Numerical studies on unsteady helicopter main-rotor-hub assembly wake

Abstract

The objective of this research is to quantify viscous unsteady flow phenomenon observed behind a helicopter main-rotor-hub assembly, as the part is believed to be a major contributor to tail shake phenomenon. In this numerical investigation, the aerodynamic flow field was computed using Large Eddy Simulation equations. To simulate the wake dynamics, Multiple Reference Frames (MRF) method was applied to rotate the main-rotor-hub assembly. Simulations were also run with fairing installed on the main-rotor-hub assembly. The results concluded that fairing does significantly alter the wake's structures and help to reduce aerodynamic drag to about 5% lesser. In addition, analysis from power spectral density (PSD) had successfully quantified the frequencies of this unsteady wake, as well the strength of their amplitudes. It had also manifested a significant growth of wake amplitude to 109% when the rotor rotation was increased from 1400 rpm to 1600 rpm, implying a strong correlation between the flow unsteadiness and the speed of rotor rotation. These findings are alleged to be valuable for future research and development in the rotorcraft industry.