Jet pressure-spectra estimation from single-snapshot tomographic PIV

Abstract

The analysis of the unsteady flow field of an axisymmetric subsonic jet at Reynolds numbers between 5,000 and 20,000 and computation of its unsteady pressure field is carried out from single snapshots of tomographic PIV measurements (acquisition rate 0.8 Hz). This is achieved by a recently developed pressure-evaluation technique based upon the vortex-in-cell (VIC) methodology. The technique allows for a finite time-marching of the instantaneous 3D velocity fields obtained from low-repetition PIV systems. A time series of velocity fields in 3D is obtained, which is integrated into unsteady pressure by use of the Navier-Stokes momentum equation. Despite the limitations in the finite-time marching of the measured structures due to the size of the acquired tomographic volume, spectra of pressure fluctuations can be extracted in a frequency range between 800Hz and 20kHz. Fair agreement was found between the experimentally computed pressure spectra and the respective values found in literature. Further work is dedicated to exploit the full potential of the technique by attempting a sound pressure level integration of the noise sources from the unsteady fields.