Shock Cell Modification Due to Chevrons

Abstract

*† ‡ Tests were conducted to determine the effect of chevrons on the turbulence and shock cell strength of nozzles operated at under expanded conditions. Baseline (or conical) and chevron nozzles were tested on the core (primary) stream in a coaxial nozzle configuration that simulated a high bypass ratio engine exhaust. The secondary (fan) stream was varied from quiescent condition to Mach = 0.85 to simulate external flow. For all cycle points, turbulence in the region of the shock cells was higher for the chevron configuration than for the baseline configuration. For the three lower coflow Mach numbers (0, 0.28, and 0.50) the strength of the shock cells with the chevron nozzle were comparable in strength to those with the baseline nozzle. For the highest coflow (Mach 0.85), the strength of the shock cells with the chevron nozzle was significantly less than the strength of the shock cells with the baseline nozzle. These results explain acoustic trends from previous work 1 . For the three lower values of coflow, higher turbulence and comparable strength shock cells from the chevron configuration lead to higher shock noise compared to baseline configuration. Alternatively, at the highest coflow (Mach 0.85) slightly higher turbulence and significantly reduced strength shock cells for the chevron configuration lead to lower shock noise compared to the baseline configuration.