Abstract
This paper reports on the measurements of wall shear stress and static pressure along a smooth static wall upon which jet impingement occurs. The effect of a single circular jet, respectively an array of jets is studied using a high speed/resolution camera. The areas of interest are the stagnation region and the wall jet region, where the jet is deflected from axial to radial direction. The effect of increasing the distance between the inlets is also investigated. The results are obtained by performing direct flow experimental visualizations and CFD numerical simulations, using the Reynolds averaged Navier-Stokes (RANS) approach with the commercial software ANSYS Fluent. The findings suggest that the smaller the nozzle-to-wall distance is, the higher the pressure peak. The wall shear stress has a bimodal distribution; at stagnation point, the wall shear stress is 0. An increase in the number of inlets produces the effect of a decrease in the stagnation point pressure. The greater the inter-inlet distance is, the greater the stagnation point pressure (there is less inter-jet mixing, less energy is lost in vortices formed between jets).
Highlights
The study of impinging jet flows (IJF) has been prompted by the late 1950s efforts to design a vehicle capable to withstand high atmospheric entry temperatures – the high heat transfer coefficient of jets impinging on a solid surface make them the ideal solution for this problem
The analysis consists in evaluating the behaviour of the wall static pressure pp and wall shear stress σσww distributions along the different regions of the jet
The inter-inlet distance has no influence on the maximum static pressure value; it does influence the point on the plate where this maximum is reached: the higher the distance is, the farther along the plate the pressure peaks
Summary
The study of impinging jet flows (IJF) has been prompted by the late 1950s efforts to design a vehicle capable to withstand high atmospheric entry temperatures – the high heat transfer coefficient of jets impinging on a solid surface make them the ideal solution for this problem. The diversification of IJF applications can be attributed to their ability to control the heat transfer by changing parameters like nozzle diameter, the nozzle-to-wall distance, the number of nozzles, the surface geometry, etc. With the arrival of Computational Fluid Dynamics (CFD) software, the governing equations of the flow could be solved numerically by dividing the fluid volume into grids of discrete elements and finding the velocity and pressure in each node. When a jet fluid exiting a nozzle encounters a flat plate, its behaviour changes – the impingement wall influences the flow parameters (like pressure and velocity). The analysis consists in evaluating the behaviour of the wall static pressure pp and wall shear stress σσww distributions along the different regions of the jet. By setting different values for these parameters, the effects they have on the static pressure and wall shear stress distributions are quantified. A comparison between the experimental and CFD results is performed, in order to assess the validity of the model chosen and the accuracy of the CFD results
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