Aeroacoustic Characteristics of the Supersonic Free Jet at Mach Number 1.6

The goal of this research is to look at the aeroacoustic properties of optimum and non-optimum expansion characteristics of a Mach 1.6 free jet. The single jet of cold flow has been studied to better understand its aerodynamic and acoustic properties. To demonstrate the various expansion modes of the jet, the nozzle pressure ratios (NPRs) that were considered are 3.25, 4.25, and 5.25. The acoustic oscillations produced by these jets illustrate that the NPR has a substantial impact on the jet’s acoustic signature. The shock-cell behavior of the off-design operating jet was evaluated using the centerline Mach number decay and numerical shadowgraph methods. The overexpanded and underexpanded jets’ severe Mach number fluctuation virtually starts at X/De = 4; the variations travel downstream until the jets are fully expanded. The oscillation ends at X/De = 9 for the overexpanded jet, but at X/De = 13 for the underexpanded jet. The total shock-cell length of the underexpanded jet is 37% longer than the overexpanded free jet. The observed sound pressure level (SPL) for various microphone locations demonstrates the jet’s directivity. The SPL at 45° fluctuates significantly all across the frequency scale. The angles from 15° to 90° exhibit maximum SPL values between 125 and 170 dB. As the angle of the microphone increases from 15° to 90°, the maximum value of the SPL decreases. Also, the nature of variations of the SPL is virtually identical for the microphone locations of 30°, 60°, and 90°, whereas the remaining locations show a different trend along the frequency scale.