双进口两级双吸离心泵过渡流道压力脉动特性研究

摘要

双进口两级双吸离心泵的过渡流道由正流道、过桥段、反流道3部分组成,其中正流道为双蜗壳型式,反流道为带有导叶的双螺旋型式,过桥段连接正反流道呈现空间扭曲状.过渡流道与首级叶轮和次级叶轮均存在动静耦合关系,由此导致的动静干涉效应是引起压力脉动的主要根源之一.采用CFD方法对双进口两级双吸离心泵典型工况下的三维非定常流场进行了研究,对过渡流道压力脉动机理进行了分析.研究发现,正流道内的静压分布与其双蜗壳型式密切相关,在所有工况下均呈180°对称分布,压力脉动主频均为叶片通过频率,最大脉动幅值均出现在隔舌附近;小流量工况下,隔舌处压力脉动主频幅值明显高于设计工况,约为设计工况的180％.在过桥段中,所有工况下压力脉动主频均为叶片通过频率,设计工况下,沿着流动方向,内壁面进口处的压力脉动主频幅值达到最大,外壁面主频脉动幅值变化沿流动方向有增加的趋势;在反流道中,设计工况下压力脉动主频为叶片通过频率,幅值沿着流动方向逐渐增加,出口处主频的脉动幅值约为进口处的110％;小流量工况下,反流道导叶附近存在低频成分,且在导叶周围发现具有周期性的漩涡.%Double-inlet two-stage double-suction centrifugal pump is a new type of pump,which has large flow rate and high head.The inter-stage flow channel of a double-inlet two-stage double-suction centrifugal pump is located between the first-stage single-suction impeller and the second-stage doublesuction impeller.It is divided into forward channel,bridge and reverse channel.The rotor-stator interaction between the inter-stage flow channel and the impellers may be one of the main causes of pressure fluctuation.The forward channel is twin-volute type,and the reverse channel is double spiral type with a guide vane.The bridge is three dimensional distortion connecting the forward channel and reverse channel.The three-dimensional unsteady flow field of double-inlet two-stage double-suction centrifugal pump is studied by using CFD method,and the pressure fluctuation mechanism is analyzed.In the forward channel,the static pressure distribution is closely related to twin-volute type with 180° symmetric distribution under all flow conditions.The blade passing frequency is the main frequency of pressure fluctuation,and the maximum amplitude appears near the tongue.Under low flow rate conditions,the main frequency amplitude of pressure fluctuation is significantly higher than that under design conditions,which is about 1.8 times as that under design conditions.In the bridge area,the main frequency of pressure fluctuation is blade passing frequency under all the conditions.Under design condition,the main frequency of pressure fluctuation of inlet of the inner surface reaches the maximum along the flow direction,while that of outer surface has the reverse rule.In the reverse channel,the main frequency of pressure fluctuation is the blade passing frequency under design conditions,whose amplitude along the flow direction is gradually increased.The fluctuation amplitude in the outlet is about 1.1 times as that in the inlet.Under low flow rate conditions,the low-frequency component and the periodic vortex nearby the guide vane are found.The research result provides a basis for improving the hydraulic design and the operation stability of double-inlet two-stage double-suction centrifugal pump.