Reverse flow on the retreating side of a rotor disk is an intrinsic aerodynamic limitation of high-speed,high advance ratio rotorcraft.For traditional single main rotor helicopters,the influence of flow reversal is no...Reverse flow on the retreating side of a rotor disk is an intrinsic aerodynamic limitation of high-speed,high advance ratio rotorcraft.For traditional single main rotor helicopters,the influence of flow reversal is not significant,but it is important for coaxial rigid rotor high-speed helicopters.Flow reversal can be a source of several unsteady flow phenomena such as vortex formation,which increases the pitch link loads that could ultimately lead to fatal crashes.The aim of the current work is to reduce pitch link loads by using blunt trailing-edged blades.Experiments and numerical simulations were compared to a simple low-order model for a quick blade design iteration process.The focus of the present study is on blade aerodynamic loading,namely the blade vertical force,the horizontal force,and the blade pitching moment.A range of advance ratios and blade pitch angles were studied.A 29% pitching moment increase was measured in the reverse flow region with sharp trailing-edged blades compared to blunt blades.The blunt trailing-edged blade delayed flow separation and thus prevented the formation of a reverse flow dynamic stall vortex,reducing the pitching moment.The use of such blunt trailing-edged blades could save pitch links from failing and may ultimately help prevent rotorcraft from fatal crashes.展开更多
基金supported by the Office of Naval Research with David Gonzalez serving as Program Manager(grant number:N00014-21-S-B001).
文摘Reverse flow on the retreating side of a rotor disk is an intrinsic aerodynamic limitation of high-speed,high advance ratio rotorcraft.For traditional single main rotor helicopters,the influence of flow reversal is not significant,but it is important for coaxial rigid rotor high-speed helicopters.Flow reversal can be a source of several unsteady flow phenomena such as vortex formation,which increases the pitch link loads that could ultimately lead to fatal crashes.The aim of the current work is to reduce pitch link loads by using blunt trailing-edged blades.Experiments and numerical simulations were compared to a simple low-order model for a quick blade design iteration process.The focus of the present study is on blade aerodynamic loading,namely the blade vertical force,the horizontal force,and the blade pitching moment.A range of advance ratios and blade pitch angles were studied.A 29% pitching moment increase was measured in the reverse flow region with sharp trailing-edged blades compared to blunt blades.The blunt trailing-edged blade delayed flow separation and thus prevented the formation of a reverse flow dynamic stall vortex,reducing the pitching moment.The use of such blunt trailing-edged blades could save pitch links from failing and may ultimately help prevent rotorcraft from fatal crashes.
