Leading Edge Flaps at Low Reynolds Numbers

Abstract

Leading edge flaps modeled after those observed on bird wings can improve lift at low Reynolds numbers and high angles of attack. Force measurements and flow visualizations were performed at Reynolds numbers from 4.0× 10 to 1.2× 10 with leading edge flaps, leading edge wires, and several conventional transition trips installed on an Eppler E423 airfoil. Surface-mounted turbulators were found to increase lift at low angles of attack but were ineffective at high angles of attack. The leading edge devices were effective only at high angles of attack, characterized by a sudden increase in lift at some critical incidence. Steeper flap deployment angles cause the increase in lift to be delayed to higher angles of attack. The findings support previous suggestions that the leading edge flap operates as a transition device.