Compressibility Effects in Turbulent Subsonic Jets

Abstract

The behavior of compressible turbulent jets issuing in still air in the absence of shock waves has been investigated at three different subsonic Mach numbers, 0.3, 0.6 and 0.9. Helium, nitrogen and krypton gases were used to generate the jet flows and investigate the density effects on the structure of turbulence. Particle Image Velocimetry and high-frequency response pressure transducers were used to obtain velocity, Mach number inside the flow field. The decay of the Mach number at the centerline of the axisymmetric jets increases with increasing the initial Mach number at the exit of the flow for all jets. The decay of mean velocity at the centerline of the jets is also higher at higher exit Mach numbers. However, the velocity non-dimensionalized by the exit velocity seems to decrease faster at low exit Mach numbers suggesting a reduced mixing with increasing the exit flow Mach numbers. Helium jets were found to have the largest spreading rate among the three different gas jets used in the present investigation, while krypton had the lowest spreading rate. Total pressure fluctuations appear to decrease with increasing exit flow Mach numbers. Unusually high turbulence intensities were measured in helium jets issuing in still air.