higher-order accuracy on regular quadrilateral grids. Finally, a Jacobian-Free Newton-Krylov solver with the implicit solver (a low-order Jacobian approximately inverted by a multi-color Gauss-Seidel relaxation scheme) used as a variable preconditioner is recommended for practical computations, which provides robust and efficient convergence for a wide range of α.
A detailed description of the quantification of uncertainties for the Ares I ascent aero 6-DOF wind tunnel database is presented. The database was constructed from wind tunnel test data and CFD results. The experimental data came from tests conducted in the Boeing Polysonic Wind Tunnel in St. Louis and the Unitary Plan Wind Tunnel at NASA Langley Research Center. The major sources of error for this database were: experimental error (repeatability), database modeling errors, and database interpolation errors.
A combined experimental and numerical study was conducted on a generic projectile configuration with low-aspect-ratio fins. The main objectives of this study were to characterize the aerodynamic behavior and validate numerical simulations for a range of Mach numbers (0.4–4) to facilitate an understanding of major flow features such as forebody and fin-generated shock waves, crossflow shear layer vortex, and fin vortex interactions. Measurements included forces and moments, surface oil flow visualization, and high-speed shadowgraph imaging. Numerical simulations were performed using the CFD++ solver. The results showed an excellent match between the experimental and numerical force and moment data. Pressure contours obtained using numerical simulations were integrated to obtain the contributions of individual components toward the total normal force on the body. Flow visualization results show a few complex and interesting flow features, such as shear layer roll-up, crossflow and fin tip vortex interactions, and shock-wave–boundary-layer interactions. The effects of vortex strength and location were analyzed to determine their contributions to the overall forces on the model. The database generated will be very useful for further validation of the numerical tool and a better understanding of vortex-dominated supersonic flows.
View Video Presentation: https://doi.org/10.2514/6.2022-1174.vid Details of the high speed form of the Spalart-Allmaras turbulence model and the Menter turbulence model incorporated into the Kestrel KCFD unstructured finite volume CFD solver and the SAMAir Cartesian CFD solver have been presented. These turbulence models include compressibility corrections, automatic wall functions, and RANS/LES (DDES) options. Example RANS applications of both models have been presented. The compressible SSTM turbulence model produced the best overall results for the set of test cases presented here.
View Video Presentation: https://doi.org/10.2514/6.2021-2607.vid An experimental study involving force and moment measurements, high-speed shadowgraphy, and surface oil flow visualization was conducted on a generic axisymmetric projectile configuration with low aspect-ratio fins at the Florida State University Polysonic Wind Tunnel. The main objectives of this study were to validate numerical simulations and generate an aerodynamic database for a range of Mach numbers (0.4 to 4) and control surface deflections. Results showed an excellent match between the experimental and numerical data for the baseline configuration. Surface oil flow visualization and shadowgraph images showed a few complex and interesting flow features such as body vortex and fin interactions, shock-shock, and shock-boundary layer interactions. Control surfaces were very effective for pitch and roll control at all Mach numbers and control deflections tested. The database generated will be very useful for further validation of the numerical tool and the design of control laws.
A computational investigation was performed to determine the aerodynamic coefficients dependence on roll orientation for a low aspect ratio finned projectile. Navier-Stokes (CFD++) and inviscid (Cart3D) computational fluid dynamics flow solvers were used to characterize the aerodynamics of the flight vehicle. The results suggest that viscous flow phenomena becomes relevant when the lifting fins are oriented leeward on the projectile at moderate to high angles of attack. In order to improve our understanding of the flow physics associated with the observed phenomena, the generation and advection of the vortical flow structures produced by the fins were studied.
This chapter describes the design and features of a visualization tool called ParaView, a tool that allows scientists to visualize and analyze extremely large datasets. The tool provides a graphical user interface for the creation and dynamic execution of visualization tasks. ParaView transparently supports the visualization and rendering of large datasets by executing these programs in parallel on shared or distributed memory machines. ParaView supports hardware-accelerated parallel rendering and achieves interactive rendering performance via level-of-detail techniques. The design balances and integrates a number of diverse requirements, including the ability to handle large data, ease of use, and extensibility by developers. The chapter describes the requirements that guided the design, identifies the importance of those requirements to scientific users, and discusses key design decisions and tradeoffs.
The near-field behavior of a wingtip vortex flow has been studied computationally and experimentally in an interactive fashion, The computational approach involved using the method of artificial compressibility to solve the three-dimensional, incompressible, Navier-Stokes equations with experimentally determined boundary conditions and a modified Baldwin-Barth turbulence model. Inaccuracies caused by the finite difference technique, grid resolution, and turbulence modeling have been explored. The complete geometry case was computed using 1.5 million grid points and compared with mean velocity measurements on the suction side of the wing and in the near wake. Good agreement between the computed and measured flowfields has been obtained. The velocity distribution in the vortex core compares to within 3% of the experiment.
Two new two-equation eddy-viscosity turbulence models will be presented. They combine different elements of existing models that are considered superior to their alternatives. The first model, referred to as the baseline (BSL) model, utilizes the original k-omega model of Wilcox In the inner region of the boundary layer and switches to the standard k -epsilon model in the outer region and in free shear flows. It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity. The second model results from a modification to the definition of the eddy-viscosity in the BSL model, which accounts for the effect of the transport of the principal turbulent shear stress. The new model is called the shear-stress transport-model and leads to major improvements in the prediction of adverse pressure gradient flows.
Aerodynamic Dataset Generation of a Long-Range Projectile
- J D Vasile
- J T Bryson
- J Sahu
- J L Paul
- B C Gruenwald
- Pokela R.