Publications

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A brief overview of Sandia National Laboratories will be presented highlighting the mission of Engineering Science Center. The Engineering Science Center provides a wide range of capabilities to support the lab's missions. As part of the Engineering Science Center the Aeroscience department provides research, development and application expertise in both experimental and computation compressible fluid mechanics. The role of Aeroscience at Sandia National Labs will be discussed with a focus on current research and development activities within the Aeroscience Department. These activities will be presented within the framework of a current program to highlight the synergy between computational and experimental work. The research effort includes computational and experimental activities covering fluid and structural dynamics disciplines. The presentation will touch on: probable excitation sources that yield the level of random vibration observed during flight; the methods that have been developed to model the random pressure fields in the turbulent boundary layer using a combination of CFD codes and a model of turbulent boundary layer pressure fluctuations; experimental measurement of boundary layer fluctuations; the methods of translating the random pressure fields to time-domain spatially correlated pressure fields.

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Steady-state Reynolds-averaged Navier-Stokes (RANS) simulations are presented for the three-dimensional flow over a simplified tractor/trailer geometry at zero degrees yaw angle. The simulations are conducted using a multi-block, structured computational fluid dynamics (CFD) code. The turbulence closure model employed is the two-equation Menter k-ω model. The discretization error is estimated by employing two grid levels: a fine mesh of 20 million cells and a coarser mesh of 2.5 million cells. Simulation results are compared to experimental data obtained at the NASA-Ames 7 × 10 ft wind tunnel. Quantities compared include vehicle drag, surface pressures, and time-averaged velocities in the trailer near wake. The results indicate that the RANS approach is able to accurately predict the surface pressure on the vehicle, with the exception of the base region. The pressure predictions in the base region are poor due to the inability of the RANS model to accurately capture the near-wake vortical structure. However, the gross pressure levels in the base region are in reasonable agreement with experiment, and thus the overall vehicle drag is well predicted. Copyright © 2006 by ASME.

Methods for analysis of fluid-structure interaction using high fidelity simulations are critically reviewed. First, a literature review of modern numerical techniques for simulation of aeroelastic phenomena is presented. The review focuses on methods contained within the arbitrary Lagrangian-Eulerian (ALE) framework for coupling computational fluid dynamics codes to computational structural mechanics codes. The review treats mesh movement algorithms, the role of the geometric conservation law, time advancement schemes, wetted surface interface strategies, and some representative applications. The complexity and computational expense of coupled Navier-Stokes/structural dynamics simulations points to the need for reduced order modeling to facilitate parametric analysis. The proper orthogonal decomposition (POD)/Galerkin projection approach for building a reduced order model (ROM) is presented, along with ideas for extension of the methodology to allow construction of ROMs based on data generated from ALE simulations.

An experiment was conducted in Arnold Engineering Development Center's 16-ft transonic wind tunnel to measure the dependency of vortex-induced counter torque upon J (the ratio of spin motor jet dynamic pressure to freestream dynamic pressure), Mach number, Reynolds number, angle of attack and roll orientation, spin motor nozzle configuration, and fin cant angle. Counter torque data and Laser Vapor Screen images confirm that J is the dominant parameter for correlating counter torque produced by a given vehicle configuration, flight condition, angle of attack and roll orientation. At M = 0.8 (with no shock waves in the flow), we observed a monotonie variation of the counter torque coefficient CCT with J that is independent of Reynolds number but dependent on angle of attack and the orientation of the fins with respect to the spin motor nozzle azimuthal location. At M = 0.95 and 1.1, measured values of CCT were strongly influenced by changes in Reynolds number, suggesting that shock-boundary layer interaction may be present.

The Detached Eddy Simulation (DES) and steadystate Reynolds-Averaged Navier-Stokes (RANS) turbulence modeling approaches are examined for the incompressible flow over a square cross-section cylinder at a Reynolds number of 21,400. A compressible flow code is used which employes a second-order Roe upwind spatial discretization. Efforts are made to assess the numerical accuracy of the DES predictions with regards to statistical convergence, iterative convergence, and temporal and spatial discretization error. Three-dimensional DES simulations compared well with two-dimensional DES simulations, suggesting that the dominant vortex shedding mechanism is effectively two-dimensional. The two-dimensional simulations are validated via comparison to experimental data for mean and RMS velocities as well as Reynolds stress in the cylinder wake. The steady-state RANS models significantly overpredict the size of the recirculation zone, thus underpredicting the drag coefficient relative to the experimental value. The DES model is found to give good agreement with the experimental velocity data in the wake, drag coefficient, and recirculation zone length.

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