Fluctuating Pressure Gradients in Heated Supersonic Jets

Abstract

A combined experimental and computational study has been conducted to examine the behavior of fluctuation pressure gradients in heated supersonic jets. This quantity is closely related to the behavior of acoustic noise sources in the jets studied and also indicates some of the links between the hydrodynamic field in the jet and the hydrodynamic/acoustic near field immediately around the jet. Results from a model scale experiment revealed acceleration variance, which is directly linked to pressure gradient variance in the limits of high Reynolds number, that was similar in magnitude for both stream-wise and radial pressure gradients. Computations provided more detail that could be obtained from the experiments and reveal a field of rich dynamics in the pressure gradient variance fields. The results of both experiments and computations are largely consistent, although the computations exhibit more anisotropy of the variance in the stream-wise and radial gradients, particularly in the core of the jet. A key difference between experiments and computations occurs at the apparent origin of Mach wave radiation in the flow. Computations reveal an intense region of stream-wise pressure gradient variance that is not reflected in flow stream-wise acceleration variance along the lip line. Close inspection reveals that this peak region lies closer to the axis than the lip line, likely explaining the difference. It is to note that the close relationship between the region identified in the computations with high stream-wise pressure gradient variance and the Mach wave radiation region may provide a method to correlate hydrodynamic flow features (stream-wise pressure gradient or acceleration fluctuations) to the radiated field in those directions.