Experimental Investigations of Transfer Phenomena in a Confined Plane Turbulent Impinging Water Jet

Abstract

In this study, we are interested in the hydrodynamics of impinging plane jets. Plane jets are widely used in ambience separation in HVAC, fire safety, food process engineering, cooling of electronic components etc. Despite their important industrial applications, plane jets have not been studied as extensively as axisymmetric jets. Plane jets exhibit different kind of instabilities stemming from either streamlines with strong curvature in the impingement region or inflection points in the transverse profile of the streamwise component velocity in the lateral mixing layers. Previous works in the GEPEA laboratory were performed on these flows. These works and the majority of the studies reported in the literature deal with turbulent air jets in various configurations. Very little studies have been done on water impinging jets. Taking into account the fact that the viscosity of water is smaller than air, at the same Reynolds number, it is easier to detect phenomena such as vortices. Phenomena can be observed at lower velocities making it possible to record signals with standard frequency bandwidths. This makes it easier also to do a Lagrangian tracking of vortices. We specially focused our study on the impinging zone of the jet. The dynamics of the impinging zone has not formed the subject of numerous studies. There were no studies that characterize the vortices at the impinging region of water jets in terms of size, centre position, vortex intensity, convection velocities, eccentricity, statistical distribution and turbulent length and time scales. Consequently, a confined water plane jet impinging a flat plate was studied using standard and high speed PIV (Particle Image Velocimetry). We used POD decomposition for filtering PIV data. Then, we applied the λ2 criterion to the recorded velocity fields to detect and characterize the vortices at the impingement. A statistical analysis was then performed. Turbulent length scales, time scales and convection velocities of eddies occurring at the impingement were determined using two point space time correlations. The obtained results were correlated to the dynamics and geometric properties of the jet. A wide range of Reynolds numbers is considered: 3000, 6000, 11000 and 16000. The corresponding results are presented in this paper.