| By numerical modeling analysis, flow and acoustic characteristics of the confined jetimpinging on the wedge obstacle is studied in the thesis. Source of noise produced by theconfined impinging jet consists of two parts: the quadrupole source by the free jet sectionand the dipole source with the flow of fluid through the obstacle. Due to the effect of thenozzle diameter, the jet velocity，the size of the obstacle, its location placed in the flowfield and other factors, the noise produced by the confined impinging jet is complex.The steady-state numerical simulation of the confined jet is made by changing theparameters of the angle and the length of the obstacle. According to the simulation results,this jet is divided into three sections: free jet area, impact area and surface diffusion area.When the obstacle angle is small, the separated fluid will join together at the downstream.The split-flow divided by the obstacle can not converge together along with the obstacleangle increasing and the appearance of the wall jet become obvious. The length of theforce on the obstacle equal to the barometric pressure is increasing by the obstacle lengthand the property of the jet become more stable.By changing the position of the obstacle in the flow region, the unsteady flowcharacteristic of the confined jet is investigated by large eddy simulation (LES) approach.The simulation results reproduce the growing, separation and broken process of the vortexin the flow region. When the obstacle is located in the different positions, the vortex ringstructure is destroyed and the distribution of the quadrupole source is influenced. As thejet flow velocity varies with the different positions, the turbulent intensity is different.Taking the flow field fluctuating pressure of large eddy simulation as sound source,and using the FH-W equation numerically, the restricted jet far field’s acoustic noisepeculiarity is got. When obstacle is in the same position as flow field, and that the distancefrom the observation point to the nozzle is the same, the sound pressure level in x-axialdirection is always greater than y-axis’. When in the same direction of observation point,the sound pressure level at the observation point is decreased with the increase of thedistance. If observed in the same location, the sound pressure level will be highest whenthe obstacle is located at the10d of flow field, next is5d of flow field, and the soundpressure level will be the lowest at the15d of flow field. The sound pressure level is a result of several conditions as below: the distribution of free jet flow field velocity, thedistribution of free jet sound source, the position of the obstacles in flow field and theobstruction’s shape. |
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