scholarly journals Dynamic Characteristics of Rotating Stall in Mixed Flow Pump

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Xiaojun Li ◽  
Shouqi Yuan ◽  
Zhongyong Pan ◽  
Yi Li ◽  
Wei Liu
Keyword(s):  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Propagation Mechanism ◽  
Positive Slope ◽  
Mixed Flow ◽  
Outlet Flow ◽  
Research Gap ◽  
Flow Pump

Rotating stall, a phenomenon that causes flow instabilities and pressure hysteresis by propagating at some fraction of the impeller rotational speed, can occur in centrifugal impellers, mixed impellers, radial diffusers, or axial diffusers. Despite considerable efforts devoted to the study of rotating stall in pumps, the mechanics of this phenomenon are not sufficiently understood. The propagation mechanism and onset of rotating stall are not only affected by inlet flow but also by outlet flow as well as the pressure gradient in the flow passage. As such, the complexity of these concepts is not covered by the classical explanation. To bridge this research gap, the current study investigated prerotation generated at the upstream of the impeller, leakage flow at the tip clearance between the casing and the impeller, and strong reserve flow at the inlet of the diffuser. Understanding these areas will clarify the origin of the positive slope of the head-flow performance curve for a mixed flow pump. Nonuniform pressure distribution and adverse pressure gradient were also introduced to evaluate the onset and development of rotating stall within the diffuser.

Influence of tip leakage flow and inlet distortion flow on a mixed-flow pump with different tip clearances within the stall condition

2019 ◽  
Vol 234 (4) ◽  
pp. 433-453 ◽  
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi
Keyword(s):  
Internal Flow ◽  
Energy Performance ◽  
Rotating Stall ◽  
Design Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Mixed Flow ◽  
Tip Leakage ◽  
Flow Pump

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.

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

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.

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

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.

Suppression of Performance Curve Instability of a Mixed Flow Pump by Use of J-groove

2000 ◽  
Vol 122 (3) ◽  
pp. 592-597 ◽  
Author(s):  
Sankar L. Saha ◽  
Junichi Kurokawa ◽  
Jun Matsui ◽  
Hiroshi Imamura
Keyword(s):  
Angular Momentum ◽  
Pressure Gradient ◽  
Reverse Flow ◽  
Swirl Flow ◽  
Maximum Efficiency ◽  
Performance Curve ◽  
Positive Slope ◽  
Mixed Flow ◽  
Remarkable Effect ◽  
Flow Pump

In order to control and suppress performance curve instability characterized by the positive slope of head-capacity curve of a mixed flow pump, a very simple passive method utilizing shallow grooves mounted on a casing wall parallel to the pressure gradient (J-groove) is proposed. The optimum groove dimension and location for suppressing such an instability are determined experimentally. Results show that shallow grooves of adequate dimension and proper location can suppress such instability perfectly without decreasing the pump maximum efficiency. The remarkable effect of shallow grooves is to decrease both the swirl strength and the propagation of reverse flow at the impeller inlet region, through angular momentum absorption owing to mixing of groove reverse flow and swirl flow, yielding recovery of impeller theoretical head. [S0098-2202(00)02603-1]

Effect of Blade Thickness on Rotating Stall of Mixed-Flow Pump Using Entropy Generation Analysis

Energy ◽  
2021 ◽  
pp. 121381
Author(s):  
Leilei Ji ◽  
Wei Li ◽  
Weidong Shi ◽  
Fei Tian ◽  
Ramesh Agarwal
Keyword(s):  
Entropy Generation ◽  
Rotating Stall ◽  
Mixed Flow ◽  
Blade Thickness ◽  
Flow Pump

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

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.

scholarly journals Inlet and Outlet Flow of a Mixed-Flow Pump.

1992 ◽  
Vol 58 (549) ◽  
pp. 1479-1484 ◽  
Author(s):  
Jie JIANG ◽  
Junichi KUROKAWA
Keyword(s):  
Mixed Flow ◽  
Outlet Flow ◽  
Flow Pump

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

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.

Performance Study of a Mixed Flow Impeller Covering an Unsteady Flow Field

1992 ◽  
Vol 206 (2) ◽  
pp. 83-93 ◽  
Author(s):  
S Sarkar
Keyword(s):  
Axial Flow ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Performance Study ◽  
Mixed Flow ◽  
Pump Impeller ◽  
Wide Range ◽  
Reversal Flow ◽  
Flow Through ◽  
Flow Pump

The results presented here are part of a detailed programme measuring the aerodynamics of a high specific speed mixed flow pump impeller over a wide range of operating conditions, including its behaviour in the unsteady stalled regime. The aim is to elucidate the physics of the flow through such an impeller. The noticeable features are the formation of part-span rotating stall cells having no periodicity and organized structure at reduced flow and also the shifting positions of reversal flow pockets as the flowrate changes. Measurements of loss and its variation with span-wise positions and flowrates enable the variation of local efficiency to be determined. The overall flow picture is similar to that expected in an axial flow impeller, though the present impeller displays a narrow stall hysteresis loop almost right through its operating range.

scholarly journals Suppression of Mixed-Flow Pump Instability and Surge by the Active Alteration of Impeller Secondary Flows

1993 ◽  
Author(s):  
Akira Goto
Keyword(s):  
Flow Characteristic ◽  
Secondary Flows ◽  
Wake Flow ◽  
Streamwise Vorticity ◽  
Jet Injection ◽  
Positive Slope ◽  
Suction Surface ◽  
Mixed Flow ◽  
Pump System ◽  
Flow Pump

An active method for enhancing pump stability, featuring water jet injection at impeller inlet, was applied to a mixed-flow pump. The stall margin, between the design point and the positive slope region of the head-flow characteristic, was most effectively enlarged by injecting the jet in the counter-rotating direction of the impeller. The counter-rotating streamwise vorticity along the casing, generated by the velocity discontinuity due to the jet injection, altered the secondary flow pattern in the impeller by opposing the passage vortex and assisting the tip leakage vortex motion. The location of the wake flow was displaced away from the casing-suction surface corner of the impeller, thus avoiding the onset of the extensive corner separation, the cause of positive slope region of the head-flow characteristic. This method was also confirmed to be effective for stabilizing a pump system already in a state of surge.

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