Numerical Simulations and Measurements of the Helicopter Wake in Ground Effect

Abstract

When a helicopter takes off, lands, or makes hovering or taxiing flights in ground effect, its downwash interferes with the ground. Encounters with such highly turbulent helicopter wakes have resulted in the two small fixed-wing aircraft crashes in the United Kingdom. Due to these accidents, the Japan Aerospace Exploration Agency is investigating the helicopter wake structure in ground effect, especially during taxiing, by means of computational fluid dynamics and flight testing. The base computational fluid dynamics code is structured grid solver rFlow3D, which has systematically been developed for helicopter applications at the Japan Aerospace Exploration Agency. The rFlow3D solver is a highly versatile computational fluid dynamics code that can numerically simulate flows around helicopters with a wide range of Reynolds and Mach numbers and can perform rotor trim analysis with elastic blade deformations. In the flight experiment described herein, the Japan Aerospace Exploration Agency research helicopter H145 (EC145, BK117 C-2) performed taxiing above a runway, and its wakes were measured by Light Detection and Ranging and ultrasonic anemometers. The variation of the characteristic wake structure with the advance ratio was clearly revealed in the computational fluid dynamics and was supported indirectly by the flight experiment results.