提升离心泵小流量工况数值模拟精度的进口边界设置

为提高离心泵小流量工况下性能参数的预测精度,参考关死点工况数值模拟研究的现有文献,将一种开口边界作为吸水管进口条件应用于某离心泵的多个小流量工况,以试验测量结果为基准,与常规进口边界设置下的计算结果进行了性能参数及泵内流场的对比分析,研究了不同边界设置对于不同工况的适用性。结果表明:以吸水管进口处是否存在回流为判别标准,对于存在明显回流的工况,采用开口边界可以大幅提升扬程等性能参数的预测精度,而对于入流均匀无回流的工况,常规边界条件即可满足工程计算精度要求;采用开口边界可以在吸水管进口处释放回流而避免形成虚假漩涡,保证水力损失的合理预估,进而得到更为精确的离心泵特性曲线。因此,在计算离心泵的完整特性曲线时,可首先采用常规边界条件进行全工况的数值模拟,再根据进口回流情况调整进口边界设置,对少数小流量工况进行二次计算,确保特性曲线形状符合真实情况。

Inlet Boundary Settings for Improving Numerical Accuracy of Modeling Part-load Conditions of a Centrifugal Pump

In order to increase the accuracy of predicting pump performance in part-load conditions, an opening boundary was introduced as the inlet boundary for a centrifugal pump, which has been successfully applied on modeling shut-off conditions by other scholars. Using hydraulic test results as a benchmark, simulation results respectively with the opening boundary and the conventional inlet boundary were compared in aspect of performance parameters and flow field. Applicability of different boundaries for different conditions was discussed. The results show that whether there are backflows at the suction pipe entrance can be regarded as a mark for choosing the appropriate boundary setting. For conditions with evident backflows, using the opening boundary can greatly enhance the prediction accuracy for pump performance, while for conditions with uniform inflow and no backflows, the numerical accuracy with the conventional inlet boundary can meet the engineering requirements. The opening boundary release backflows at the suction pipe entrance to avoid generating fake eddies and ensure a reasonable estimation of hydraulic loss. Therefore, a good strategy to obtain correct performance curves of centrifugal pumps is that to conduct simulations widely within operation range first using the conventional inlet boundary and then check the flow state around the suction pipe entrance, and finally adjust the boundary setting to an opening one to recalculate the flow field for a few part-load conditions.