Research on the Separation Control Characteristics of Vortex Flap under Different Reynolds Numbers

Abstract

Inspired by birds raising their feathers to control the separation flow, vortex flap has become an approach to control the separation flow over airfoils at high angles of attack.In this paper, the aerodynamic characteristics and physical mechanism of vortex flap controlling separation flow over airfoils under different Reynolds number are numerically studied.The results show that vortex flap is able to greatly improve the lift of airfoil at low Reynolds number under high angle of attack.Its physical mechanism is that the vortex flap makes the core position of main separation vortex closer to the airfoil comparing to the original airfoil, and the vorticity of the vortex center position is also greatly improved so that the low-pressure characteristics caused by the vortex core will affect the flow field on the upper airfoil surface.In addition, the pressure filed on the upper surface of the airfoil is divided by vortex flap into two parts:the low pressure aera in the front and the high pressure aera at the back.However, under high Reynolds number(corresponding to conventional aircraft Reynolds number), the effect of vortex flap on improving the aerodynamic characteristics of airfoil at high angle of attack is far less effective compared to the case of low Reynolds number.This explains why birds can improve lift characteristics through feather lifting, while vortex flap can only be used as drag plates in conventional aircraft.

Keywords

• flow control
• reynolds number
• vortex flap
• high angle of attack
• numerical simulation