Computational Study of Flow in the Underbody Diffuser for a Simplified Car Model

In this paper, using the facilities offered by the ANSYS CFX, CFD code, the authors investigate numerically the flow around the Ahmed body for the rear slanted upper surface of 35°, fitted with a simple underbody diffuser, without endplates, in order to find the influence of the later one on the main aerodynamic characteristics, drag and lift. Relative motion between body and ground is simulated. The study is performed for different geometrical configurations, length and the angle of the diffuser being the parameters which are varied in ranges which are relevant for hatchback passenger cars. Later, based on a theoretical approach, a coefficient of the equivalent hydraulic resistance of the diffuser is computed, which helps to evaluate the drag due to underbody diffuser.