冲击高度对半封闭紊流冲击射流流场影响的实验研究

An Experimental Study for the Effect of Nozzle-to-Plate Space on the Semi-Confined Turbulent Impinging Jet Flow

采用热线风速仪给出了在半封闭、雷诺数为 2 30 0 0时四种不同的冲击高度下紊流冲击射流流场的详细的测量结果 ,并与文献结果作了比较 .表明壁面的“阻尼”影响主要集中在近壁面 0 .5 D以内 ,在径向上流动既有顺压梯度 ,又有逆压梯度 .小板间距时径向速度曲线下降得比大板间距时明显要快 ,且曲线的峰值也稍大 ;在 r/D≤1 .0的区间内 ,板间距为 2和 4时紊动能的数值大小和分布趋势与板间距为 6和 8时的不同 ,在其它位置紊动能的分布趋势基本一致 ,只是大板间距下的值较大 ;流动结构在z4和 z6之间发生了较大的变化 ,这种变化与势流核心区有关 ,在势流核心区的顶端以及下游的一段距离内紊流度都很高 .

By using the IFA 300 Hot Wire/Film Anemometer, a detailed measurement for the effect of nozzle to plate space on the semi confined turbulent impinging jet flow field is obtained. In the experiment the Reynolds number considered is 23000, and the confinement wall is set 2D (D is the diameter of the pipe), 4D,6D,8D above the impingement wall respectively. The results for Z/D =2 are compared with those from LDV in the literature. It is shown that the “damping” effect mainly exists in the zone of 0.5D from the impingement wall, and there are positive as well as adverse pressure gradient in the radial direction. It is found that under small nozzle to plate space, the radial velocity decreases more rapidly than that under the large one, and that the peak of the velocity under the small space is a little larger. While in the r/D1.0 area, the trend and the quantity of the turbulent kinetic energy are much different from each other. For the other radial positions, the trend is the same though the quantity under the large space is a little greater. The experiment also shows that the flow structure has been greatly changed when the nozzle to plate space varied from Z/D=4 to Z/D =6 , which is due to the effect of the potential core of the jet. Consequently, the turbulent kinetic energy keeps a high value at the end of the potential core and in the area of several diameters downstream of it.