Identification of Regions of Ship Airwake Influence on Helicopter Downwash Using Statistically Designed Experiments

摘要

A research program to investigate helicopter downwash/frigate airwake interaction has been initiated using a statistically robust experimental program featuring Design of Experiments. Engineering analysis of the helicopter/frigate interface is complicated by the fact that two flowfields become inherently coupled as separation distance decreases. The work presented was performed in the Old Dominion University Low Speed Wind Tunnel using a simplified 1/50 scale frigate waterline model and traverse mounted powered rotor with thrust measurement. Initially, PIV surveys of the frigate model landing deck in isolation and the rotor in isolation were performed to provide a baseline flow understanding. Next a designed experiment was devised yielding a response model for thrust coefficient as a function of vertical and longitudinal distance from the hangar door (base of the step), both with and without the rotor. This first experiment showed that thrust coefficient could be measured with enough precision to identify changes due to location using an advance ratio of 0.075 (V_∞=16.86 ft/s and ω=5000 rpm). A second designed experiment determined the practical spatial resolution for mapping the thrust coefficient response along the frigate's longitudinal center plane. Finally, a third designed experiment directly compared rotor thrust measurements between airwake and no-airwake cases and successfully identified regions that differed with statistical significance. The results presented for this fundamental research demonstrate the feasibility of using a statistically robust comparison experiment to analyze the changes in rotor thrust due to helicopter downwash/frigate airwake interaction.