Eric L. Blades

Visualization of fluid flows in virtual environments

Visualization of Fluid Flows in Virtual Environments Ziegele , S. B. r r 1), Gopal, G. P. 1), Blades, E. 2), Moo head, R. J. 1), Marcum, D. L. 2) and Guan, Y. 1) 1) ERC GRI Visualization, Analysis and Imaging Laboratory, Mississippi State University, MS, U.S.A. E-mail : {sean | gopi | rjm | guanyl } @gri.msstate.edu 2) ERC SimCenter, Mississippi State University, MS, U.S.A., E-mail : { blades | marcum } @simcenter.msstate.edu

Numerical Simulation of a Spinning Missile with Dithering Canards Using Unstructured Grids

Euler and Navier-Stokes solutions were obtained using an unstructured-grid approach to predict the aerodynamic performance of a spinning missile with dithering canards. Integrated force and moment coefficients were computed, along with helicity contours to track the horseshoe vortices generated by the canards. Comparisons were made to determine the effect of grid resolution and viscous effects. The grid-resolution study was performed using three levels of refinement. Comparison of the viscous and inviscid force and moment coefficients revealed that the viscous effects were not significant for this low angle of attack. The largest viscous contribution was to the axial force, which was approximately 10% of the total axial force. Overall the viscous effects were minimal because the flow is supersonic and remains attached and there are no regions of separated flow where viscous effects are important. The vortices are due to the pressure difFerences acting on the canards and not due to viscous boundary-layer separation along the missile body. It was found that, at certain roll orientations, the canards do impinge on the tail fins. Solution comparisons were made to results from another high-resolution viscous flow solver and to experimental data and the results compared favorably to both.

SIMULATION OF SPINNING MISSILE FLOW FIELDS USING U 2 NCLE

Euler and Navier-Stokes solutions were obtained to predict the aerodynamic performance of a spinning missile with dithering canards. Integrated force and moment coefficients were computed, along with helicity contours to track the vortices being generated by the canards. Comparisons were made to determine the effect of grid resolution and viscous effects. The grid resolution study was performed using 3 levels of refinement. The results indicated that the force and moment coefficients generated using the medium refinement grid were in agreement with those using the fine grid. However, the finest grid increased the resolution of the vortices, particularly the canard root vortex. Comparison of the viscous and inviscid force and moment coefficients revealed that the viscous effects were not significant. The largest viscous contribution was to the axial force, which was approximately 10% of the total axial force. The main difference between the inviscid and viscous results is the resolution of the canard root vortex. Overall the viscous effects were minimal, as expected, since the flow is supersonic and at this low angle of attack, the flow remains attached, the vortices do not impinge on the tail fins or missile body, and there are no regions of separated flow where viscous effects are important.

VERIFICATION AND VALIDATION OF FORCES GENERATED BY AN UNSTRUCTURED FLOW SOLVER

A primary goal of computational fluid dynamics is the accurate prediction of the forces and moments on ships, aircraft, turbines and similar complicated geometries, especially when viscous effects are important. By using unstructured grids, much of the detail of these complicated geometries can be captured with the grid and hopefully with the solution generated by the flow solver. As unstructured flow solvers mature, the forces predicted by them should become more accurate. For unsteady maneuvering cases, the accuracy of the forces and moments is critical for accurate predictions of the location and orientation of the body in motion, because errors tend to accumulate and grow as the maneuver proceeds. Accurate simulations of maneuvers have been obtained with the structured flow solver UNCLE. However, its unstructured equivalent, U 2 NCLE, has produced anomalies that are not fully understood. In an effort to isolate and identify potential inaccuracies in the unstructured flow solver, the flow solver has undergone a thorough re-evaluation of each component and the interactions between the components. Particular attention has been paid to the effects of discretization error. The unstructured flow solver uses mixed element types to resolve the boundary, so the discretization error for the non-simplical element types was investigated. Several methods to discretize the viscous terms have been investigated, to determine whether they are linearity preserving. A new inviscid variable extrapolation method (Unstructured MUSCL) has been developed, which has a smaller discretization error than the previous method. Finally, effects of asymmetries in the grid and in the solution algorithm have been investigated.

Design and Testing of a Large Composite Asymmetric Payload Fairing

A very large asymmetric composite payload fairing (PLF) was developed for launching payloads of unconventional geometry and size on the Atlas V Heavy Lift vehicle. Currently, no launch system exists that can accommodate these payloads without requiring a redesign of the launch vehicle and/or integration facility. The asymmetric design was tailored to accommodate very large payloads while maintaining structural requirements and control authority limits of the launch vehicle as it currently stands. An optimal design was achieved through the use of an innovative computational fluid dynamics (CFD)-based geometric optimization, composite structural tailoring, and novel manufacturing methods. The design was validated through correlation with subscale wind tunnel testing, and extremely close agreement between the analysis and test was achieved. The final design resulted in a composite sandwich structure that meets or exceeds strength, buckling, flutter, thermal, and acoustic requirements and does not require significant modifications to existing launch pad integration facilities. The geometry, methods, and processes demonstrated here have wider applicability to the whole range of launch vehicle sizes and can increase the payload capabilities of each by offering fairings which are tailored specifically to existing control capability and payloads of nonstandard geometry.

Aeroelastic Effects of Spinning Missiles

.The accurate computation of forces and moments is of paramount importance in the computation of the maneuvering response of an aerospace vehicle, particularly for spinning missiles. For spinning missiles, the combination of body spin and angle of attack creates a force, called the Magnus force, at right angles to the lift vector. This force induces a moment that can perturb the dynamic stability of the missile, and flight control of the vehicle is no longer ensured. The solution for axisymmetric configurations can be predicted with steady-state algorithms. The addition of control surfaces creates an additional opposing lateral force and the flow is no longer steady and unsteady methods must be used to compute the solution. The purpose of the current work is to examine the aeroelastic effects on the aerodynamic performance of a spinning missile with dithering canards utilizing a fully-coupled computational aeroelastic approach. The nonlinearity of the flow field (e.g. moving shocks) and the complicated aerodynamic interactions at the canard- and finbody junctures necessitates the use of a computational aeroelasticity approach.

Computational-Fluid-Dynamics-Based Design Optimization of a Large Asymmetric Payload Fairing

A very large asymmetric (22×13×7  m) composite payload fairing was developed for launching payloads of unconventional geometry and size on the Atlas V Heavy Lift Vehicle. Currently, no launch system exists that can accommodate these payloads without a redesign of the launch vehicle, integration facility, or both. The asymmetric design was tailored to accommodate very large payloads while maintaining control authority limits of the launch vehicle as it currently stands. An optimal design was achieved through the expertise-guided use of an innovative computational-fluid-dynamics–based geometric optimization. The design was validated through correlation with subscale wind-tunnel testing, and extremely close agreement was achieved between the analysis and test. The final design met all design criteria and does not require significant modifications to existing launch pad integration facilities. The geometry, methods, and processes demonstrated here have wider applicability to the whole range of launch vehicle ...

Parallel Optimization Strategy for Large -Scale Computational Design

The focus of this paper is to document and demonstrate sensitivity analysis tech niques that ensure multidisciplinary flexibility , and that are utilized within a parallel optimization strategy that could possibly reduce the design costs by orders of magnitude for large -scale shape optimization requiring high -fidelity simulations. Furth ermore, unique to this optimization method, as applied to high -fidelity computational design, is the use of the second -derivative in formation produced from the Complex Taylor Series Expansion (CTSE) method. This additional information (i.e., the diagonal o f the Hessian) may be used for both design variable scaling and for incorporation into the optimization algorithm. These enhancements have been found to increase robustness and to accelerate the convergence of the optimization . Demonstrative results are sh own for a single -point aerodynamic shape optimization of a wing immersed in a transonic flow. For this relatively small scale design example with m oderately complex physics, the results illustrate that the parallel optimization strategy reduced the total d esign time by an order of magnitude . For larger scale design and/or optimizations where the high -fidelity physics require much more CPU time, the savings will become much more pronounce

Visualization of Fluid Flows in Virtual Environments

As computational methods keep improving and computational resources are entering a new era, the solution to physical problems is available at very high resolutions. Unfortunately, the computational resources that are available for interactive visualization of the solution at this resolution are not as accessible, hence the need to resort to alternative display techniques which can portray a better understanding of the solution, even at a lesser resolution. In this paper, we discuss methods for visualizing fluid data in a virtual environment. For steady-state data sets, we employ a feature-based streamline seeding technique. For time-variant data sets, we utilize view-dependent seeded pathlines. These methods address the aforementioned problems with high resolution data sets. In addition, we present the advantages of using virtual environments for flow visualization, and how analysts benefit from these advantages.© 2003 ASME