Abstract
Heated transitional supersonic jets exhausting from a rectangular nozzle at over-expanded conditions are investigated by Large Eddy Simulations and Ffowcs-Williams and Hawkings acoustic analogy. Four cases with a fixed nozzle pressure ratio but different temperature ratios (TR) of 1.0, 2.0, 4.0, and 7.0 are analyzed. Numerical results show that with the increasing temperature the jet velocity significantly increases, whereas its Reynolds number decreases by about one order of magnitude, which leads to a 30% decrease in the jet potential core length and reduction in the number of shock cells. The increasing temperatures also result in supersonic shear layer convection Mach numbers and consequently Mach wave radiations in the acoustic fields. Pressure skewness and kurtosis factors indicate crackle noise and non-linear propagation effects in high temperatures. For the most heated jet TR 7.0, the Mach wave radiation is identified radiating noise at about 120 degrees, while the large turbulence structure noise at about 150 degrees. Furthermore, the vortex sheet model analysis and the LES data detect the existence of upstream-propagating neutral waves inside jet TR 7.0. The observed screech frequency falls within the range of antisymmetric mode indicating that the highly-heated jet is characterized by an antisymmetric oscillation mode at the screech frequency.
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