Control of Reverse Flow on High-Speed Rotorcraft Using a Blade with a Sinusoidal Trailing Edge

Abstract

One of the main challenges limiting the maximum forward speed of high-speed rotorcraft is the development of reverse flow on retreating blades. Flow separation at the sharp aerodynamic leading edge during reverse flow leads to negative lift, high drag, high pitching moment, and a pitching moment impulse. The study experimentally investigates the effectiveness of a sinusoidal trailing edge as a passive method for the control of reverse flow, under static pitching conditions. Three NACA 0015 two-dimensional blades were evaluated under both reverse and forward flow conditions. A baseline blade with a straight trailing edge and two modified blades with sinusoidal trailing edges, each having a spatial amplitude of 10% of the chord and wavelengths of 5% and 10% of the chord, respectively. Experiments were conducted at chord-based Reynolds numbers of 70000 and 140000, consisting of planar Particle Image Velocimetry and aerodynamic load measurements. The study shows that a sinusoidal trailing edge significantly mitigates flow separation, leading to a large reduction in the associated problems over a wide range of angles of attack. The problem of pitching moment impulse is eliminated. The sinusoidal geometry with a lower wavelength of 5% of the chord shows comparatively better performance. Additionally, both sinusoidal geometries minimally affect the forward flow characteristics.