梯形断面蜗壳式离心泵作透平叶轮的设计与试验

Design and Experiment of Impeller of Centrifugal Pump as Turbine with Trapezoidal Cross-section Volute

为提高非圆形断面蜗壳式离心泵作透平的效率,以一比转速为193的梯形断面螺旋形蜗壳式离心泵为原型,设计了适应此类泵作透平运行的透平专用叶轮。根据原型泵梯形断面蜗壳几何参数,依据面积相等的原则,推导梯形断面几何参数与当量圆断面半径的换算关系式;依据等速度矩定律确定叶轮进口速度矩,推导出叶片进口安放角与设计流量的关系表达式;对于叶片进口较宽的情况,在轴面投影图中划分三条流线,分别计算三条流线与叶片出口边交点处的出口安放角;基于ANSYS BladeGen与NX软件建立新叶轮的三维模型,制作试验叶轮,开展外特性试验,并进行数值模拟分析。结果表明:新叶轮将透平最高效率由71.9%提高到了77.3%,较原型叶轮透平最高效率提高了7.5%,且新叶轮在75~130 m^3/h的流量区间均能高于72%的效率运行,效率曲线较平坦,高效区运行范围宽。数值计算结果分析表明新叶轮进口能较好地适应螺旋形蜗壳的出流;从叶片进口到叶片出口,液体压能得以较均匀地转换,叶轮内的水力损失较原型泵叶轮内部显著减小。透平试验高效点与给定的设计流量一致,验证了该文提出的透平叶轮设计理论和方法是合理可行的。

In order to improve the efficiency of pump-as-turbine(PAT), a specific speed 193 centrifugal pump with noncircular section spiral volute is chosen as a research object and one kind of special impeller is designed for the turbine’s working condition. The relational expression between trapezoidal geometry characters and radius of equivalent circle is derived based on the area equal principle. The velocity moment at impeller inlet is acquired on the basis of constant velocity moment theory. And the relational expression between blade inlet angle and rated flow rate is derived. Considering the relatively large inlet width of blade, the blade axial projection draw is divided into two parts. Three outlet angles at the intersection of the three meridional streamline and blade trailing edge are calculated, respectively. The new special turbine impeller is modeled by using ANSYS BladeGen and NX software. The impeller is manufactured and the performance test is carried out on an open PAT test rig. To understand how the performance is improved, a verified computational fluid dynamics technique is adopted in the turbine mode performance prediction of PAT with the two impellers. The comparison of new impeller and the original PAT experimental results shows that the highest efficiency is raised from 71.9% to 77.3%. The best efficiency is increased by 7.5%. Compared with original PAT performance curves, the efficiency curve of PAT with new impeller is flat, and the high efficiency operating range of the special impeller is wider than that of the original impeller. The new impeller can adapt to large variation range of flow rate. The efficiency of PAT with new impeller is above 72% between 75-130 m^3/h operating ranges. Numerical calculation results show that the new special impeller blade inlet angle can match well with the flow of the spiral volute outlet. The energy transformation is more uniform from the blade inlet to the blade outlet in new impeller. Hydraulic loss analysis shows that the hydraulic loss within the new special impeller is significantly less than that of the original impeller at a high flow rate. The experimental best efficiency point is consistent with the given design flow rate. Thus, it is verified that the impeller design theory and method proposed in this paper is reasonable. Research results have important meaningful to enrich the PAT impeller design theory and method.