Effect of Upstream Geometry on Broadband Shock Associated Noise and Screech Tones in Trapezoidal Nozzles

The goal of this paper is to finalize a preliminary design for a nozzle of trapezoidal cross- section. The effect of upstream geometry on the noise produced from the supersonic jets will be investigated. Two nozzles, each with trapezoidal base angles of 75 degrees and height of 0.8 in were tested. Each nozzle shifts its cross-section from circular to trapezoidal in the converging section, one of which begins its convergence immediately (LongCD nozzle), while the other maintains its inlet cross-section for 1.76 in before converging (ShortCD nozzle). The ShortCD nozzle performs drastically better, with the LongCD nozzle suffering from high levels of broadband shock associated noise and screech tones throughout the range of NPRs tested. This results in the ShortCD nozzle tentatively being chosen as the baseline nozzle for later studies on downstream geometry effects.