Unsteady aerodynamics over surface of a chambered airfoil at stall angle and low Reynolds number

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

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

Published online: 24 October 2022

Abstract

The proposal of this paper is clear to reveal and understand the unsteady flow characteristics over the surface of chambered airfoil operating especially at low Reynolds numbers by detecting boundary layer separation and laminar separation bubble (LSB). Experiments including smoke-wire technique for flow visualization, velocity measurement via hot-wire sensor and quasi-wall shear stress measurement by means of the hot-film sensor have been performed over the suction surface of NACA 4412 airfoil at Reynolds number of 5x104 and angle of attack of 14°. Experiments indicate that the airfoil at a stall angle exhibits the bistable characteristics over the suction surface because of the unsteady bubble bursting at low Reynolds numbers. That is, either laminar flow separates from the leading-edge of the airfoil owing to a dominant adverse pressure gradient (APG) or it does not separate along downstream. It is also noted that unsteady boundary layer formation may affect the flow characteristics by changing airfoil’s stability appreciably, causing the periodic fluctuations with the occurring bubble bursting and the leading edge and trailing edge vortex merging. This may conclude undesirable problems such as noise, vibration and flutter for the flight vehicles and wind turbines.