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Temperature Effects on Convection Speed and Steepened Waves of Temporally Developing Supersonic Jets

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Temperature effects on the convection speed of large-scale structures in supersonic temporally developing jets and on the steepened aspect of the acoustic waves generated by these structures are investigated. For that, one isothermal jet at Mach 2 and four others at static temperatures equal to two or four times that of the ambient medium are simulated at either the same exit velocity or Mach number as the isothermal jet. For all temporally developing jets, steepened acoustic waves are emitted in the near field, leading to significant values of the pressure skewness and kurtosis factors. Using conditional averages, their formation is directly linked to the supersonic motion of large-scale structures at a convection speed whose ratio with the jet velocity is shown to decrease with temperature. At a higher temperature, this leads to the generation of less skewed acoustic waves for a constant jet velocity. For a constant Mach number, however, this decrease is compensated by the rise of the jet speed, leading to steeper acoustic waves at a higher temperature. Therefore, the modification of the steepened aspect of near-field acoustic waves appears to be related to the change in the convection speed in both cases.