On the Application of Shock-Associated Noise Models to PIV Measurements of Screeching Axisymmetric Cold Jets

Imperfectly expanded jets have a quasi-periodic shock cell structure that interacts with the turbulent flow to generate broadband shock associated noise (BBSAN). Morris and Miller developed an acoustic analogyBBSANmodel that considers only the classic mixing noise scales that are based on the mean dissipation of turbulent kinetic energy. A recently proposed mixedscale model has been shown to improve noise predictions over a wider range of frequencies by coupling the mixing noise scale with the mean flow axial velocity gradient. The current work explores the dependence of the prediction schemes on the mean flow axial velocity gradient by comparing the correlation scales extracted from spatially-resolved 2D-2C particle image velocimetry (PIV) measurements. Measurements of screeching axisymmetric cold jets issuing from a purely converging nozzle at ideally expanded Mach numbers of 1:45 and 1:59 are considered. The PIV measurements are used to validate RANS solutions that simulate jets at comparable conditions. A k - ω SST turbulence model is used to yield the mean turbulence properties required to characterise the correlation scales. The correlation length scales are shown to depend strongly on the mean flow axial velocity gradient. A potential pathway for extending the BBSAN acoustic analogy prediction scheme to spatially resolved PIV measurements is explored by considering axisymmetric assumptions, which enable the approximating of the mean turbulent kinetic energy and dissipation rate.