Energy Performance and Flow Patterns of a Mixed-Flow Pump with Different Tip Clearance Sizes

In order to investigate the effect of impeller tip clearance on internal flow fields and the rotating stall inception impacted by tip leakage vortex and inlet unsteady flow in a mixed-flow pump, mixed-flow pump models with tip clearances of 0.5 mm, 0.8 mm, and 1.1 mm were numerically calculated, and then the energy performance curves and internal flow structures were obtained and compared. The results show that the pump efficiency and the internal flow fields of numerical calculation are in good agreement with experimental results at design flow rate and near-stall condition. A portion of the positive slope segment appears in the energy performance curves under different tip clearances. The lowest head of the mixed-flow pump in the positive slope region decreases with the increase of the tip clearance while the highest head shows an opposite situation indicating that mixed-flow pumps are easier to stall under small tip clearance. At the design flow rate condition, the tip leakage vortex is relatively stable under different tip clearances and appears as a “snail shell” shape, whereas in rotating stall conditions, the “snail shell” shape disappear and the tip leakage flow on blade front forms a “flat” vortex structure. The inlet swirl flow not only affects the tip leakage flow in rotating stall conditions under different tip clearances, but also blocks the fluid from the inlet pipe. Under the circumstance of the same tip clearance, the main frequency amplitude of pressure pulsation coefficient gradually shifts away from blade passing frequency (96.67 Hz) to the axial frequency (24.17 Hz) when the pump operates in the stall condition.

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Effect of Tip Clearance on Rotating Stall in a Mixed-Flow Pump

Volume 2C: Turbomachinery ◽

10.1115/gt2019-90134 ◽

2019 ◽

Author(s):

Wei Li ◽

Ramesh K. Agarwal ◽

Ling Zhou ◽

Enda Li ◽

Leilei Ji

Keyword(s):

Flow Separation ◽

Internal Flow ◽

Energy Performance ◽

Rotating Stall ◽

Tip Clearance ◽

Leakage Flow ◽

Pump Efficiency ◽

Mixed Flow ◽

Performance Curves ◽

Flow Pump

Abstract The non-uniform disturbance in the circumferential direction is the main cause for the occurrence of rotating stall in turbomachinery. In order to study the effect of tip clearance leakage flow on rotating stall, the mixed-flow pump models with different tip clearances are numerically simulated, and then the energy performance curves and internal flow structures are obtained and compared. The results show that the computed pump efficiency and the internal flow field of the pump from numerical simulation are in good agreement with the experimental results. A saddle region appears in the energy performance curves of the three tip clearances, and with decrease in tip clearance, the head and efficiency of the mixed-flow pump increase and the critical stall point shifts, and the stable operating range of the mixed-flow pump decreases, which indicates that the mixed-flow pump stalls easily for smaller tip clearance. Under the deep stall condition, the influence of the leakage flow in the end wall area increases gradually with decrease in clearance. For small clearance, the leakage flow moves away from the suction surface to some distance to form a number of leakage vortex strips with the mainstream flow and flows over the leading edge of the next blade and then flows downstream into different flow passages, generating backflow and secondary flow separation at the blade inlet, which seriously damages the spatial structure of the inlet flow. This results in the earlier occurrence of stall. With increase in clearance, the leakage vortex develops along the radial direction towards the middle of the flow channel and large flow separation occurs in the downstream channel, which induces deep stall. For 0.8mm clearance, the whole impeller outlet passage is almost blocked by the backflow of the guide vane inlet, and a deep stall is induced.

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Effect of Tip Clearance on Rotating Stall in A Mixed-Flow Pump

Journal of Turbomachinery ◽

10.1115/1.4050625 ◽

2021 ◽

pp. 1-39

Author(s):

Wei Li ◽

Leilei Ji ◽

Enda Li ◽

Ling Zhou ◽

Ramesh Agarwal

Keyword(s):

Flow Separation ◽

Internal Flow ◽

Energy Performance ◽

Rotating Stall ◽

Tip Clearance ◽

Leakage Flow ◽

Pump Efficiency ◽

Mixed Flow ◽

Performance Curves ◽

Flow Pump

Abstract The non-uniform disturbance in circumferential direction is main cause for occurrence of rotating stall in turbomachinery. In order to study the effect of tip clearance leakage flow on rotating stall, mixed-flow pump models with different tip clearances are simulated and energy performance curves and internal flow structures are obtained and compared. The results show that the computed pump efficiency and the internal flow field of the pump are in good agreement with experimental results. A saddle region appears in energy performance curves of three tip clearances and with decrease in tip clearance, the head and efficiency of mixed-flow pump increase and critical stall point shifts and stable operating range of mixed-flow pump decreases, which indicates that mixed-flow pump stalls easily for smaller tip clearance. Under deep stall condition, influence of leakage flow in end wall area increases gradually with decrease in clearance. For small clearance, the leakage flow moves away from suction surface to some distance to form number of leakage vortex strips with mainstream flow and flows over the leading edge of next blade and then flows downstream into different flow passages generating back flow and secondary flow separation at the blade inlet, which seriously damages the spatial structure of inlet flow. This results in earlier occurrence of stall. With increase in clearance, the leakage vortex develops along radial direction towards middle of flow channel and large flow separation occurs in downstream channel which induces deep stall.

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Experimental Study of Pressure Pulsation in a Mixed-Flow Pump with Different Tip Clearances Based on Wavelet Analysis

Shock and Vibration ◽

10.1155/2020/9041686 ◽

2020 ◽

Vol 2020 ◽

pp. 1-15

Author(s):

Leilei Ji ◽

Wei Li ◽

Weidong Shi ◽

Ling Zhou ◽

Ramesh Agarwal

Keyword(s):

Performance Test ◽

Pressure Pulsation ◽

Rotation Period ◽

Low Frequency ◽

Energy Performance ◽

Tip Clearance ◽

Wavelet Coherence ◽

Energy Concentration ◽

Mixed Flow ◽

Flow Pump

In order to investigate the effect of various impeller tip clearances on the pressure pulsation in a mixed-flow pump, the energy performance test and pressure pulsation experiment of a mixed-flow pump with different tip clearances are studied simultaneously. The pressure pulsation signals at impeller inlet, middle, and oulet are processed and analyzed by the wavelet transform. The results show that the change of tip clearance can affect the head and efficiency of mixed-flow pump. Under designed flow rate, when the tip clearance increases from 0.2 mm to 1.1 mm, the head and efficiency decrease by 18.1% and 11.6%, respectively. Due to the strong influence of blade passing frequency (BPF) at impeller middle, the period of pressure pulsation curve is about 1/4 of impeller rotation period. At impeller inlet, the low-frequency pulsation with energy concentration is the main disturbance frequency, and, with the increase of tip clearance, not only does the high-value region of wavelet spectrum expand to low-frequency direction but also it is easy to form second-order peaks in the time-averaged wavelet curve. At impeller outlet, affected by BPF and rotor-stator interaction (RSI), the high-frequency disturbance in RSI area decreases first and then increases. The wavelet coherence demonstrates the stable low-frequency disturbances in comparison to others and it will affect the flow field at impeller middle.

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Effect of Tip Clearance on Suction Performance at Different Flow Rates in a Mixed Flow Pump

Volume 1B, Symposia: Fluid Machinery; Fluid-Structure Interaction and Flow-Induced Noise in Industrial Applications; Flow Applications in Aerospace; Flow Manipulation and Active Control: Theory, Experiments and Implementation; Multiscale Methods for Multiphase Flow; Noninvasive Measurements in Single and Multiphase Flows ◽

10.1115/fedsm2014-21207 ◽

2014 ◽

Author(s):

Yo Han Jung ◽

Young Uk Min ◽

Jin Young Kim

Keyword(s):

Performance Test ◽

Stokes Equations ◽

Flow Characteristics ◽

Tip Clearance ◽

Low Flow ◽

Tip Leakage Flow ◽

Mixed Flow ◽

Flow Rates ◽

Suction Performance ◽

Flow Pump

This paper presents a numerical investigation of the effect of tip clearance on the suction performance and flow characteristics at different flow rates in a vertical mixed-flow pump. Numerical analyses were carried out by solving three-dimensional Reynolds-averaged Navier-Stokes equations. Steady computations were performed for three different tip clearances under noncavitating and cavitating conditions at design and off-design conditions. The pump performance test was performed for the mixed-flow pump and numerical results were validated by comparing the experimental data for a system characterized by the original tip clearance. It was shown that for large tip clearance, the head breakdown occurred earlier at the design and high flow rates. However, the head breakdown was quite delayed at low flow rate. This resulted from the cavitation structure caused by the tip leakage flow at different flow rates.

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

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650920962250 ◽

2020 ◽

pp. 095765092096225

Author(s):

Leilei Ji ◽

Wei Li ◽

Weidong Shi ◽

Ramesh Agarwal

Keyword(s):

Swirling Flow ◽

Internal Flow ◽

Flow Fields ◽

Design Flow ◽

Tip Clearance ◽

Tip Leakage Flow ◽

Mixed Flow ◽

Transient Characteristics ◽

Initial Starting ◽

Flow Pump

This paper investigates the influence of different tip clearances on the transient characteristics of mixed-flow pump under stall condition. The instantaneous internal flow fields of mixed-flow pump with four tip clearances (0.2 mm, 0.5 mm, 0.8 mm and 1.1 mm) are explored by conducting unsteady time accurate simulations. Reynolds-averaged Navier-Stokes (RANS) equations are employed in the simulations and the results of computations are compared with experimental data. The results show that the pump head decreases by 22.1% and the pump efficiency drops by 13.9% at design flow condition when the impeller tip clearance increases from 0.2 mm to 1.1 mm. The swirling flow occurs in the inlet pipe of the mixed-flow pump with different tip clearances under stall condition, and the initial starting point of the swirling flow gets further away from the impeller inlet with increase in tip clearance because of increase in circumferential velocity and change in momentum of the tip leakage flow (TLF). The high turbulent eddy dissipation (TED) regions in the flow are attributed to the TLF, swirling flow, back flow and stall vortex, and their intensity are affected by the change in tip clearance. The oscillating trend of time domain distribution of TED enhances first and then decreases with increase in tip clearance and it exhibits a propagation feature under the effect of stall vortex, while most of the energy in the frequency domain remains concentrated in the low frequency part under stall condition.

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Performance of a Mixed Flow Pump with Varying Tip Clearance: Part 2

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/pime_proc_1996_210_050_02 ◽

1996 ◽

Vol 210 (4) ◽

pp. 319-327 ◽

Cited By ~ 7

Author(s):

S Soundranayagam ◽

T K Saha

Keyword(s):

Close Agreement ◽

Tip Clearance ◽

Pump Efficiency ◽

Centrifugal Pumps ◽

Mixed Flow ◽

Loss Distribution ◽

Specific Speed ◽

Flow Pump ◽

Relative Flow

Measurements in a mixed flow pump of non-dimensional specific speed k = 1.89 [ NS = 100 r/min (metric)] are analysed to give loss distribution and local hydraulic efficiencies at different flowrates and values of tip clearance. Fairly close agreement is obtained between the relative flow angles leaving the blading as predicted by simple deviation and slip models and derived from the measurements. The head developed is broken up into two parts: that contributed by Coriolis action and that associated with blade circulation. It is suggested that lift coefficients based on blade circulation are of limited value in selecting blade profiles. The variation of pump efficiency with tip clearance is greater than that reported for centrifugal pumps.

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Spatial–Temporal Evolution of Tip Leakage Vortex in a Mixed-Flow Pump With Tip Clearance

Journal of Fluids Engineering ◽

10.1115/1.4042756 ◽

2019 ◽

Vol 141 (8) ◽

Cited By ~ 48

Author(s):

Yabin Liu ◽

Lei Tan

Keyword(s):

Temporal Evolution ◽

Flow Instability ◽

Dominant Frequency ◽

Oscillation Period ◽

Relative Vorticity ◽

Tip Clearance ◽

Mixed Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Flow Pump

Tip clearance in pump induces tip leakage vortex (TLV), which interacts with the main flow and leads to instability of flow pattern and decrease of pump performance. In this work, the characteristics of TLV in a mixed-flow pump are investigated by the numerical simulation using shear stress transport (SST) k–ω turbulence model with experimental validation. The trajectory of the primary tip leakage vortex (PTLV) is determined, and a power function law is proposed to describe the intensity of the PTLV core along the trajectory. Spatial–temporal evolution of the TLV in an impeller revolution period T can be classified into three stages: splitting stage, developing stage, and merging stage. The TLV oscillation period TT is found as 19/160 T, corresponding to the frequency 8.4 fi (fi is impeller rotating frequency). Results reveal that the TLV oscillation is intensified by the sudden pressure variation at the junction of two adjacent blades. On analysis of the relative vorticity transport equation, it is revealed that the relative vortex stretching item in Z direction is the major source of the splitting and shedding of the PTLV. The dominant frequency of pressure and vorticity fluctuations on the PTLV trajectory is 8.4 fi, same as the TLV oscillation frequency. This result reveals that the flow instability in the PTLV trajectory is dominated by the oscillation of the TLV. The blade number has significant effect on pressure fluctuation in tip clearance and on blade pressure side, because the TLV oscillation period varies with the circumferential length of flow passage.

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