Direct Numerical Simulation of Turbulent Flow Over Dimples – Code Optimization for NEC SX-8 plus Flow Results

The objective of the project DIMPLE is to study complex turbulent flows over a dimpled surface which is expected to lead to drag reduction compared to a smooth surface. In order to understand the physical mechanism of the flow over an arrangement of shallow dimples, CPU time-consuming direct numerical simulations were carried out using two different grid resolutions and three different configurations. As a first step within this project, the code LESOCC was evaluated and optimized for the new vector machine NEC SX-8. Classical vector systems still combine excellent performance with a well-established optimization approach. On the other hand, clusters based on commodity microprocessors offer comparable peak performance at much lower costs. In the context of the introduction of the NEC SX-8 vector computer series we compare single and parallel performance of a computational fluid dynamics application on the SX-8 and on the SGI Altix architecture demonstrating the potential of the SX-8 for teraflop computing in the area of turbulence research and flow control. Finally, results of the flow predictions over a dimpled surface are presented and compared with the reference case of plane channel flow with smooth walls.