Effects of Nozzle Pressure Ratio and Nozzle-to-Plate Distance to Flowfield Characteristics of an Under-Expanded Jet Impinging on a Flat Surface

The current work experimentally investigates the flowfield characteristics of an under-expanded turbulent jet impinging on a solid surface for various nozzle-to-plate distances 2.46D(j), 1.64D(j), and 0.82D(j) (D-j is the jet hydraulic diameter), and nozzle pressure ratios (NPRs) ranging from 2 to 2.77. Planar particle image velocimetry (PIV) measurements were performed in the central plane of the test nozzle and near the impingement surface. From the obtained PIV velocity vector fields, flow characteristics of under-expanded impinging jets, such as mean velocity, root-mean-square fluctuating velocity, and Reynolds stress profiles, were computed. Comparisons of statistical profiles obtained from PIV velocity measurements were performed to study the effects of the impingement surface, nozzle-to-plate distances, and NPRs to the flow patterns. Finally, proper orthogonal decomposition (POD) analysis was applied to the velocity snapshots to reveal the statistically dominant flow structures in the impinging jet regions.