Abstract
The aerodynamic performance analysis and blade planform design of a coaxial rigid rotor in forward flight were carried out utilizing CFD solver CLORNS. Firstly, the forward flow field characteristics of the coaxial rotor were analyzed. Shock-induced separation occurs at the advancing side blade tip and severe reverse flow occurs at the retreating side blade root. Then, the influence of geometrical parameters of the coaxial rigid rotor on forward performance was investigated. Results show that swept-back tip could reduce the advancing side compressibility drag and elliptic shape of blade planform could optimize the airload distribution at high advance ratio flights. A kind of blade planform combining swept-back tapered tip and nonlinear chord distribution was optimized to improve the rotor efficiency for a given high-speed level flight based on geometric parameter studies. The optimized coaxial rotor increases lift-to-drag ratio by 30% under the design conditions.
Highlights
Coaxial rigid rotor helicopters with auxiliary propulsion are able to attain better performance at high forward speed compared with conventional single-rotor helicopters
The application of lift offset on coaxial rigid rotors plays an important role in the improvement of forward rotor efficiency
A coaxial rotor solver developed on CLORNS was applied to simulate the aerodynamics of the coaxial rotor in forward flight
Summary
Coaxial rigid rotor helicopters with auxiliary propulsion are able to attain better performance at high forward speed compared with conventional single-rotor helicopters. For the single-rotor configuration, the forward flight speed is restricted by dynamic stall on the retreating side and compressibility on the advancing side of the disk. Lift capability of advancing blades is limited to maintain lateral equilibrium. Lift offset concept of coaxial rotor offers a solution to the speed limitation problem. It allows the lateral asymmetry of the lift distribution. The advancing blades generate most lift of the disk, and the retreating blades are offloaded. Are limited analytical studies on coaxial rotor performance compared with single rotor configuration, as shown in the following.
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