Abstract
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 2.46 D j , 1.64 D j , and 0.82 D 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.
Highlights
The impinging jet configuration has received many considerations from researchers due to its widespread use in many industrial applications
The objective of our study is to investigate the flow characteristics of under-expanded turbulent jets impinging on a solid surface with various nozzle pressure ratios (NPRs) ranging from 2 to 2.77, and different values of nozzle-to-plate gaps
The mean axial velocity profiles obtained at low NPRs had maximum values along the jet centerline, while those at high NPRs showed the maximum velocity along the nozzle perimeter
Summary
The impinging jet configuration has received many considerations from researchers due to its widespread use in many industrial applications. The flow characteristics of impinging jets, despite the geometrical simplicity, are very complex and have posed challenges to numerical simulations, for turbulence modelling (Hadžiabdić and Hanjalić [2]). The jet flow configurations discussed in this paper are under-expanded, subsonic and supersonic free jets, i.e., jets exhaust in a quiet medium, and jets impinging on a solid surface, that are commonly found in aerospace engineering applications and turbomachinery systems. The flow configuration of supersonic impinging jet has rich and complex flow structures (Henderson [9]) that are originated from the compressibility and turbulent flows (Weightman et al [10]). The supersonic impinging jet is a highly resonant flowfied that is governed by a well-known aeroacoustics feedback loop (Weightman et al [10], Uzun et al [11], Akamine et al [12]).
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