Numerical Investigation of Inter-Rotor Spacing Effects on Wake Dynamics of Coaxial Rotors

Abstract

In this Paper, the wake dynamics of coaxial rotors are studied using the high-wake-resolution method. The high-wake-resolution method is a novel combination of the truncated vortex tube model for initial and boundary conditions and the wave-number-extended finite-volume interpolation scheme. The wake resolution of this method is verified by comparison with other general computational fluid dynamics techniques. By using this method, this Paper analyses the wake dynamics of coaxial rotors with different inter-rotor spacing. The aerodynamic characteristics of coaxial rotors are compared with those of single-rotor systems to identify the effect of wake interaction on coaxial rotor blades. Variations of thrust and sectional thrust coefficients indicate that the lower rotor is continuously influenced by the wake of the upper rotor. In addition, the blade/vortex interaction and the wake instability phenomena are observed near the lower rotor. Aerodynamics and wake dynamics are strongly correlated with inter-rotor spacing. Details of important features such as the wake trajectory, miss distance of each rotor, blade-vortex interaction phenomenon, and wake instability at different inter-rotor spacing are discussed.