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

摘要

The current work experimentally investigates the flowfield characteristics of anunder-expanded turbulent jet impinging on a solid surface for various nozzle-to-plate distances2.46Dj, 1.64Dj, and 0.82Dj (Dj is the jet hydraulic diameter), and nozzle pressure ratios (NPRs)ranging from 2 to 2.77. Planar particle image velocimetry (PIV) measurements were performedin the central plane of the test nozzle and near the impingement surface. From the obtained PIVvelocity vector fields, flow characteristics of under-expanded impinging jets, such as mean velocity,root-mean-square fluctuating velocity, and Reynolds stress profiles, were computed. Comparisonsof statistical profiles obtained from PIV velocity measurements were performed to study the effectsof 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 thestatistically dominant flow structures in the impinging jet regions.