Analysis of the effect of the 3C kinematic field of a confined impinging jet on a slotted plate by stereoscopic PIV

Abstract

Abstract Confined jets impinging on slotted surfaces are usually used in industry, transportation, housing and many other fields. In the construction industry, these jets can be used in ventilation systems to improve the mixing and diffusion of airflows. The terminal devices of these ventilation and air-conditioning systems can, in some cases, become sources of acoustic noise through the self-sustained tones that they can generate. Self-sustained tones occur when a feedback loop settles between the contact area of a jet with a slotted surface and the jet exit. In order to solve this problem, a detailed analysis of the jet must be carried out. The objective of this work was to analyse a flow by studying the effect of the third component of the kinematic field on large-scale structures and energy distribution. This study was performed by comparing the 2C and 3C kinematic fields measured by both PIV and SPIV acquisitions. First, an experimental platform was developed to generate a flow corresponding to the configuration of a confined impinging jet on a slotted plate. Secondly, time resolved particle image velocimetry (TR-PIV) experiments were carried out using both 2D-2C PIV and 2D-3C stereoscopic PIV acquisitions in order to study the influence of the third component. Thirdly, the snapshot proper orthogonal decomposition technique (POD) was applied to both measurements in order to analyse the reveal of the large-scale structures in the jet. The combination of (PIV & SPIV) and POD analysis showed that it is possible to isolate a few typical patterns from the apparently chaotic fluctuations of the jet. Moreover, the time variation of the POD modes was analysed by projecting the time-resolved data series onto the orthonormal basis derived from the POD. The results showed that, for both acquisitions, the first two modes represent the large-scale vortices responsible for the convection phenomenon. The results of the POD modes were similar for both campaigns, with the appearance of an additional mode representing the z fluctuations. The results also showed that the convergence of the energy of the flow was slower by considering the three components of the velocity field. In fact, for a 2D-3C POD, 198 modes were needed to obtain 90% of the total energy, while 61 modes were sufficient for a 2D-2C POD to obtain the same total energy.