Identification and Analysis of Turbulent Structures Around a Simplified Car Body

摘要

The analysis of turbulent flow around road vehicles can be very complex. Each geometrical detail releases turbulent structures; they interact each other and with those inside the car main wake. In bluff bodies, aerodynamic wake analysis is a basic step and an effective method to identify Coherent Structures (CS) making wake structure understanding easier. In this work the flow field around a simplified car model, the Ahmed Body, has been investigated to identify turbulent structures and to analyse their influence on vehicle drag. Three different geometrical configurations with 0°, 25° and 35° slant angles have been investigated by means of Reynolds Averaged Navier-Stokes equations (RANS). The Reynolds number has been set to 7.68 x 10~5, while the grid is structured and contains 3.5 x 10~6 cells. Two turbulence models, the k-ε and the Reynolds Stress Model (RSM), are also compared. CS visualization has been performed by the Jeong and Hussain method and it has been compared with the following common methodologies: static pressure minimum, vorticity magnitude, total pressure drop and second invariant of the velocity gradient. It will be shown that, among the visualization methods analysed, the one proposed by Jeong and Hussain seems to be the most efficient and effective