叶轮进口条件对串并联离心泵无过载特性的影响

Effect of impeller inlet condition on non-overload performance of serial-parallel centrifugal pump

为了阐明叶轮进口条件对串并联离心泵无过载性能的影响,该文从速度三角形理论出发,引入进口速度加权平均角度(θ),推导了单级模型泵无压直管叶轮进口条件的最大轴功率,以及相对应的流量的计算公式。在此基础上,研究了串并联离心泵分别应用无压半螺旋和有压半螺旋2种不同叶轮进口条件对无过载性能的影响。结合(computational fluid dynamics,CFD)技术,对各模型泵外特性曲线进行了数值模拟,并搭建试验台分别对单级模型泵和串并联离心泵进行试验。分析表明:计算结果与试验结果能够较好地吻合,在设计工况下,扬程误差和功率误差均在5%以内,从而验证了数值模拟结果的正确性。结果证明:不同叶轮进口条件下,得到的轴向速度分布均匀度变化不大,均匀度较好;而流动偏移角(γ)值有较大的差异,γ值越大越有利于无过载性能的实现。该研究结果为串并联离心泵的无过载研究和开发提供了一定的依据。

Aiming at influences of different inlet flow on non-overload performance of Serial-Parallel Centrifugal Pump（SPCP）, establishment of accurate prediction methods is necessary. In fact, the motor of the pump can easily burn out when the pump is working with a large flowing capacity and a high head. A pump is deemed as one with non-overload characteristics when its motor power is larger than 120% of the max shaft power, therefore the non-overloaded characteristic analysis of the SPCP plays a significant role for the safe running of the pump. In this paper, the average angle of inlet velocity（^-θ）, which the impeller inlet flow distribution can be efficiently assessed, is firstly introduced to calculate the maximum shaft power（Pmax） of Single-Stage Model Pump（SSMP） in the case of impeller inlet about no-pressure straight pipe, and relevant flow（tQ′） formula based on velocity triangle theory. Then, having researched the applications of SPCP in the case of two different impeller inlets： No-pressurehalf spiral and pressurehalf spiral. Once more, Computational Fluid Dynamics（CFD） is used to simulate the external characteristic curve of each model, and the enclosed experiment settings are adopted to firstly conduct analysis on the single stage model pump and then on SPCP after modifying the inlet and outlet pipes. In conclusion, analysis indicates that the results of calculation and experiments coincide with each other well. Under the design condition, the head error and the power error are respectively 1.20% and 2.40%, and when the SPCP is in the serial working condition, the head error and the power error are respectively 3.80% and 4.10%; in parallel working condition, the head error and the power error are respectively 2.90% and 3.50%. Therefore, those head errors and power errors are less than 5%, which proves the correctness of numerical simulation. What＇s more, with the different inlet flow state, axial velocity is distributed uniformly with a little change while the value of γ, the angle between the speed vector of unit nodes and the axial-surface streamline, has a big change. By comparing the values of the γ in different working conditions, it can be found that the non-uniform flow in serial working status is more obvious than that in parallel working status. In addition, a.k.a. θ =γ, by putting these results into formulas, the theoretical tQ′ and Pmax values can be obtained, which are later compared with the experimental results. The tQ′ and Pmax values in non-overloaded working condition have much smaller errors when compared with experiment results, which are respectively 1.38% and 0.47% in the SSMP. However, when the SPCP is in serial working condition, it is easy to go overload. When StQ′ =78.10 m3/h, the pump is at its max power point; in parallel working condition, with PtQ′ =168.50 m3/h, the pump is at its max power point, since the volume of flow is double that of before, for single-stage single-suction centrifugal pumps, it has its max power point only when tQ′ =84.25 m3/h. In actuality, when the rated power of a SPCP motor reachesmotor maxP ≥P, e.g. motorP ≥ 56.64 kW, the pump can achieve its non-overloaded characteristics. This research shows an excellent theoretical innovation, holds a high perspective and provides theoretical reference for designing the hydraulic property of SPCP.