Experimental Investigation into the Turbulence Flowfield of In-Flight Round Jets

Abstract

In this paper, insight is provided into the modeling of single-point and two-point statistics of a subsonic round jet discharged into a moving ambient medium. An experimental campaign has been performed comprising two round, unheated air flows: a central jet at Mach number equal to 0.6 surrounded by a slower flight flow. Constant-temperature hot-wire anemometry was used to measure both the axial and radial velocity fluctuations within the turbulent jet flowfield. A Mach 0.6 jet was discharged into the flight flow, which ranged from zero up to Mach 0.3. The data show that the degree to which the jet stretches with increasing flight velocity can be discerned with the knowledge of the decay of the mean velocity field downstream of the end of the jet’s potential core. This stretching factor can then be used to predict the changes in the static jet turbulence statistics for the in-flight case. Additionally, in the region of high-turbulence kinetic energy, the two-point statistics can be estimated using information about the single-point statistics and the local mean velocity. Empirical models for the in-flight jet’s shear stresses, cross-correlations, and power spectral density functions are presented and compared with those derived for the static jet case.