Internal Clearance Flow And Its Excitation Characteristics In A Centrifugal Pump

Based on the wide application of centrifugal pumps in various fields, the stability of the pumps operation has been paid more and more attention. The vibration induced by flow is one of the main factors that affect the stability of centrifugal pump. There are many theoretical and experimental support for the effects of flow in the main flow component, and there is little research on the gap flow. The flow characteristics in the clearance of the centrifugal pumps will change its performance, and affect the pressure pulsation and vibration characteristics of the centrifugal pumps, so that the running state of the pump will be affected. Studying the clearance flow of the centrifugal pumps, which can obtain the internal flow characteristics and the induction rule of vibration noise, and provide reference for the study of the mechanism of flow induced vibration.This paper takes a low specific speed centrifugal pump as the research object. Respectively, using 0.25 mm,0.5 mm and 0.75 mm (with the impeller inlet diameter of 0.3125%,0.625%, and 0.9375% respectively) of the wear-ring. The steady and transient numerical calculations are carried out, and the performance, pressure pulsation and vibration test are carried out. The pressure field of the outer surface of the impeller is solved and analyzed, and the impeller radial force is obtained. The pressure fluctuation and vibration data of each monitoring point were measured, and make a preliminary exploration on the flow characteristics and excitation characteristics of the centrifugal pump clearance. The main work of this paper and the main conclusions are as follows:1) For the model pump that with clearance or without clearance, the steady and transient numerical simulation are carried out. From the results can be known: The performance curve of the case with the clearance model is slightly lower; The existence of the clearance that has a significant influence on the flow characteristics of the impeller, which makes it more complicated; In addition to the pressure fluctuations of the case with clearance on each part expect the tongue are higher; With the increasing of the flow rate, the radial force of the impeller decreases and then increases with the increasing of the wear-ring clearance; On the small flow and the design condition, the radial force of the impeller is not related to the wear-ring clearance; At large flow condition, the radial force of impeller increases with the increasing of the wear-ring. Under the design condition, the pressure fluctuation amplitudes on the inlet of the impeller and the inlet of the front cavity, the outlet of the impeller increase first and then decrease with the increasing of the wear-ring clearance. Under the design condition, the flow velocity and the vorticity of the front cavity fluid increase with the increasing of the wear-ring clearance.2) Pressure pulsation tests that based on the performance test of the pump is carried out by using the micro dynamic pressure sensor. From the results can be known:When the flow rate increases, with the increasing of the wear-ring clearance, the head lift decrease first and then increase; and the shaft power decrease slightly. The influence of the clearance on the pressure fluctuations of the pump can be changed with the changing of working condition. There is an optimum wear-ring size to minimize the pressure fluctuation amplitudes of the blade pass frequency (fBPF) under the design condition.3) Vibration measurement test on different wear-rings clearance is carried out, and the vibration signals of the pump casing and footing are obtained. From the results can be known:Both the partial and design condition in the 0-20000 Hz, effects of different wear-ring clearance on the vibration signal on the footing of test pump is nearly identical. Under the partial and design conditions, the acceleration of vibration decreases and then increases at the 8 times of the fBPF with the increasing of the wear-ring clearance. In the second section of the volute, the acceleration of vibration decreases and then surges at the 8 times of the fBPF with the increasing of the wear-ring clearance.