Time-resolved stereo PIV measurements in the far-field of a turbulent zero-net-mass-flux jet

Abstract

This paper presents time-averaged and temporally evolving mean flow and turbulence statistics for a turbulent zero-net-mass-flux (ZNMF) jet at high Reynolds and Strouhal numbers in the far-field in a plane perpendicular to the jet axis. The measurements have been obtained using time-resolved stereo particle image velocimetry (TR-SPIV). The jet is generated by the oscillation of a piston, which discharges filtered water to the quiescent fluid in a tank through a round orifice. A multigrid cross correlation digital particle image velocimetry algorithm (MCCDPIV) has been used to compute the images from each camera that subsequently have been combined to obtain the three components of the velocity. Velocity and turbulence statistics are in good agreement with results obtained in previous work. A comparative study has been performed to determine the contribution to the spreading rate due to the displacement of the center of the jet as rigid body. Different criteria to define the instantaneous jet center have been considered. For the different cases carried out for this study it has been observed that subtracting the movement as a rigid body the width of the jet becomes similar to that of a continuous jet. Velocity fluctuation statistics are also influenced by this restriction. The image series have also been analyzed to determine the temporal evolution of the velocity field and its fluctuations. The fast Fourier transforms (FFT) have been used to calculate the power spectra of these variables.