Numerical Simulations and Measurements of the Wake from a Helicopter Operating in Ground Effect

Helicopter downwash interferes with the ground when a helicopter takes off or lands, or makes hovering / taxiing flights in ground effect. By encountering this highly turbulent helicopter wake, two small fixed-wing aircrafts was rolled over in the United Kingdom. Driven by these accidents, Japan Aerospace Exploration Agency (JAXA) is investigating the helicopter wake structure in ground effect, especially in taxiing by CFD and flight test. The base CFD code is a structured grid solver, <rFlow3D>, which has systematically been developed for helicopter applications at JAXA. The rFlow3D is a highly versatile CFD code that can numerically simulate flows around helicopter in a wide range of Reynolds and Mach numbers, including rotor trim analysis with elastic blade deformations. On the other hand, in the flight experiment, JAXA's research helicopter H145 (EC145, BK117 C-2) conduct taxiing above a runway and its wakes are measured by LIDARs and ultrasonic anemometers. The characteristic wake structure variations with advance ratio are clearly shown in CFD and are supported by the flight experiment results indirectly.