高比转数离心泵空化状态下的压力脉动特性

Pressure pulsation characteristics of down-scaled high specific speed centrifugal pump under cavitation state

通过相似变换得到高比转数离心泵缩小模型,并通过试验和数值模拟发现模型泵和设计泵的性能曲线相近,可代替设计泵进行试验研究.基于RNG k-ε湍流模型,采用SIMPLEC方法求解不可压缩时均方程,通过对离心泵内部流场进行定常和非定常数值模拟,得到不同工况点的外特性、汽蚀及压力脉动特性,并通过模拟结果和试验结果的对比,验证了模拟的准确性.通过模拟发现:额定流量下隔舌处的压力脉动幅值最大;不同工况下各监测点的压力脉动主频均为叶频;隔舌压力脉动最大,进口压力脉动最小.额定工况下压力脉动幅值最小,非设计工况下压力脉动幅值明显增大;通过对空化不同阶段的瞬态数值模拟,发现从未空化到严重空化,不同工况下隔舌和出口处的压力脉动变换规律相同,随着空化发展,压力脉动幅值降低,且脉动主频均为叶频;并且随着空化程度加剧,压力脉动高频成分增多,各监测点主频下降明显,并可将此作为判定空化初生的依据.

The down-scaled model pump of a high specific speed centrifugal pump was obtained by using the affinity laws for centrifugal pumps.It turned out that the performance curve of the model pump is similar to the original scale pump based on experiments and numerical simulations,and the model pump can replace the original pump for experimental study.Based on the RNG k-εturbulence model,the incompressible time-average N-S equations of the fluid flow in the pump model were solved by SIMPLEC method.The hydraulic,cavitation performance and pressure pulsation characteristics of the pump under different operating conditions were obtained by steady and transient numerical simulations of the flow field in the pump.The accuracy of simulation was validated by comparing the simulated results with the experimental observations.In terms of simulation,the largest pressure pulsation amplitude is seen at the tongue at the rated flow rate.The dominant frequencies of pressure pulsation at each monitoring point under different working conditions are blade passing frequency.The tongue experiences the largest pressure pulsation,but the impeller inlet is subject to the smallest pressure pulsation.The pressure pulsation amplitude is the smallest under the rated flow rate condition,but significantly increases under off-design conditions.Through the transient numerical simulation at different stages of cavitation,it is found that from non-cavitation to severe cavitation,the pressure pulsation cha-racteristic in frequency domain on the tongue and at the outlet remains unchanged under different wor-king conditions.Specially,the pressure pulsation amplitude decreases with cavitation development,and the dominant frequency of the pulsation is the blade passing frequency.And with extending cavitation degree,the high frequency components in the pressure pulsation become rich,and the dominant frequency at each monitoring point drops off significantly.These outcomes can be used as the basis for judging cavitation inception.