Application of deflected leading and trailing edges to pitching airfoils and cycloidal rotor

Abstract

The cycloidal rotors are often applied to the energy propulsion equipment, and have been attracting more attention recently. The present work investigates the influence of both deflected leading (DLE) and trailing edges (DTE) on performance and flow structures over pitching airfoils and cycloidal rotors. The results show that the performance of a stationary hydrofoil, pitching airfoil and cycloidal rotor are improved evidently by morphing LE and TE simultaneously. It is very interesting that DLE of 5° with DLE of 20° can maximize the lift of oscillating airfoils and cycloidal rotors. However, although the side and propulsive forces of cycloidal rotor increase, the propulsive-force-based efficiency decreases with advance coefficient λ, because of the large power consumption. By using different combinations of DLE and DTE, the boundary layer transition, internal vortical flow, near-wall flow structure and wake flow exhibit much difference, and have close relationship with the performance change. For the cycloidal rotor, the blade with DLE and DTE can broaden the region of force production, but narrow the power extraction area. Changing λ can shift the stagnation point location, further affecting the near-wall flow and performance of the single blade. Increasing DLE makes the flow path longer, leading to an earlier occurrence of flow separation on one side of the blade, which is contrary on the other side. The change of DTE modifies the pressure gradient significantly, causing the variation of flow morphology and performance.