渐缩渐扩洞塞消能和空化特性

Energy dissipater and cavitation characteristic study on gradual contraction and expansion discharge

建立了三维RNG k-ε紊流数学模型和突缩突扩洞塞泄流的物理模型试验,利用实验结果对数学模型进行了验证,利用验证后的数学模型对突缩突扩洞塞和渐缩渐扩洞塞的水头损失系数和空化数进行了计算。结果表明,洞塞渐缩(或渐扩)段相对长度一定时,随着渐扩(或渐缩)段相对长度的增加,水头损失系数减小,最小空化数增加。当渐缩段和渐扩段几何尺寸互换时,水头损失系数和最小空化数的变化不大;其他几何参数一定的情况下,随着横断面半径收缩比的减小,水头损失系数增加,最小空化数降低。圆弧连接情况下,随着圆弧夹角的增加,水头损失系数呈现先降低后增加的趋势;而最小空化数呈现先增加后降低的趋势。其他几何参数一定的情况下,圆弧连接的水头损失系数小于斜线连接的对应值,最小空化数则相反。在水头损失系数和最小空化数权重相等的假定条件下,初步探讨了渐缩渐扩洞塞几何体型参数的优化方法,给出了渐缩渐扩洞塞的最优几何体型参数。

Turbulence characteristics of sudden contraction and expansion discharge and gradual contraction and ex-pansion discharge were analyzed respectively. A 3-D RNG k-ε turbulent model and a physical model were employed, respectively, and the computational results of turbulent model were validated by the physical model data approximate-ly. Then the turbulent model was adopted to compute the head loss coefficient and the cavitation number. The results showed that under the given length of gradual contraction/gradual expansion, with the increase of gradual expansion length/gradual contraction length, the head loss coefficient decreases and the minimum cavitation number increases respectively. When the gradual contraction length exchanges with the gradual expansion length, head loss coefficient and minimum cavitation number vary little respectively. With the decrease of radius ratio of cross section, the head loss coefficient increases and the minimum cavitation number decreases respectively. As far as the arc connection is concerned, with the increase of arc angle, the head loss coefficient decreases firstly and then increases, but the mini- mum cavitation number increases firstly and then decreases. The head loss coefficient of arc connection is less than the oblique line connection does, and the minimum cavitation number of arc connection is more than the oblique line con- nection does. With the equal weight assumption of head loss coefficient and minimum cavitation number, an optimiza-tion method of gradual contraction and expansion parameters was discussed preliminarily, and the optimal geometry parameters were obtained.