| As a unique flow phenomenon with high impact effect,impinging jet not only has abundant engineering application background,such as jet cutting and grinding,jet surface cleaning,large space jet ventilation system,jet element and so on,therefore,impinging jet has high theoretical research value.In the air conditioning design of large shopping center,industrial buildings and other places of high floor height,the airflow organization directly determines the energy utilization and comfort.For mine,tunnel,subway and other places of large depth,jet ventilation system can control the pollutant concentration,provide fresh air,to ensure the air quality.And jet elements have been widely used in various industrial control fields because of its advantages.Due to the strong shear,flow separation and impingement caused by the high pressure and high speed in its small-scale space,the instability of the flow may affect the stability of the control.Therefore,this paper will study the characteristics of close impinging jet on flat plate model obtained from the simplified jet element,and master the vortex flow characteristic and its influencing factors.To study the flow structures of submerged impinging jets under the condition of a very small impinging distance,the particle image velocimetry(PIV)technique was used to measure the flow field in the clearance and its surrounding region.In the experiment,the flow fields of six nozzle-to-wall distances(2 mm to 10 mm)and five volume flow rates varying from 0.1 to 0.5 L/min were measured.The intuitive images of vortex systems in the clearance were captured,and the evolution of the flow structure and flow characteristics with the variation of the impinging parameters were analyzed and summarized.Proper orthogonal decomposition(POD)analysis was employed to analyze the flow field measurement data to determine the main flow structure and the contributions of different energy modes to the total energy.It was observed that the first 25 POD modes can be considered as the dominant flow modes,and contain about 85% of the total kinetic energy of the flow.To determine the influences of jet parameters on pressure distribution,pressure probe technology was used for experimental measurement under some working conditions as examples.The results show that the jet parameters only affect the pressure within 3 times the diameter of the nozzle,but have little effect on the pressure at the measuring point outside the range.Through the numerical simulation of Reynolds similar amplification model,the prediction ability of various simulation methods on the flow field at the jet clearance is compared,and the large eddy simulation(LES)method is more suitable for the clearance flow field numerical simulation of impinging jet on plate according to the similarity analysis between the simulation result and the experimental result.The large eddy simulation method is used to solve the prototype of jet elements,and the structure of vortex system in submillimeter scale is obtained in real working conditions.The results show that the improper parameter matching can lead to the self-excited oscillation of the jet and lead to the decrease of its stability. |
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