Suppression of Open-Jet Pressure Fluctuations in the Hyundai Aeroacoustic Wind Tunnel

Peak pressure fluctuation amplitudes in the ¾ open-jet test-section of the Hyundai Aeroacoustic Wind Tunnel have been reduced from root-mean-square levels equal to 6% of the test-section dynamic pressure to levels of less than 0.5% over almost the full wind speed range of the tunnel. The improvement was accomplished using a retrofit of the test-section collector. Using an analysis of the physics of the problem, it was found that the HAWT pressure fluctuations could be accurately modeled as a resonance phenomenon in which acoustic modes of the full wind tunnel circuit are excited by a nozzle-to-collector edgetone-feedback loop. Scaling relations developed from the theory were used to design an experiment in 1/7^th scale of the HAWT circuit, which resulted in the development of the new collector design. Data that illustrate the benefit of the reduction in pressure fluctuation amplitudes on passenger-car aerodynamic force measurements are presented.