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

Abstract

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.

Keywords

• under-expanded impinging jet
• velocity measurements
• particle image velocimetry
• proper orthogonal decomposition