Flow field characteristic of high Reynolds impinging zero-net-mass-flux jets

The purpose of this research is to experimentally study the influence of the Strouhal number (0.044, 0.022 and 0.011) and the orifice-to-plate distance (2, 4 and 6 orifice diameters) on the flow field of an impinging zero-net-mass-flux (ZNMF) jet at high Reynolds number (35000) by using PIV technique. These jets are generated by a reciprocating piston which oscillates in a cavity behind a circular orifice. Instantaneous two-dimensional in-plane velocity fields are measured in a plane containing the orifice axis by using cross-correlation digital particle image velocimetry. The behavior of the impinging ZNMF jets varying the Strouhal number and the orifice-to-plate distance is analyzed and discussed. The features of the mean flow quantities and its turbulent statistics have been described. A different axial velocity profile approaching the impinging plates is observed as the orifice-to-plate distance increases. At high orifice-to-plate distance a bell-shape profile is visible while, at lower distance, a minimum on the jet axis is observed. The Strouhal number influences the jet centerline velocity and the jet width. As the Strouhal number increases the jet centerline velocity decreases and the jet shows a greater spreading rate. A region of low turbulence has been detected, and the extension of such a region is influenced by the Strouhal number.