Experimental investigation on effect of partial flexibility at low aspect ratio airfoil – Part I: Installation on suction surface

Wind Engineering and Aerodynamic Research Center, Department of Energy Systems Engineering, Erciyes University, Kayseri, TURKEY

^* Corresponding author: musgenc@erciyes.edu.tr

Published online: 24 October 2022

Abstract

Effects of flexible membrane mounted over suction surface of NACA 4412 airfoil were experimentally investigated at Reynolds number of 5x104 and low aspect ratio (AR=1) in this paper. The smoke-wire visualization method has been performed for flow visualization to demonstrate flow phenomena as laminar separation bubble (LSB), leading edge separation at z/c=0.4 and tip vortices at z/c=0.1. Values of velocity, Reynolds stress and turbulence statistics were measured by means of a constant temperature anemometer (CTA) system. Results of smoke-wire experiment revealed that size and height of LSB formed along z/c=0.4 at lower angles of attack such as α=8° was mitigated. Moreover, stall phenomenon as a result of boundary layer separation was apparently postponed at higher angles of attack. Velocity value was increased, whereas values of Reynold stress and turbulent kinetic energy was decreased with reduction of amount of fluctuations in flow. Consequently, using flexible membrane over suction surface of airfoil allowed the LSB to be mitigated or extinguished, resulting in exhibition of more stable flow characteristics.