Numerical Simulation of the Tip Leakage Vortex Characteristics in a Semi-Open Centrifugal Pump

Abstract

Tip leakage vortex has an important influence on the performance of semi-open centrifugal pumps. Simulations based on the three-dimensional Reynolds-Averaged Navier–Stokes were conducted to study the structural characteristics of tip leakage vortex and its effects on the internal flow field, and the Shear Stress Transport k-ω turbulence model was used to simulate the whole flow passage of centrifugal pumps with tip clearances of 0 mm and 1 mm. Then, the tip leakage vortex was analyzed using the relative vorticity transport equation. The numerical data and experimental results agreed well. The leakage vortex formed in the tip clearance led to 18.7% and 14.4% decrease in head and efficiency under design condition, respectively, and the bigger the flow rate, the fast the performance decreased. Tip leakage vortex formed at the leading edge of the blade moved along the suction surface. Whereas the tip leakage vortex formed near the middle of the blade extended to the pressure surface of the adjacent blade. This phenomenon deteriorated the flow field and induced passage vortex, thereby reducing the static pressure and blade load and changing the static pressure distribution law. The formation and development of leakage vortex could be attributed to the relative vortex stretching the term. The Coriolis force term could reflect the change of vorticity caused by leakage flow, and the viscous diffusion term served as the vorticity source.

CFD-Rotordynamics Sequential Coupling Simulation Approach for the Flow-Induced Vibration of Rotor System in Centrifugal Pump

“…Flow rate Q des was taken as an example, under which the pressure fluctuations at five monitoring points in one impeller revolution were shown in Figure 16. Figure 16 shows the dominate pressure fluctuation period is 1/6 of the rotating period of the impeller, which agrees with the experimental regularity obtained by Wang et al [12]. However, pressure values and their amplitude variations are different for each monitoring point.…”

“…(node,t) = P(node)+P(node,t) (11) where the numerical value of P(node) is defined the arithmetic mean value of pressure in one revolution (12) where N is the number of time steps, t0 is the initial moment and ∆ is the time step length. Thus the value of P(node,t) is the difference between instantaneous pressure value (node,t) and P(node) P(node,t)=P(node,t)-P(node) (13) ̃( , ) is worth in-depth study as it indicates the instability of the inner flow of centrifugal pump.…”

“…Similar pulsation tendency is also fund in the hydraulic radial force on the impeller, because the hydraulic force mainly depends on the integration of pressure on the impeller surfaces. In addition, there are also other obvious frequency components rather than f BPF or multiple f n , which are stimulated by a serious complex unsteady flow behaviors, such as the jet-wake pattern along the blade extension direction, the flow impact on the tongue, and the flow separation on the blade suction surface [10][11][12]. The above behaviors usually become more evident under off-design conditions and would take much greater risks for the operation of centrifugal pump [13,14].…”

Transient characteristics of internal flow fields of mixed-flow pump with different tip clearances under stall condition

“…However, it creates a problem due to the presence of tip clearance between the blade rim and the impeller shroud, which causes very large pressure gradient along the blade rim and generates tip leakage flow (TLF) and tip leakage vortex (TLV) in the impeller flow channels. 5–7 When mixed-flow pump operates at the design flow rate, the TLF and TLV are stable and approximately account for 15% of the total energy losses in impeller 6 as shown by Liu et al. 7 Furthermore, it may also cause other performance problems as discussed later when the mixed-flow pump runs at flow rates different from design flow rate, especially near stall and stall condition.…”

“…5–7 When mixed-flow pump operates at the design flow rate, the TLF and TLV are stable and approximately account for 15% of the total energy losses in impeller 6 as shown by Liu et al. 7 Furthermore, it may also cause other performance problems as discussed later when the mixed-flow pump runs at flow rates different from design flow rate, especially near stall and stall condition. 8,9…”