局部水头损失对流体瞬变的影响及其数值模拟

Influence and numerical simulation of local head losses on pressured conduit hydraulic transients

为了分析由水流内部结构发生变化而导致的局部水头损失对流体瞬变压力分布的影响,通过增加约束方程和引入能量损失修正系数,建立节点法和均分法2种包含局部水头损失的流体瞬变计算模型.采用数学模型对考虑局部水头损失情况下的流体瞬变进行数值模拟,得到等效节点瞬变压力变化过程、压力管道沿线最大水击压力的包络线、局部水头损失比重对沿程最大瞬变压力分布的干扰以及局部水头损失呈多点离散分布对沿程最大瞬变压力分布的影响.结果表明,局部水头损失会导致附近的瞬变压力和压力包络线的分布发生局部改变,但通常不会影响整个系统的最大瞬变压力值;对于所占比重较小并且呈离散分布的局部水头损失,采用修正系数法能够对压力管道的最大瞬变压力进行等价模拟.

A numerical model was established to analyze the influence of local head losses on pressured conduit hydraulic transients caused by changes Of the hydraulic grade line. Boundary equations and energy modification coefficients were presented in the model, and local head losses were distributed to the equivalent node or element. Transient pressures of the equivalent node with head losses were simulated by the numerical method, and the maximal pressure along the conduit was calculated. The calculation error was analyzed based on the proportion and distribution of local losses. Results showed that local head losses have influence on the contiguous node and pressure grade line except the maximal transient pressure and attenuation of both entrance and outlet nodes of the conduit, and that energy modification coefficients can be used conveniently to simulate conduit hydraulic transients with local losses, if the local losses scatter in the conduit and are smaller than friction losses.