Turbulent transport in a planar jet with self-sustained deterministic oscillations and the character of impinging region heat transfe

The objective of this study was to investigate the momentum and thermal energy transport enhancement in a planar jet with self-sustained oscillations. The cases studied included a full investigation of the free jet and impingement cooling performance when the free unsteady jet flow was obstructed by an impingement plate. The governing equations were analyzed using triple decomposition of instantaneous flow quantities. It was found that in addition to the molecular viscous stress, conduction heat flux, turbulent Reynolds stress and turbulent heat flux, there existed oscillation stress and oscillation heat flux in the governing equations. These additional inertia terms were unique in the flows with deterministic oscillations. It was also found that oscillation stress and heat flux contributed to the transport enhancement process due to oscillation. Flow field in an oscillatory plane jet with self-sustained oscillations was studied using an unsteady flow model. The corrected similarity solution was validated by measurements and showed that the prediction of the instantaneous deterministic part of the flow field could be calculated with reasonable accuracy. A modified full velocity, yaw angle crossed hot wire calibration was implemented in order to realize the triple decomposition. Detailed flow field measurements were performed to obtain the instantaneous flow quantities. The transport of momentum and kinetic energy in the similarity region of oscillatory free jet flow was presented. The heat transfer character of a cold oscillatory jet impinging on a hot metallic surface was investigated. First, non-oscillatory impinging jet heat transfer data were obtained as a steady state baseline. Second, the jet was oscillated fluidically at a fixed frequency. The comparison of results from the two cases showed that the heat transfer coefficients were greatly augmented by the oscillation of the jet. In the center region, the Nusselt numbers for a Reynolds number of 14,000 were increased as high as 75%. In the outer region of the impingement plate, the enhancement was 17-20%. The Nusselt number distribution curve of the oscillation jet impingement was fuller, at a level higher than that of steady counterpart.