Unsteady aerodynamic wake of helicopter main-rotor-hub assembly

Abstract

The helicopter tail shake phenomenon is an area of great concern to helicopter manufacturers as it adversely affects the overall performance and handling qualities of the helicopter, and the comfort of its occupants. This study is intended to improve the understanding of the unsteady aerodynamic load characteristics triggered by the helicopter main-rotor-hub assembly wake that lead to this phenomenon by experimental and numerical investigations. In this research work, a simplified NASA standard fuselage model was mated to a main-rotor-hub assembly from a remote-control helicopter. Data of pressures and velocities inside the wake, as well as the aerodynamic drag, corresponding to the variations of helicopter’s advance ratios and pylon configurations were captured. This work had gained some useful information towards further understanding of this long running issue, with a potential to minimise the problem. The dynamic analysis, through the power spectral density, root-mean-square and probability density function analyses, was also conducted and had successfully quantified the frequency and unsteadiness of mainrotor- hub assembly wake. Computational Fluid Dynamics (CFD) had also been carried out to model and simulate the wake dynamics, and were successfully validated using experimental results. The Sliding Mesh method was opted to simulate the rotation of main-rotor-hub assembly whilst the aerodynamic flow field was computed using the Large Eddy Simulation equations. As the CFD results were found to be in accordance with the experimental results, a reliable CFD modelling technique for the unsteady wake analysis of the helicopter main-rotor-hub assembly wake has thus been forwarded. Accordingly, this numerical modelling could be used to supplement experimental work. In addition, this research programme had also successfully proposed a modelling technique of simplified helicopter main-rotor-hub assembly viable for unsteady aerodynamic wake studies.