Wind tunnel investigation of dynamic stall of a NACA 0018 Airfoil oscillating in Pitch

Abstract

This report presents aerodynamic data on an NACA 0018 airfoil oscillating in pitch in the N AE 2m X 3m Low Speed Tunnel. The purpose of the test was to simulate the dynamic aerodynamic behaviour of a Vertical Axis Wind Turbine blade section at the equatorial plane under the dynamic stall conditions which may occur at low ratios of tip speed to wind speed. Measurements were made of wing surface pressure time histories at various chordwise locations, during a complete cycle of oscillation. The dynamic effects on nose suction pressures were seen to increase their magnitude and to delay flow breakdown to a higher angle of attack. Integration of wing pressures furnished normal and chordwise forces during the angle of attack cycle. The behaviour of these parameters showed that dynamic stall for wing angles of attack up to 30 degrees, occurred about 5 degrees later than for the equivalent steady flow case. This phenomenon resulted in an increase in normal force of about 20% and an increase in chordwise force of about 40% when the wing is pitching to 30 degrees.