Supersonic Jet Noise Reduction via Pulsed Microjet Injection

This paper compares the noise suppression abilities of steady and pulsed microjet injection for a Mach 1.8 jet operating at 900, 1300, and 1700°F. Pulsing was performed at 1, 5, and 10 Hz at duty cycles of 50 and 75%, and was compared with steady microjet injection. For pulsing at 50 % duty cycle, 33 to 57 % of the noise reduction of steady injection was achieved. For pulsing at 75 % duty cycle, 60 to 75 % of the noise reduction of steady injection was achieved. For injection at a given pressure, the noise reduction increases with duty cycle, where steady injection corresponds to a duty cycle of 100%. This paper shows that equivalent noise reduction can be achieved with pulsing using less water as compared to steady injection. At a given mass flow rate, noise reductions are comparable, if not better, when using pulsing as opposed to steady injection. I