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工程水力计算中的弯管局部阻力系数多为经验值,取值因来源不同而相差数倍,直接影响水力损失计算精度和工程造价。以90°圆弧弯管为研究对象构建模型,采用不同粗糙度钢管试验验证了三种k-ε紊流模型的正确性,在工程常用雷诺数范围3.2×104≤Re≤3.2×107和相对粗糙度范围0≤Δ/D≤0.002,模拟计算了不同相对粗糙度和雷诺数组合下的200余种工况的局部阻力系数。结果发现局部阻力系数与沿程阻力系数有类似的分区特征,存在光滑区、过渡区和粗糙区。在光滑区,局部阻力系数与雷诺数呈幂函数递减;在过渡区,局部阻力系数与雷诺数和相对粗糙度均有关;在粗糙区,局部阻力系数与相对粗糙度正相关,与雷诺数无关。局部阻力的影响长度在光滑管内随雷诺数增大呈非线性递增,在光滑管以外,随雷诺数的增大先递减然后趋于稳定,与相对粗糙度呈负相关。局部阻力系数与沿程阻力系数之间有一定函数关系,函数系数的变化仅与相对粗糙度有关。研究结果可为弯管局部损失的估算提供参考。
The local resistance coefficient of the elbow in hydraulic calculation of the project is mostly empirical value, the value varies several times due to different sources, which directly affects the calculation accuracy of hydraulic loss and construction cost. The model of 90 ° circular arc pipe was taken as the research object. The correctness of the three kinds of k-ε turbulence models was verified by experiments with different roughness steel pipes. In the common Reynolds number range 3.2 × 104≤Re≤3.2 × 107 and relative Roughness range 0≤Δ / D≤0.002, the local resistance coefficients of more than 200 kinds of working conditions with different relative roughness and Reynolds number are simulated. The results show that the local resistance coefficient is similar to that of the resistance coefficient along the path, with smooth zone, transition zone and rough zone. In the smooth zone, the local resistance coefficient decreases linearly with the Reynolds number. In the transition zone, the local resistance coefficient is related to the Reynolds number and the relative roughness. In the rough zone, the local resistance coefficient is positively correlated with the relative roughness but not with the Reynolds number . The length of influence of local resistance increases non-linearly with the increase of Reynolds number in smooth tube. Outside smooth tube, it decreases first and then stabilizes with Reynolds number increasing, and negatively correlates with relative roughness. There is a certain functional relationship between the local resistance coefficient and the resistance coefficient along the path. The variation of the functional coefficient is only related to the relative roughness. The results can provide a reference for the estimation of local loss of elbows.