High-Temperature Effects on Aerodynamic and Acoustics Characteristics of a Rectangular Supersonic Jet

Implicit large-eddy simulations (LES) are performed in this work to study the flow field and acoustic characteristics of a rectangular supersonic jet. The focus is to investigate the high-temperature effects, i.e. when the jet total temperature is as high as 2100 K. Four cases with a jet temperature ratio(TR) of 1.0, 2.0, 4.0 and 7.0 are investigated. The rectangular nozzle selected for this study has an aspect ratio of 2. The jets are overexpanded, with a series of shock cells in the jet core region. An artificial dissipation mechanism is used to damp the numerical oscillation and to represent the effect of small-scale turbulence. The temperature-dependent thermal properties of air within the high-temperature regime are also considered by using the chemical equilibrium assumption. The numerical results show that the high temperature significantly increases the jet velocity and acoustic Mach number, although the jet Mach number is maintained roughly the same. Meanwhile, the length of the jet core region of the hot jet (TR = 7.0) is found to be reduced by around 30 %, compared to the cold jet. The convection velocity and acoustic convection Mach number in the shear layer are also observed to be increased when the jet temperature is high. The elevated acoustic convection Mach number directly leads to a strong Mach wave radiation, and the crackle noise component has been identified by the pressure skewness and kurtosis factors. The Strouhal number of the screech tone is found to be decreased slightly, and good agreements between the numerical results and the theoretical analysis are observed. Moreover, the sound pressure levels (SPL) associated with turbulent mixing, screech, Mach wave radiation, and Broadband shock associated noise are all found to be amplified in different levels for the hot jets. In the far field, the SPL are strongly affected and increased by the high-temperature effect. Higher levels are notably observed in the side, downstream, and especially the Mach wave radiation directions