单流道离心泵定常非定常性能预测及湍流模型工况适用性

Performance prediction of single-channel centrifugal pump with steady and unsteady calculation and working condition adaptability for turbulence model

为了评价计算流体动力学在单流道离心泵性能预测中的精度,以一台比转速为140的单流道离心泵作为研究对象,基于试验测试结果,对比分析了定常及非定常计算方法的性能预测结果,研究了标准k-ε湍流模型(Standard k-ε)、重正化群k-ε湍流模型(Renormalization group k-ε,RNG k-ε),标准k-ω湍流模型(Standard k-ω)和SST k-ω湍流模型(Shear stress transport k-ω,SST k-ω)4种湍流模型在单流道离心泵内流计算中的适用性,并分析了泵内的流动。结果表明,单流道离心泵内流的CFD计算应采用非定常方法;小流量工况下,单流道泵的内流CFD(Computational fluid dynamics)计算应采用SST k-ω模型,扬程、效率和功率偏差均比较小,分别为0.38%、3.12百分点和5.59%;设计工况和大流量工况下的内流计算应采用RNG k-ε模型,扬程预测偏差在3%以内,效率预测偏差在4个百分点以内,功率预测偏差在4%以内;小流量工况时,单流道叶轮叶片进口边下游压力面流道内出现较严重的流动分离和回流现象;单流道叶轮出口环面的低压区位置位于叶片出口边上游,且紧靠出口边。研究结果可为单流道离心泵CFD性能预测提供参考。

In order to evaluate the performance prediction accuracy of single-channel pump under computational fluid dynamics, a single-channel pump was taken as the study object. The standard k-ε, RNG k-ε(renormalization group k-ε), standard k-ω and SST k-ω(shear stress transport k-ω) were used to predict the performance of single-channel pump numerically. Meanwhile the grid dependence was checked by employing 5 sets of meshes to improve the computational accuracy. The results of steady and unsteady numerical simulation were compared with that of the experiment on the head and efficiency. The unsteady results were closer to the experimental value. Therefore, the unsteady simulation method should be applied to simulate the internal flow of the single-channel pump. The head, efficiency and power were predicted under 3 different discharges(0.6 Qd, 1.0 Qd, 1.4 Qd, Qd is flow rate on design operating conditions, 220 m3/h) by using CFX(computational fluid dynamics X) 14.0. Energy performance prediction error was analyzed by compared with experimental results. The results showed that there was different degree error between the performance prediction values of the different turbulent models and experimental values. For head prediction of the discharge of 0.6Qd, the standard k-ω model, compared with the other 3 models, had higher prediction accuracy and the head error was 0.008%, followed by the SST k-ω model. However, for efficiency prediction of the discharge of 0.6 Qd, the SST k-ω model had the minimum error value. Therefore, for the simulations at low flow rates, head, efficiency and power errors were 0.38%, 3.12 percentage points and 5.59% respectively with the SST k-ω model. At the design condition, while the head calculation results of the RNG k-ε model were closer to the experimental results than other turbulent models, the standard k-ε model got the best results for the efficiency calculation. The efficiency error of the RNG k-ε model was about 0.1 percentage points lower than the standard k-ε model, so the RNG k-ε model was applied to performance prediction under the design operating condition. When the single-channel pump was operating at the large flow condition(1.4Qd), the RNG k-ε model possessed the highest precision of the head prediction and the standard k-ε model was the best in the efficiency prediction. For comprehensive evaluation of the data, among all 4 turbulent models the RNG k-ε model was the best one to predict the performance of single-channel pumps at the large flow rate. For the internal flow simulation of single-channel pump, the flow separation existed on the blade pressure surface under various operating conditions. As the decrease of the flow rate, the flow near the inlet edge tended to be disordered, especially with a wide range of backflow at the low flow rate. At the same time, there was large backflow on interior areas of the blade pressure surface. There were stagnation points near the inlet edge of blade suction surface and on the backboard. However, serious separation and recirculation flow would occur within the flow passage of the blade pressure side under the low flow conditions. Low pressure on the ring surface of impeller outlet was upstream to the blade outlet and near the outlet. The conclusions in this paper will provide a reliable performance prediction data and practice basis for the single-channel pump, also point the way for developing turbulent models for further study of single-channel pumps.