Airframe Noise Study of a Bombardier CRJ-700 Aircraft Model in the NASA Ames 7-by 10-Foot Wind Tunnel

An acoustic and aerodynamic experimental study was conducted of a 7%-scale unpowered Bombardier CRJ-700 aircraft model in the NASA Ames 7- by 10-Foot Wind Tunnel for the purpose of identifying and attenuating airframe noise sources. Simulated landing, takeoff and approach configurations were evaluated at Mach 0.22 and 0.26. With a phased-microphone array mounted in the ceiling over the inverted model, various noise sources in the high-lift system, landing gear, fins, and other miscellaneous components were located and compared for sound level and frequency at one flyover location. Numerous model modifications and noise-alleviation devices were evaluated. Simultaneous with acoustic measurements, aerodynamic forces were recorded to document aircraft conditions and any performance changes caused by the geometric modifications. Such performance changes were small and are not reported here. Ten airframe noise sources were identified that might be important to approach and landing noise of the full-scale aircraft The top five noise sources were: a) slat gap, b) main gear, c) flap tips at wing crank, d) flap inboard gap, and e) slat inboard tip. Relative strengths of these sources were documented along with their dependence on aircraft configuration and operating condition. Although the data were scaled to full-scale frequencies, no extrapolation to full-scale flyover was attempted.