Effect of the leakage flow in runner on flow characteristics of a Francis turbine model

Undesirable flow phenomena in Francis turbines are caused by pressure fluctuations induced under conditions of low flow rate; the resulting vortex ropes with precession in the draft tube (DT) can degrade performance and increase the instability of turbine operations. To suppress these DT flow instabilities, flow deflectors, grooves, or other structures are often added to the DT into which air or water is injected. This preliminary study investigates the effects of anti-cavity fins on the suppression of vortex ropes in DTs without air injection. Unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted using a scale-adaptive simulation shear stress transport turbulence model to observe the unsteady internal flow and pressure characteristics by applying anti-cavity fins in the DT of a Francis turbine model. A vortex rope with precession was observed in the DT under conditions of low flow rate, and the anti-cavity fins were confirmed to affect the mitigation of the vortex rope. Moreover, at the low flow rate conditions under which the vortex rope developed, the application of anti-cavity fins was confirmed to reduce the maximum unsteady pressure.

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Effect of Air Injection on the Internal Flow Characteristics in the Draft Tube of a Francis Turbine Model

Processes ◽

10.3390/pr9071182 ◽

2021 ◽

Vol 9 (7) ◽

pp. 1182

Author(s):

Seung-Jun Kim ◽

Yong Cho ◽

Jin-Hyuk Kim

Keyword(s):

Flow Rate ◽

Draft Tube ◽

Pressure Fluctuations ◽

Flow Characteristics ◽

Internal Flow ◽

Air Injection ◽

Low Flow ◽

Francis Turbine ◽

Navier Stokes ◽

Vortex Rope

Under low flow-rate conditions, a Francis turbine exhibits precession of a vortex rope with pressure fluctuations in the draft tube. These undesirable flow phenomena can lead to deterioration of the turbine performance as manifested by torque and power output fluctuations. In order to suppress the rope with precession and a swirl component in the tube, the use of anti-swirl fins was investigated in a previous study. However, vortex rope generation still occurred near the cone of the tube. In this study, unsteady-state Reynolds-averaged Navier–Stokes analyses were conducted with a scale-adaptive simulation shear stress transport turbulence model. This model was used to observe the effects of the injection in the draft tube on the unsteady internal flow and pressure phenomena considering both active and passive suppression methods. The air injection affected the generation and suppression of the vortex rope and swirl component depending on the flow rate of the air. In addition, an injection level of 0.5%Q led to a reduction in the maximum unsteady pressure characteristics.

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Flow characteristics and influence associated with inter-blade cavitation vortices at deep part load operations of a Francis turbine

Journal of Physics Conference Series ◽

10.1088/1742-6596/813/1/012029 ◽

2017 ◽

Vol 813 ◽

pp. 012029 ◽

Cited By ~ 2

Author(s):

K. Yamamoto ◽

A. Müller ◽

A. Favrel ◽

C. Landry ◽

F. Avellan

Keyword(s):

Flow Characteristics ◽

Francis Turbine ◽

Deep Part ◽

Part Load

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Fluid Force Moment on the Backshroud of a Francis Turbine Runner in Precession Motion

Journal of Fluids Engineering ◽

10.1115/1.4001618 ◽

2010 ◽

Vol 132 (5) ◽

Cited By ~ 2

Author(s):

Bingwei Song ◽

Hironori Horiguchi ◽

Yumeto Nishiyama ◽

Shinichiro Hata ◽

Zhenyue Ma ◽

...

Keyword(s):

Flow Model ◽

Swirl Flow ◽

Francis Turbine ◽

Leakage Flow ◽

Fluid Force ◽

Disk Rotation ◽

Leakage Flow Rate ◽

Turbine Runner ◽

Force Moment ◽

Axial Clearance

The fundamental characteristics of rotordynamic fluid force moment on the backshroud of a Francis turbine runner in precession motion were studied using model tests and computations based on a bulk flow model. The runner is modeled by a disk positioned close to a casing with a small axial clearance. An inward leakage flow is produced by an external pump in the model test. The effects of the leakage flow rate, the preswirl velocity at the inlet of the clearance, and the axial clearance on the fluid force moment were examined. It was found that the fluid force moment encourages the precession motion at small forward precession angular velocity ratios and the region encouraging the precession motion is affected by the preswirl velocity. Through the comparisons of the fluid force moment with and without the rotation of the disk, it was found that the normal moment without the disk rotation did not have the effect to encourage the precession motion. Thus, the swirl flow due to disk rotation was found to be responsible for the encouragement of the precession motion.

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Experimental and Numerical Study of Honeycomb Tip on Suppressing Tip Leakage Flow in Turbine Cascade

Volume 2A: Turbomachinery ◽

10.1115/gt2017-64942 ◽

2017 ◽

Cited By ~ 4

Author(s):

Yunfeng Fu ◽

Fu Chen ◽

Huaping Liu ◽

Yanping Song

Keyword(s):

Numerical Study ◽

Flow Characteristics ◽

Leakage Flow ◽

Exit Section ◽

Turbine Cascade ◽

Tip Leakage Flow ◽

Physical Processes ◽

Tip Leakage ◽

Gap Height ◽

Positive Effect

In this paper, the effect of a novel honeycomb tip on suppressing tip leakage flow in a highly-loaded turbine cascade has been experimentally and numerically studied. The research focuses on the mechanisms of honeycomb tip on suppressing tip leakage flow and affecting the secondary flow in the cascade, as well as the influences of different clearance heights on leakage flow characteristics. In addition, two kinds of local honeycomb tip structures are pro-posed to explore the positive effect on suppressing leakage flow in simpler tip honeycomb structures. Based on the experimental and numerical results, the physical processes of tip leakage flow and its interaction with main flow are analyzed, the following conclusions can be obtained. Honeycomb tip rolls up a number of small vortices and radial jets in regular hexagonal honeycomb cavities, increasing the flow resistance in the clearance and reducing the velocity of leakage flow. As a result, the structure of honeycomb tip not only suppresses the leakage flow effectively, but also has positive effect on reducing the associated losses in cascade by reducing the strength of leakage vortex. Compare to the flat tip cascade at 1%H gap height, the relative leakage flow in honeycomb tip cascade reduces from 3.05% to 2.73%, and the loss at exit section is also decreased by 10.63%. With the increase of the gap height, the tip leakage flow and loss have variations of direct proportion with it, but their growth rates in the honeycomb tip cascade are smaller. Consider the abradable property of the honeycomb seal, a smaller gap height is allowed in the cascade with honeycomb tip, and that means honeycomb tip has better effect on suppressing leakage flow. Two various local honeycomb tip structures has also been discussed. It shows that local raised honeycomb tip has better suppressing leakage flow effect than honeycomb tip, while local concave honeycomb tip has no more effect than honeycomb tip. Compare to flat tip cascade, the leakage flow in honeycomb tip cascade, local concave tip cascade and local raised honeycomb tip cascade decrease by nearly 17.33%, 15.51% and 30.86% respectively, the losses at exit section is reduced by 13.38%, 12% and 28.17% respectively.

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Comparison of Turbine Tip Leakage Flow for Flat Tip and Squealer Tip Geometries at High-Speed Conditions

Journal of Turbomachinery ◽

10.1115/1.2162183 ◽

2004 ◽

Vol 128 (2) ◽

pp. 213-220 ◽

Cited By ~ 82

Author(s):

Nicole L. Key ◽

Tony Arts

Keyword(s):

Reynolds Number ◽

High Speed ◽

Flow Characteristics ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage ◽

Cascade Arrangement ◽

Oil Flow ◽

Blade Tip ◽

Tip Velocity

The tip leakage flow characteristics for flat and squealer turbine tip geometries are studied in the von Karman Institute Isentropic Light Piston Compression Tube facility, CT-2, at different Reynolds and Mach number conditions for a fixed value of the tip gap in a nonrotating, linear cascade arrangement. To the best knowledge of the authors, these are among the very few high-speed tip flow data for the flat tip and squealer tip geometries. Oil flow visualizations and static pressure measurements on the blade tip, blade surface, and corresponding endwall provide insight to the structure of the two different tip flows. Aerodynamic losses are measured for the different tip arrangements, also. The squealer tip provides a significant decrease in velocity through the tip gap with respect to the flat tip blade. For the flat tip, an increase in Reynolds number causes an increase in tip velocity levels, but the squealer tip is relatively insensitive to changes in Reynolds number.

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Inter-Blade Vortex Characteristics With the Blockage Effects of Runner Blade in a Francis Hydro Turbine Model

Volume 3B: Fluid Applications and Systems ◽

10.1115/ajkfluids2019-4805 ◽

2019 ◽

Author(s):

Seung-Jun Kim ◽

Jin-Hyuk Kim ◽

Young-Seok Choi ◽

Yong Cho ◽

Jong-Woong Choi

Keyword(s):

Flow Rate ◽

Flow Characteristics ◽

Internal Flow ◽

Operating Conditions ◽

Low Flow ◽

Hydro Turbine ◽

Runner Blade ◽

Performance Reduction ◽

Turbine Model ◽

Low Flow Rate

Abstract This study presents the numerical analysis on the inter-blade vortex characteristics along with the blockage effects of runner blade in a Francis hydro turbine model with various flow rate conditions. The turbine model showed different flow characteristics in the runner blade passages according to operating conditions, and inter-blade vortex was observed at lower flow rate conditions. This inter-blade vortex can lead to performance reduction, vibration, and instability for smooth operation of turbine systems. The previous study on blockage effects on various runner blade thickness, showed its influence on hydraulic performance and internal flow characteristics at low flow rate conditions. Therefore, the inter-blade vortex characteristics can be altered with the blockage effects at low flow rate conditions in a Francis hydro-turbine. For investigating the internal flow and unsteady pressure characteristics, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes calculations are performed. These inter-blade vortices were captured at the leading and trailing edges close to the runner hub. These vortex regions showed flow separation and stagnation flow while blockage effects contributed for decreasing the inter-blade vortex at low flow rate conditions.

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Experimental and Numerical Analysis on Flow Characteristics in a Double Helix Screw Pump

Energies ◽

10.3390/en12183420 ◽

2019 ◽

Vol 12 (18) ◽

pp. 3420 ◽

Cited By ~ 1

Author(s):

Weibin Zhang ◽

Qifeng Jiang ◽

Gérard Bois ◽

Hong Li ◽

Xiaobing Liu ◽

...

Keyword(s):

Numerical Analysis ◽

Double Helix ◽

Flow Characteristics ◽

Leakage Flow ◽

Inlet Section ◽

Screw Pump ◽

Local Flow ◽

Local Distortion ◽

Urans Cfd ◽

Pump Inlet

Experimental overall performances on a double helix screw pump are presented and discussed, focusing on the leakage flow for two different rotational speeds. A comparison between experimental and URANS CFD approaches is performed in order to check the CFD closure models’ validity. Some specific local flow characteristics are extracted from the numerical results which give explanations about leakage backflows inside the screws and local distortion at the pump inlet section.

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Numerical analysis of the groove effect on the tip leakage vortex cavitating flow

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

10.1177/0957650919884192 ◽

2019 ◽

Vol 234 (6) ◽

pp. 836-847

Author(s):

Zhaodan Fei ◽

Rui Zhang ◽

Hui Xu ◽

Tong Mu

Keyword(s):

Flow Pattern ◽

Flow Characteristics ◽

Cavitating Flow ◽

Main Flow ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage Vortex ◽

Tip Leakage ◽

Curvature Effects ◽

The Mean

In this paper, the groove effect on the tip leakage vortex cavitating flow characteristics of a simplified NACA0009 hydrofoil with tip gap is studied. Considering local rotation characteristics and curvature effects of the tip leakage vortex flow, the rotation-curvature corrected shear-stress-transport turbulence model is applied to simulate the time-averaged turbulent flow. The Zwart–Gerber–Belamri cavitation model is used to simulate the cavitating flow. The results show that the groove could affect the tip leakage vortex cavitating flow. The groove enhances the interaction between the tip leakage flow and main flow, and then it affects the cavitation of the tip leakage vortex. Compared with the non-groove case, for groove cases of αgre ≤75°, the tip leakage vortex cavitating flow is suppressed, the flow pattern in the gap is improved, and the mean leakage velocity Vlk < 0.8. The region of high leakage velocity is eliminated and the distribution of the pressure is more uniform. The tip leakage vortex cavitation area is reduced, and the maximum decrease is 72.90%. While for groove cases of αgre≥90°, neither the tip leakage vortex cavitating flow nor flow pattern in the tip gap is ameliorated, the mean leakage velocity Vlk lies the range from 0.90 to 0.96. The region of high leakage velocity still exists and even the tip leakage vortex cavitation area is increased. Based on three-dimensional streamlines and vorticity transport equation, the interaction between the tip leakage flow and main flow leads to the variation of the tip leakage vortex cavitating flow. This paper aims for a useful reference to mitigate the tip leakage vortex cavitation and control the influence of the tip leakage vortex cavitating flow for the hydraulic machinery.

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