Design of a Dynamic Stall Test Rig

Abstract

Dynamic stall is an aerodynamic phenomenon that may occur when an airfoil is subjected to rapid, cyclical changes in angle of attack with respect to the incident ambient flow. This phenomenon can often produce repeated and significant changes in lift and moment coefficients within very short time frames, which manifest as severe and rapid changes in structural loads. Rotorcraft such as helicopters and wind turbines are particularly susceptible to dynamic stall, which is a highly undesirable operating condition. The condition plays a part in limiting the forward speed of a helicopter whilst also producing cyclical loads that accelerate fatigue. The structural issues are more severe for wind turbines, where blade spans approaching seventy to eighty metres are becoming common. Research into techniques for reducing the severity of the undesirable effects of dynamic stall is often conducting in laboratory environments using wind tunnels as the main investigative tool. The required cyclical changes in angle of attack are achieved by using machines that oscillate the test airfoil about an axis parallel to the span of the wing. Such mechanisms can be powered electrically, mechanically, pneumatically or hydraulically, and have various combinations of complexity, advantages and disadvantages. The current work describes the design process of an electrically powered dynamical stall test rig. The use of CAD / CAM to assist in the performing of design calculations and a comparison of the rig with other mechanisms is presented.