A wind tunnel experimental investigation for the flow normal to a flat plate attached with a closed membrane coating

Abstract

Wind tunnel experiments were conducted to study the flow normal to a flat plate attached with a closed flexible membrane. Two control parameters, the membrane width and the wind speed, were considered. A suspension device was designed to measure the aerodynamic forces exerted on the plate+membrane system. Experimental results show that, contingent on the membrane width, a significant drag reduction up to 22.2% is reported. Based on image recognition techniques, a measurement method using two high-speed cameras was developed to reconstruct the membrane’s motion. The time-averaged shape of the membrane is maintained as a plump D-shape cylinder. The membrane exhibits a rigid-body flapping motion and a bending deformation, accompanied by traveling waves along the membrane. Results of amplitude and standard deviation of the membrane motion show that the more intense flapping occurs on two sides of the membrane, while gentler flapping in the middle region. Furthermore, smoke-wire flow visualization reveals that the presence of the membrane significantly alters the flow structures in the delay in flow separation and the emergence of narrower wake structures, thus reducing drag. Our study demonstrates that such a flow control device using a flexible membrane coating is effective under 3D, high $Re$ and turbulent flow conditions, which providing powerful evidence of its potential for practical engineering applications.