Inter-Rotor Spacing Effects On Interactional Aerodynamics And Acoustics Of A Coaxial Compound Helicopter In Forward Flight

Abstract

The coaxial rotor is utilized in a high-speed and long-range compound helicopter as its main rotor system, eliminating the need for a tail rotor. To enhance the compound helicopter's survivability, the coaxial rotor system must be designed aerodynamically efficient with low noise. The value of inter-rotor spacing (IRS), which refers to the distance between the upper and lower rotors, is a critical design parameter that determines a coaxial rotor system's aerodynamic and noise performance. This study conducted the computational investigation of the effects of IRS on the interactional aerodynamics and acoustics of the coaxial rotor in low and high-speed forward flight conditions using Spalart-Allmaras detached eddy simulation (SA DES) with the over-set mesh technique. When IRS increases, the growth rate of thrust is analyzed to be higher in low-speed conditions than in high-speed conditions, and the fluctuation's amplitude decreases more. Regarding noise, in both conditions, as IRS increases, the impact of loading noise decreases, resulting in a reduction in noise levels.