Aerodynamic Noise Generated by Jet-Wing/Flap Interactions of the External USB Configuration of STOL Aircraft [I]8%-Scale Cold-Flow Model Analysis

The acoustic characteristics of the external upper surface blowing(USB) concept of a powered high lift system(PHLS) were studied experimentally using an 8% scale static cold flow model. Observations of exhaust jet flow attachment and spreading characteristics on wing/flap surface were also carried out using several flow visualization techniques. Noise reduction data were obtained by optimizing basic jet nozzle-wing/flap structural geometries for the lowest noise. Among the associated parameters which define USB-PHLS configurations, (I)the location relative to wing/flap and the shape of the exhaust jet nozzle and (II) flow attachment devices are important parameters. Flow characteristics dependence on these parameters and PHLS noise were also obtained. From far-field noise spectra, OASPL dependence on jet velocity and coherence across near field surface pressure, it was concluded that the flap trailing edge noise was the most predominant noise source. Several acoustically treated flaps and serrated trailing edge design techniques were applied to attenuate edge noise.