Publications

In this study, we extend self-similar, far-field, turbulent wake concepts to estimate the 2-d drag coefficient for a range of bluff body problems. The self-similar wake velocity defect that is normally independent of the near field wake (and hence body geometry) is modified using a combined approximate Green's function/Gram-Charlier series approach to retain the body geometry information. Formally a near field velocity defect profile is created using small disturbance theory and the inviscid flow field associated with the body of interest. The defect solution is then used as an initial condition in the approximate Green's function solution. Finally, the Green's function solution is matched to the Gram-Charlier series yielding profiles that are integrated to yield the net form drag on the bluff body. Preliminary results indicate that drag estimates computed using this method are within approximately 15% as compared to published values for flows with large separation. This methodology may be of use as a supplement to CFD and experimental solutions in reducing the heavy computational and experimental burden of estimating drag coefficients for blunt body flows for preliminary design type studies. © 2004 by the American Institute of Aeronautics and Astronautics, Inc.

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Though not discussed extensively in the literature, it is known among workers in impact and penetration dynamics, e.g. the CTH analysis and development team at Sandia National Laboratories, that curvature of thin plates has a minimal effect on the penetration hole diameter due to a hypervelocity impact. To understand why curvature introduces a minimal effect on penetration hole size we extend a flat plate penetration hole diameter relationship (De Chant (2004a) Unpublished manuscript; De Chant (2004b) Mechanics of Materials, in press) to include the effect of body curvature. The effect of the body curvature on the hole diameter is shown to scale according to the dimensionless plate thickness to radius of curvature of the body i.e. h/R, which is typically small. Indeed for most problems where a single layer shell (plate) can be meaningfully defined, the effect of curvature upon hole diameter is on the order of other uncertainties in the problem, e.g. doubts concerning the appropriate equation of state and strength model, and is often, therefore, negligible. © 2004 Published by Elsevier Ltd.

At 70 miles per hour, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck vehicle. The goal of this US Department of Energy supported consortium is to establish a clear understanding of the drag producing flow phenomena. This is being accomplished through joint experiments and computations, leading to the smart design of drag reducing devices. This paper will describe our objective and approach, provide an overview of our efforts and accomplishments, and discuss our future direction.

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.