空化诱导的离心泵叶轮区流动特性与压力脉动分析

Analysis of Flow Characteristics and Pressure Pulsation in Impeller Region of Centrifugal Pump Induced by Cavitation

摘要:

空化是一种复杂的多相流现象，空化发展中液体和蒸汽之间瞬态相变的产生，导致多尺度旋涡运动。瞬态空化动力学与空化涡结构的演化密切相关。采用对比结合Q准则、Omega判别法两种涡识别方法，探究设计流量Qd为0.321 m3/s下不同空化程度时离心泵叶轮区的空泡、涡旋特性及其对压力脉动的影响。基于Schnerr-Sauer空化模型对立式单级单吸蜗壳式离心泵在空化初始阶段、空化发展阶段、空化状态转变阶段、空化恶化阶段4个不同空化程度时的全流道流场进行数值模拟分析。结果表明，空化情况下叶轮区域流动复杂，空泡形态与旋涡的生成变化相互影响，二者共同影响叶轮域内压力脉动的变化。Omega方法能够精准捕捉到叶轮进口的回流涡、叶轮流道内通道涡和叶轮尾缘处的尾迹涡;空化初期，受通道内大面积通道涡及蜗壳隔舌动静干涉的影响，出现各叶片上空泡大小不同的情况;空化严重时受空泡脱落影响出现气液混合的高速涡团，导致低频压力脉动信号增加，空泡移动至高压区溃灭释放的能量导致出口压力脉动显著升高。

Abstract:

Cavitation is a complex multi-phase flow phenomenon. In the development of cavitation, the transient phase transition between liquid and steam results in multi-scale vortex motion. The transient cavitation dynamics is closely related to the evolution of cavitation vortex structure. Two vortex identification methods, Q criterion and Omega discriminant method, were used to explore the cavitation and vortex characteristics of centrifugal pump impeller region and their effects on pressure pulsation under different cavitation degrees at rated flow Qd=0.321 m3/s. Based on Schnerr-Sauer cavitation model, the full-channel flow field of vertical single-stage single-suction volute centrifugal pump at four different cavitation degrees, including the initial stage of cavitation, the development stage of cavitation, the transition stage of cavitation and the deterioration stage of cavitation was numerically simulated. The results showed that the flow in the impeller region was complex under cavitation conditions, and the cavitation morphology and vortex formation affected each other, and both influenced the pressure pulsation in the impeller region. The Omega method can emotionally capture the reflux vortex at the inlet of the impeller, the passage vortex in the impeller channel and the wake vortex at the trailing edge of the impeller. In the early stage of cavitation, due to the influence of large-area channel vortices and volute tongue in the passage, the size of the bubbles above each blade was different. When cavitation was severe, high-speed vorticity of gas-liquid mixture appeared under the influence of cavitation loss, resulting in the increase of low-frequency pressure pulsation signal, and the energy released by the cavitation moving to the high-pressure area led to a significant increase in outlet pressure pulsation.