不同空化数下轴流泵叶顶间隙区空化特性

Tip Clearance Cavitation Characteristics in Axial Flow Pump under Different Cavitation Numbers

基于修正的SST k-ω湍流模型和空化模型,对叶顶间隙为0.5 mm轴流泵模型进行了数值计算,分析了不同空化数下叶顶区不同圆柱截面的空化面积、叶轮出口轴向速度以及叶顶区空泡体积分数等特性。数值计算与高速摄影试验结果表明,数值模拟方法准确预测了轴流泵NPSH曲线和叶顶区空化流场;轴流泵初生空化出现在叶顶区,其空化类型主要包括刮起涡空化、泄漏流空化、卷吸区空化及叶顶泄漏涡空化;在空化数为0.451时,叶顶泄漏涡具有明显的涡带空化特性,随着空化数的逐渐降低,叶顶泄漏涡卷吸区的空化范围逐渐扩展,并与泄漏流空化区连成一片,且空泡云扩展到整个叶片吸力面;在间隙泄漏流作用下,叶轮出口轴向速度在靠近间隙区域逐渐降低,并随着空化数减小,轴面速度进一步下降;在不同空化数下,叶片吸力面圆周截面空化面积系数从轮毂到轮缘先增大,在叶片中部达到最大值,然后迅速减小,在叶顶区由于受到间隙效应的影响,叶顶区空化面积迅速增大。

The cavitation flow field in the axial flow model pump with tip clearance 8 = 0.5 mm was simulated based on modified SST k-to turbulence model and cavitation model. The cavitation bubble distributions at different circumferential sections, meridional velocity distribution at impeller outlet and cavitation volume fraction were analyzed. Numerical and experimental results showed that the NPSH curve and.tip region cavitation flow were predicted successfully. Cavitation inception in axial flow pump oecured in the tip region, including blowing vortex cavitation, leakage flow cavitation, rolling region cavitation and tip leakage vortex cavitation. In the condition of cavitation number or = 0. 451, the tip leakage vortex induced obvious cavitation cloud. The cavitation range of rolling region expanded with the decreasing of cavitation number gradually, and merged with the leakage flow cavitation area, and finally extended the cavitation bubble cloud to the entire suction side of the blades. The meridional velocity at impeller outlet near the gap region decreased gradually, in the influence of the gap leakage flow, and was further declined with the decreasing cavitation number. In different cavitation conditions, the circumferential section cavitation area coefficient of the blade, ranging from the hub to the tip, increased primarily, nd decreased afterwards. In the tip region, cavitation area coefficient bursted to the peak and dropt rapidly.