Application of High Fidelity Numerical Simulations for Vehicle Aerodynamics

Abstract

Interest in the use of the large eddy simulation (LES) technique for computation of turbulent flows of industrial relevance has increased considerably. This is in part due to the availability of low cost, powerful supercomputers. Today, a computer cluster capable of one TFOPS sustained performance for a complex flow LES calculation costs about one hundred thousand dollars. Another reason for the increased interest in LES is the recent added capabilities for multi-physics and integrated flow simulations. As part of Stanford’s DOE/ASC program, we have demonstrated and validated high fidelity simulations of multi-phase reacting turbulent flows in highly complex configurations in propulsion systems. The overarching problem in this program is simulation of flow through a complete jet engine, which is an extremely complex machine. LES computations of the entire engine flow are not feasible even with the most advanced supercomputers available. The Reynolds averaged Navier-Stokes (RANS) technique was used for the turbomachinery components and the combustor was simulated using LES. These simulations provided an early example of integrated simulations where different codes with different fidelity compute different portions of the system. A simulation environment had to be developed for the various codes to communicate with each other in an efficient and stable fashion. This integration technology and the associated science are suggested as the means for using LES in vehicle aerodynamics where Reynolds numbers are too high for high fidelity computation of the flow around the entire vehicle. LES can then be used in regions where RANS models are known to be inaccurate, and where LES provides access to flow quantities such as turbulent pressure fluctuations for predicting noise. Several examples of integrated simulations will be presented, including separation control for a high-lift system using synthetic jets.