基于动网格模拟的PVC球阀水流瞬态流动特性分析

Transient Flow Characteristics Analysis of PVC Ball Value Based on Dynamic Mesh

为了探讨PVC球阀瞬态流动特性,对DN50球阀进行试验和数值模拟,动网格模拟得到试验有效验证。结果表明,PVC球阀局部阻力系数与相对开度呈幂函数单调递减,流量系数与相对开度呈幂函数单调递增的关系,开度50%~60%是关系曲线变化拐点。当关闭到80%开度以下,阀芯内部和阀后流场产生漩涡和回流现象,阀芯入口和出口处形成高速区域,流动方向变化引起阀后流体质点分离和掺混,涡量和湍动能随开度减小而增大,50%开度以下产生较大局部阻力损失和阀后局部负压。拟合了阀前压力与关闭时间的表达式,两者呈e指数函数关系,为防止关阀引起水锤,建议关阀时间t≥4 s。

In order to analyze transient flow characteristics of PVC ball in the irrigation,the test and numerical simulation of PVC DN50 ball were carried out,the dynamic mesh simulation was also validated by experiments. The result show that the power function model was adopted to related the flow coefficient and local resistance coefficient with the opening of the ball valve,the first curve was monotonically increasing,and the second curve was monotonically decreasing,the opening of 50% ~ 60% is the inflection point of the curves,the relationship could be used to predict the flow characteristics in closing of PVC ball valve. When closed 80% opening of ball value,the phenomenon of whirlpool forms and back flow were happened in valve flow field,a highspeed region was formed at the inlet and outlet of the valve core,and the change of flow direction leads to the separation and mixing of fluid particles behind the valve. The vorticity and turbulent kinetic energy turned more with decreasing of the opening,the greater resistance loss and negative pressure formation behind the valve below 50% opening. The e exponential function was fitted between the valve pressure and closing time,in order to prevent water hammer caused by closing valve,it is suggested that closing PVC ball valve time at least more than four seconds.