Large eddy simulation of an Ahmed reference model

Abstract

This paper presents the first large eddy simulation (LES) of the Ahmed reference model. LES allows a much greater depth of analysis than most other turbulent simulation methods. Here the richness of information provided by LES is used to show a wide range of flow results such as: time averaged mean profiles, time-dependent traces, flow spectra and a number of two-dimensional and three-dimensional animations of the flowfield. The body geometry is analysed at a given slant angle of 28° using the PRICELES/TRIO_U code platform. This angle is chosen as it is close to the critical angle at which the flow changes between two different regimes. A non-structured tetrahedral grid is used which enables accurate modelling of the body geometry while avoiding the need for a prohibitively expensive mesh. The drag estimation and flow field visualizations indicate that the flow is in the regime corresponding to angles above the critical angle, although the geometry is just below the critical angle. The simulation revealed complex time dependence of the flow around the body. Visualizations of the Q criterion showed a series of horseshoe vortices being shed in the wake where previous studies indicated that the wake structure was made up of discrete contra-rotating vortices.