TAFSM

Team for Advanced Flow Simulation and Modeling



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Airflow Past an Automobile

Airflow past an automobile (modeled after a Saturn SL2) at 55 miles per hour is simulated. The model is quite detailed and includes the wheels, recessed headlights, and a spoiler. This tetrahedral mesh contains 447,180 nodes and 2,801,488 elements. At each time step, a system of equations with 1,638,389 unknowns is solved using matrix-free iterations.

The incompressible flow, with a modified Smagorinsky turbulence model, was computed under two flow conditions. The first simulation modeled road conditions. Here, we applied the free stream velocity to both the inflow boundary and the road, and we forced the wheels to spin (a rotational flow field was imposed on the tires). Zero velocity was imposed on the rest of the automobile. This flow condition yielded a drag coefficient of 0.433.

The second simulation modeled wind tunnel conditions. Here, we applied the free stream velocity just at the inflow boundary, and applied slip conditions on the road. Zero velocity was imposed on both the tires and the automobile. This flow condition yielded a drag coefficient of 0.335. The actual drag coefficient of a Saturn SL2 automobile under wind tunnel conditions is 0.343.

Shown in the figures are the pressure distribution on the automobile and the road (red being high pressure and blue being low pressure), and the streamlines around the automobile (the streamline colors represent the magnitude of the velocity). The simulations of flow past the automobile was also partially carried out on the Cray T3D. The unstructured mesh generator, flow solver, and flow visualization software (based on Visual3 library and Wavefront) were developed by the T*AFSM.

The flow simulations for the automobile were part of an effort by the T*AFSM researchers, partially funded by the Advanced Research Projects Agency, for the development of scalable libraries for fluid mechanics applications.

      

References:

1. T.J.R. Hughes, T.E. Tezduyar and A.N. Brooks, "Streamline Upwind Formulations for Advection-Diffusion, Navier-Stokes, and First-order Hyperbolic Equations", Proceedings of the Fourth International Conference on Finite Element Methods in Fluid Flow, University of Tokyo Press, Tokyo (1982).

2. T.E. Tezduyar, "Stabilized Finite Element Formulations for Incompressible Flow Computations", Advances in Applied Mechanics, 28 (1991) 1-44.

3. T.E. Tezduyar, S. Mittal, S.E. Ray and R. Shih, "Incompressible Flow Computations with Stabilized Bilinear and Linear Equal-order-interpolation Velocity-Pressure Elements", Computer Methods in Applied Mechanics and Engineering, 95 (1992) 221-242.

4. T.E. Tezduyar, M. Behr and T.J.R. Hughes, "High Performance Finite Element Computation of Fluid Dynamics Problems", Computational Fluid Dynamics Review 1995 (eds. M. Hafez and K. Oshima), John Wiley & Sons (1995) 300-321.

5. A.A. Johnson and T.E. Tezduyar, "Parallel Computation of Incompressible Flows with Complex Geometries", International Journal for Numerical Methods in Fluids, 24 (1997) 1321-1340.

6. T. Tezduyar, "Advanced Flow Simulation and Modeling", Flow Simulation with the Finite Element Method (in Japanese), Springer-Verlag, Tokyo, Japan (1998).

7. T. Tezduyar, "CFD Methods for Three-Dimensional Computation of Complex Flow Problems", Journal of Wind Engineering and Industrial Aerodynamics, 81 (1999) 97-116.

8. T. Tezduyar and Y. Osawa, "Methods for Parallel Computation of Complex Flow Problems", Parallel Computing, 25 (1999) 2039-2066.