离心泵蜗壳内非定常流动特性

Characteristics of unsteady flow in a centrifugal pump volute

基于修正的RNG k-ε湍流模型和输运方程空化模型,对离心泵内部非空化和空化的非定常流动进行了数值模拟,计算结果与试验结果吻合较好,验证了数值模型和计算方法的准确性。在离心泵蜗壳内布置了5个监测点,分析了蜗壳内非空化和空化工况时流动特性。结果表明:离心泵非空化和临界空化工况下,蜗壳内压力脉动的主频为叶片通过频率145 Hz或290 Hz,而在充分发展空化工况下,压力脉动的主频非常低,可能原因是空泡剧烈的脱落及溃灭引起的。三种工况下,离心泵蜗壳第2断面附近的压力脉动最大幅值均远大于其它监测点,原因是此处存在较强的二次流,出现了两个非对称反向旋涡,两个旋涡的涡心位置、形状、强度随时间不断变化,对流动产生较强扰动,诱发强烈的压力脉动。

The unsteady flow in a centrifugal pump was numerically simulated by using combination of the modified RNG k-ε turbulence model and the transport equation cavitation model.The agreement between the experimental results and the simulation ones was satisfactory,it demonstrated that the numerical model and the calculation methods can be used to accurately predict the cavitation flow in a centrifugal pump.The flow characteristics in a centrifugal pump volute without and with cavitation were analyzed by setting 5 monitoring points in the volute.It was shown that the dominant frequencies of pressure fluctuation in the volute at operating conditions of non-cavitation and critical cavitation are the blade pass frequency of 145 Hz or 290 Hz; however,the dominant frequency of pressure fluctuation at the developed cavitation condition is very low due to the violent shedding and collapse of bubbles in the pump; for three operating conditions,the maximum amplitude of pressure fluctuation at the second section of the volute is much larger than those at other sections,the possible reason is that there is a strong second flow near this section induced by a pair of counterrotating vortex; the location,shape and strength of the vortex are changing with time,this changing vortex disturbs the flow in the second section and leads to strong pressure fluctuations.