PASSIVE CONTROL OF FLOW IN AN A-PILLAR REGION IN THE PRESENCE OF UNIFORM OR TURBULENT UPSTREAM FLOW

The flow at the level of A-pillar region is characterized by complex and unsteady three-dimensional separated areas. They are mainly responsible for pressure fluctuations which are the source aerodynamic noises radiated outward or transmitted in the passenger compartment. This noise can make the driver tired and stress the passengers in the cabin. Therefore, one of the technological challenges for ground vehicles is the reduction of noise generated by these aerodynamic sources. At the present time, active control devices are wanted to control the vortex and its interaction with the wall (lateral windows). However, fixed devices can also be installed to a form of passive control which will play on the relative position of the vortex and its dynamics. In the present work, simple geometric devices were installed on the A-pillar strut of a model body to modify the development of the conical vortex and its fluctuating pressure footprint. Two strategies were tested. The first consisted in a narrow plate running along the A-pillar, expected to modify the A-pillar strength and its position relative to the side wall. The second consisted in generating a secondary vortex, intense enough to interact with the main structure. The efficiency of these devices has been tested in the presence of a uniform upstream flow and a turbulent upstream flow. The isotropic and homogeneous turbulent flow was generated using a grid placed in the entry of test section, generating an intensity of 4% and an integral length scale of the magnitude of the A-pillar vortex diameter. For a uniform upstream flow, it was observed that the simple geometric devices used made the vortex core more energetic and coherent. Moreover, the group of devices acting as a vortex generator was able to very significantly reduce the coefficient of fluctuating pressure. Such an improvement was however not obtained in the presence of upstream turbulence.