Vortex Dynamics Analysis of Internal Flow Field of Mixed-Flow Pump under Alford Effect

Abstract

A multi-region dynamic slip method was established to study the internal flow characteristics of the mixed-flow pump under the Alford effect. The ANSYS Fluent software and the standard k-ε two-equation model were used to numerically predict the mixed-flow pump’s external characteristics and analyze the forces on the impeller and guide vane internal vortex structure and non-uniform tip gap of the mixed-flow pump at different eccentric distances. The research results show that the external characteristic results of the numerical calculation are consistent with the experimental measurement. The head error of the design flow operating point is about 5%, and the efficiency error is no more than 3%, indicating the high accuracy of numerical calculation. Eccentricity has a significant influence on the flow field in the tip area of the mixed-flow pump impeller, the distribution of vortex core in the impeller presents obvious asymmetry, the strength and distribution area of the vortex core in the small gap area of the tip increase obviously, which aggravates the flow instability and increases the energy loss. With the increase of eccentricity, the strength and number of vortex core structures in the guide vane also increase significantly, and obvious flow separation occurs near the inlet of the guide vane suction surface on the eccentric side of the impeller. The circumferential distribution of L1 and L2 values represents the friction pressure gap in the eccentric state, and the eccentricity has a more noticeable effect on L1 and L2 values at the small gap; With the increase of eccentricity, the values of vorticity moment components L1 and L2 increase, and the Alford moment on the impeller increases. The leading-edge region of the blade is the main part affected by the unstable torque of the flow field. With the increase of eccentricity, the impact degree of tip leakage flow deepens, and the change of the tip surface pressure is the most obvious. The impact area of tip leakage flow is mainly concentrated in the first half of the impeller channel, which has an impact on the blade inlet flow field but has little impact on the blade outlet flow field.

Analysis of Timing Effect on Flow Field and Pulsation in Vertical Axial Flow Pump

“…The flow fluctuation amplitude at the outlet of guide vane is 0.56% on average, and the flow distribution is relatively average. In order to clarify the variation of the internal vortex of the vertical axial flow pump in the timing effect, the regularized helicity was introduced to analyze the internal vortex of the impeller and guide vane of the vertical axial flow pump device in Reference [29]. Helicity is an important physical quantity to measure the topological structure of turbulent vorticity field [30].…”

Effects of guide vane angle on internal flows and vortex characteristic of reactor coolant pump passage under flow coastdown

“…Wang and Du et al [7] studied the Q criterion to capture the vortex structure, through the analysis of unsteady characteristics, it is found that the vortex structure in the impeller and guide vane channel will show periodic splitting, which will lead to the change of vortex structure at the inlet of guide vane and the blockage at the inlet. LI S [8] studied the variation of vorticity and distribution area of blade tip clearance of mixed-flow pump was observed by Q criterion. Ye et al [9] studied the quintic polynomial was used to fit the mathematical model of the flowrate and rotation speed of the RCP during idling, and the variation law of hydraulic parameters during idling was studied.…”

“…. Q criterion study the vortex dynamics characteristics in the reactor coolant pump idling, the second generation vortex identification method Q criterion was proposed by Hunt et al in 1988, which was obtained based on the eigenvalue of the velocity gradient tensor ▽V[8]. For incompressible fluid, the characteristic equation of ▽V explained by formula 1： 𝜆 3 + 𝑃𝜆 3 + 𝑄𝜆 + 𝑅 = 0…”

Influence of eccentric impeller on pressure pulsation of large-scale vaned-voluted centrifugal pump

“…29,30 Wang et al 31 found that the eccentric impeller has an obvious influences on the muti-stage centrifugal pump caused serious vibration. Zhao et al 32 found that the eccentricity influences radial force and cavitation in reactor coolant pump. Li et al 33 found that eccentricity has a significant influence on the strength, symmetry and distribution area of the vortex core in the small gap area of the tip increase obviously, which aggravates the flow instability and increases the energy loss.…”