Internal unsteady flow characteristics of centrifugal pump based on entropy generation rate and vibration energy

Abstract

The transient fluid exciting force induced by unsteady flow in the centrifugal pump is the only exciting force that cannot be effectively eliminated. In order to explore the vibration problem caused by unsteady flow in the centrifugal pump, the steady and unsteady numerical calculations of the internal flow in a centrifugal pump with low specific speed were carried out under different flow rate conditions. With volute circumferential pressure pulsation test, the accuracy of numerical calculations was verified. At the same time, the vibration acceleration sensors were arranged in different positions of the pump body to complete the vibration characteristics experiment under different working conditions. Based on the numerical results, the amount and location of the internal flow loss of the centrifugal pump were predicted by the entropy generation rate method. According to the results of the vibration test, the vibration energy distribution of the centrifugal pump under different working conditions was obtained. In combination with the entropy generation rate and vibration energy distribution, the change rules of flow loss and the vibration energy with the flow condition of the pump were analyzed. By using the frequency-domain analysis method, the pressure pulsation, the unsteady radial fluid exciting force fluctuation and the vibration acceleration were compared and analyzed to study the change rules of the pressure pulsation, the unsteady fluid exciting force and the vibration characteristics with the flow rate. The results show that the internal flow loss is mainly concentrated in the impeller runner near the volute tongue under low flow condition and the internal flow loss under large flow rate condition is mainly concentrated in the volute channel near the pump outlet. The vibration induced by the unsteady flow in the centrifugal pump is mainly low-frequency vibration, which is very sensitive to the change of the flow rate. The vibration energy in the middle- and high-frequency ranges is almost not affected by the working condition. The internal flow loss and the low-frequency vibration energy change with the flow condition, showing similar change rules.

Large Eddy Simulation of Periodic Transient Pressure Fluctuation in a Centrifugal Pump Impeller at Low Flow Rate

“…Zhao et al [7] analyzed the mechanism of pressure fluctuation and stall propagation caused by rotating stalls and found that flow separation occurred near the leading edge of the pressure surface and transformed into vortices along the channel. Jia [8] studied the transient fluid excitation force caused by the unsteady flow in a centrifugal pump and obtained that the internal flow loss and low-frequency vibration energy of the impeller varies with the flow conditions, showing similar changes. Ni [9] found that the coupling between the rotor-stator interaction and the collision of the fluid discharged from the diffuser with the circulating flow to the casing bottom is the main cause of the strong pressure pulsation.…”

Numerical investigation of energy loss in a centrifugal pump through kinetic energy dissipation theory

“…Most previous KED analyses for centrifugal pumps have focused on steady numerical results 15,16,18 and ignored the near-wall revised KED. 17,19,20 This study addresses these shortcomings. Energy loss is calculated by post-processing the 3D unsteady numerical results through KED theory, and the near-wall revised KED is considered.…”

Influence of Cutting Angle of Blade Trailing Edge on Unsteady Flow in a Centrifugal Pump Under Off-Design Conditions

“…Unstable flow structures, such as return vortex at the tongue, shedding vortex at the blade trailing edge and return vortex at the inlet or outlet, will occur in centrifugal pumps when they are operated under part-load conditions [4][5][6]. The rotor-stator interaction at the tongue and the shedding vortex at the blade trailing edge are the main causes of unstable pressure pulsation in centrifugal pumps [7,8]. The internal flow of centrifugal pumps is extremely complicated and is accompanied by a 3D transient unstable strong turbulent motion that is difficult to capture.…”