On the linearity of the quieting of high speed mixing layers by heating

High-speed mixing layers are known become quieter when the high-speed stream is heated at constant velocity. The cause of the noise reduction is not known but it is hypothesized that it can be partially explained through modification of the mixing layer's large scale dynamics. It is found through simulations of the linearized dynamics that the large-scale entropy fluctuations play an increasing role with increased temperature, as expected, but also that these fluctuations are partially responsible for reducing the radiated sound. Preliminary results from a multiscale linear theory are developed toward explaining this observation and suggest that the entropy fluctuations are less efficient sound radiators.