CFD Simulation of Helicopter Downwash

Abstract

Several 3D CFD simulations of helicopter downwash are conducted in this master’s thesis. It aims to analyse the induced downwash pattern from a Search and Rescue (SAR) QUEEN helicopter, with and without the fuselage, on its surroundings and determine the mean downwash velocities while hovering at 50 feet and 90 feet and during landing at the Stavanger University Hospital (SUS).

Two case studies are conducted using the rotorDiskSource method and the overset mesh method for simulating helicopter downwash of the SAR QUEEN helicopter. The steady Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ω Shear Stress Transport (SST) turbulence model are used to simulate the turbulent helicopter downwash. A validation analysis of the CFD results with experimental data obtained from the Norwegian All-Weather Search and Rescue Helicopters (NAWSARH) project is completed to validate the rotorDiskSource method for predicting mean downwash velocities.

The CFD results from the hover simulations indicate that the peak mean downwash velocities are located at the periphery of the impact area, between the ground and the induced downwash. The highest mean downwash velocity is located 10 meters to the left of the downwash centre and 15 meters to the right of the downwash centre. The peak downwash velocity reaches up to 25 m/s. During the landing of the SAR QUEEN helicopter on the helipad at SUS, the mean downwash velocity at the cycle path behind the helipad and the garage underneath the helipad were assessed. The CFD results predicts a peak velocity of 8.2 m/s at the cycle path and 7.4 m/s at the garage.

The results from the validation analysis between the CFD results and experimental data show that the CFD results overestimates the mean downwash velocities. A sensitivity analysis was conducted to determine whether the mesh size influenced the accuracy of the results. The sensitivity analysis concluded that the CFD model resembles the experimental model as the mesh size increased. The generated CFD model of the SAR QUEEN helicopter functions as a conservative model to predict mean downwash velocities to determine pedestrian discomfort.