Numerical investigation on the effects of leakage flow from Guide vane-clearance gaps in low specific speed Francis turbines

The rotor stator interaction in a low specific speed Francis model turbine and a pump-turbine is analyzed utilizing pressure sensors in the vaneless space and in the guide vane cascade. The measurements are analyzed relative to the runner angular position by utilizing an absolute encoder mounted on the shaft end. From the literature, the pressure in the analyzed area is known to be a combination of two effects: the rotating runner pressure and the throttling of the guide vane channels. The measured pressure is fitted to a mathematical pressure model to separate the two effects for two different runners. One turbine with 15+15 splitter blades and full-length blades and one pump-turbine with six blades are investigated. The blade loading on the two runners is different, giving different input for the pressure model. The main findings show that the pressure fluctuations in the guide vane cascade are mainly controlled by throttling for the low blade loading case and the rotating runner pressure for the higher blade loading case.

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Development of Low-Specific Speed New-Type Hydraulic Turbine Equipped with Volute: Numerical Investigation and Performance Prediction

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/774/1/012133 ◽

2021 ◽

Vol 774 (1) ◽

pp. 012133

Author(s):

T Irie ◽

W Takahashi ◽

K Miyagawa ◽

T Sugimoto ◽

T Naganuma ◽

...

Keyword(s):

Numerical Investigation ◽

Performance Prediction ◽

Hydraulic Turbine ◽

New Type ◽

Low Specific Speed ◽

Specific Speed ◽

And Performance

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Investigation of the Flow Instabilities of a Low Specific Speed Pump-Turbine: Part 1 — Experimental and Numerical Analysis

Volume 1: Fluid Applications and Systems; Fluid Measurement and Instrumentation ◽

10.1115/fedsm2020-20268 ◽

2020 ◽

Author(s):

Sabri Deniz ◽

Armando Del Rio ◽

Martin von Burg ◽

Manuel Tiefenthaler

Keyword(s):

Experimental Data ◽

Guide Vane ◽

Turbulence Models ◽

Operating Mode ◽

Rotating Stall ◽

Flow Instabilities ◽

Pump Turbine ◽

Flow Features ◽

Low Specific Speed ◽

Specific Speed

Abstract This is the first part of a two-part paper focusing on the flow instabilities of low-specific pump turbines. In this part, results of the CFD simulations and experiments of the research carried out on a low specific speed model pump-turbine at HSLU (Lucerne University of Applied Sciences) Switzerland are presented. The requirements of a stable and reliable pump-turbine operation under continuously expanding operating ranges, challenges the hydraulic design and requires new developments. Previous research at the HSLU [1] analyzed the instabilities of a medium specific speed (i.e. nq = 45) pump turbine. This paper presents the results of experimental (model pump-turbine at the test rig) and numerical (CFD) investigations of the pump-turbine instabilities of a low specific speed (nq = 25) pump-turbine in the turbine operating mode in the region of S-shaped characteristics (that is where the pump-turbine is synchronized and oscillations may occur during load rejection). The four-quadrant characteristics of a low specific speed model pump-turbine with two similar runners differentiating in the size (diameter) are measured. Testing of both runners with the same guide vane system provided information about the effects of the increased vaneless space (the distance between the guide vanes and runner) on the pump-turbine performance and stability both in turbine- and pump operating modes. A CFD methodology by using different numerical approaches and applying several turbulence models is developed in order to accurately predicting the characteristics of the reversible pump-turbines in the S-shaped region (speed no load conditions) as well as analyzing the flow features especially at off-design conditions. This CFD model is validated against the experimental data at 6° and 18° guide vane openings in turbine operating mode. With the measured data of the unsteady pressure measurements and detailed investigation of unstable ranges on the pump-turbine characteristics, flow instabilities in the low-specific speed model pump-turbine are analyzed. Relevant frequencies such as rotating stall, steady and unsteady vortex formations are determined. Based on the analysis of the experimental data and CFD results focusing especially on the flow features in the vaneless space and at the runner inlet, the onset and development of the flow instabilities are explored.

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Investigation of Interaction Between Tip Leakage Flow Generated by Unshrouded Impeller and Diffuser Internal Flow

Volume 3: Fluid Machinery; Erosion, Slurry, Sedimentation; Experimental, Multiscale, and Numerical Methods for Multiphase Flows; Gas-Liquid, Gas-Solid, and Liquid-Solid Flows; Performance of Multiphase Flow Systems; Micro/Nano-Fluidics ◽

10.1115/fedsm2018-83502 ◽

2018 ◽

Author(s):

Asuma Ichinose ◽

Norio Kimura ◽

Mamiko Yoshimura ◽

Tomoyuki Hayashi ◽

Kazuyoshi Miyagawa

Keyword(s):

Pressure Distribution ◽

Experimental Verification ◽

Cfd Simulation ◽

Internal Flow ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Impeller Blade ◽

Tip Leakage ◽

Low Specific Speed ◽

Specific Speed

Rocket turbo pumps and industrial pumps such as water feed pumps are required to work under high pressure conditions, therefore low specific speed pumps are needed in spite of high rotational speed. In recent years, unshrouded impellers were used because of easy manufacturing and cost reduction. However, when low specific speed unshrouded impellers are used in such conditions, complex tip leakage flow occur and decrease impeller performance. In addition, splitter blades are often used, the internal flow becomes even more complicated. Therefore, such the internal flow of the unshrouded impeller must be clarified. In this research, we have studied such a centrifugal pump, and we have analyzed the internal flow using experiments and CFD (Computational Fluid Dynamics) simulations. The experimental verification was carried out by measuring the total pressure distribution on the outlet of the impeller and the diffuser. The unsteady static pressure distribution at the shroud side of the impeller was measured to confirm pump performance. We used two types of CFD simulation to evaluate the internal flow in detail. In the first CFD simulation, the unsteady internal flow of an impeller was evaluated by carrying out DES (Detached Eddy Simulation) with a periodic boundary condition that does not contain the diffuser. In the second CFD simulation, interaction between the impeller leakage flow and the diffuser internal flow was evaluated by DES with the whole impeller and diffuser. From the experimental verification and CFD simulation, it was confirmed that a large-scale vortex structure caused by the tip leakage flow and the secondary flow was observed in the impeller blade-to-blade. And the influence of the impeller leakage flow on the diffuser internal flow and the diffuser performance was evaluated. From the above studies, it was confirmed that the tip leakage flow has a large influence on the impeller internal flow and the diffuser performance.

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Influence of Impeller Gap Drainage Width on the Performance of Low Specific Speed Centrifugal Pump

Journal of Marine Science and Engineering ◽

10.3390/jmse9020106 ◽

2021 ◽

Vol 9 (2) ◽

pp. 106

Author(s):

Yangyang Wei ◽

Yang Yang ◽

Ling Zhou ◽

Lei Jiang ◽

Weidong Shi ◽

...

Keyword(s):

High Pressure ◽

Numerical Calculation ◽

Flow Field ◽

Centrifugal Pump ◽

Low Pressure ◽

Slight Reduction ◽

Leakage Flow ◽

Low Specific Speed ◽

Specific Speed ◽

Gap Width

The centrifugal pump is one of the most important pieces of energy-consuming equipment in various hydraulic engineering applications. This paper takes a low specific speed centrifugal pump as the research object. Based on the research method combining numerical calculation and experimental verification, the influence of the gap drainage structure on the performance of the low specific speed centrifugal pump and its internal flow field distribution were investigated. The flow field inside the low specific speed centrifugal pump impeller under different gap widths was studied. The comparison between the numerical calculation results and the experimental results confirms that the numerical calculations in this paper have high accuracy. It was found that the gap drainage will reduce the head of the low specific speed centrifugal pump, but increase its hydraulic efficiency. Using a smaller gap width could greatly improve the performance of the low specific speed centrifugal pump on the basis of a slight reduction in the head. The high-pressure leakage flow at the gap flows from the blade pressure surface to the suction surface can effectively suppress the low-pressure area at the impeller inlet. The flow rate of the high-pressure leakage flow increases with the gap width. Excessive gap width may cause a low-pressure zone at the inlet of the previous flow passage. These results could serve as a reference for the subsequent gap design to further improve the operating stability of the low specific speed centrifugal pump.

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