École Nationale Supérieure de
Techniques Avancées

Résumé

This report investigates the effect of geometrical variations on the static wake instability of bluff bodies. The model used is an Ahmed body with a rectangular section, whose base ratio select the horizontal bi-stability of the wake. The angles of the flat rear can be changed, as well do the front shape and the yaw inclination of the model. Pressure measurements on the body are used to analyse the wake instability. This report shows the effect of angled rear, if the angle is around the major axis of the base, there is a threshold angle value (around $15\degree$) above which the dynamic changes : the wake rotates by $90\degree$ and is not bi-stable any more. This dynamics can be reversed using side perturbations. A back angle around the minor axis only shifts the bi-stable area and the pressure values. The effect of a front asymmetry also shifts the bi-stable area and modifies the pressure values.