Performance prediction and flow analysis in the vaned distributor of a pump turbine under low flow rate in pump mode

Pump-turbines are often used to provide a stable power supply with a constant frequency in response to intermittent renewable energy resources. However, existing pumped-storage power stations often operate under off-design conditions because of the increasing amounts of inconsistent renewable resources that have been added to the grid. Under off-design low flow rate conditions, inter-blade vortex and vortex rope phenomena usually develop in the runner and draft tube passages, respectively, in turbine mode. These vortices cause complicated flow patterns and pressure fluctuations that destabilize the operation of the pump-turbine system. Therefore, this study investigates the influence of correlation between the inter-blade vortex and vortex rope phenomena under low flow rate conditions. Three-dimensional steady- and unsteady-state Reynolds-averaged Navier–Stokes equations were calculated with a two-phase flow analysis using a shear stress transport as the turbulence model. The inter-blade vortices in the runner passages were captured well at the low flow rate conditions, and the vortex rope was found to develop within a specific range of low flow rates. These vortex regions showed a blockage effect and complicated flow characteristics with backflow in the passages. Moreover, higher unsteady pressure characteristics occurred at locations where the vortices were especially pronounced.

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Impact of guide vane opening angle on the flow stability in a pump-turbine in pump mode

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406216635204 ◽

2016 ◽

Vol 231 (13) ◽

pp. 2484-2492 ◽

Cited By ~ 6

Author(s):

Di Zhu ◽

Ruofu Xiao ◽

Ran Tao ◽

Weichao Liu

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Flow Regime ◽

Flow Rate ◽

Guide Vane ◽

Low Flow ◽

Opening Angle ◽

Pump Mode ◽

Pump Turbine ◽

Hydraulic Losses

In the pump mode (storage mode) of a pump-turbine, unstable head variations occur as the flow rate decreases, leading to unstable, unsafe operation. Thus, the hydrodynamics of pump-turbines in the unstable operating range should be investigated to improve their designs. This study presents experimental and numerical studies of the hydrodynamics. The experiments investigated the external characteristics with the head instabilities captured by both the model tests and the computational fluid dynamics simulations. The computational fluid dynamics model used detached eddy simulations to study the flow details which showed that hydraulic losses were the reason for the unstable head variations and the poor flow regime was the source of the losses. In the unstable, low flow rate range, the flow direction is no longer consistent with the guide vane direction, so undesirable flow structures develop in the passages. Therefore, appropriate guide vane opening angles are needed to improve the flow regime and reduce the hydraulic losses. These will enhance the operating stability and safety in engineering applications.

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Optimized Blade Design of Counter-Rotating-Type Pump-Turbine Unit Operating in Pump and Turbine Modes

International Journal of Rotating Machinery ◽

10.1155/2018/6069780 ◽

2018 ◽

Vol 2018 ◽

pp. 1-12

Author(s):

Jin-Woo Kim ◽

Jun-Won Suh ◽

Young-Seok Choi ◽

Kyoung-Yong Lee ◽

Toshiaki Kanemoto ◽

...

Keyword(s):

Flow Rate ◽

Turbine Unit ◽

Stokes Equations ◽

Flow Analysis ◽

Three Dimensional ◽

Latin Hypercube Sampling ◽

Low Flow ◽

Pump Turbine ◽

Design Variables ◽

Turbine Mode

In this study, a counter-rotating-type pump-turbine unit was optimized to improve the pump and turbine mode efficiencies simultaneously. Numerical analysis was carried out by solving three-dimensional Reynolds-averaged Navier–Stokes equations using the shear stress turbulence model. The hub and tip blade angles of the rear impeller (in the pump mode) were selected as the design variables by conducting a sensitivity test. An optimization process based on steady flow analysis was conducted using a radial basis neural network surrogate model with Latin hypercube sampling. The pump and turbine mode efficiencies of the unit were selected as the objective functions and they combined into a single specific objective function with the weighting factors. Consequently, the pump and turbine mode efficiencies of the optimum design increased simultaneously at overall range of flow rate, except for low flow rate of turbine mode, compared to the reference design.

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The performance of a high head reversible pump-turbine (1st report, Effect of impeller characteristics on the pump performance in low flow rate range)

TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series B ◽

10.1299/kikaib.50.459_2795 ◽

1984 ◽

Vol 50 (459) ◽

pp. 2795-2799 ◽

Cited By ~ 1

Author(s):

Takeo TAKAGI ◽

Toshiaki YOKOYAMA ◽

Kazuo NIIKURA

Keyword(s):

Flow Rate ◽

Low Flow ◽

Pump Turbine ◽

Pump Performance ◽

Rate Range ◽

Flow Rate Range ◽

High Head ◽

Low Flow Rate

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Backflow effects on mass flow gain factor in a centrifugal pump

Science Progress ◽

10.1177/0036850421998865 ◽

2021 ◽

Vol 104 (2) ◽

pp. 003685042199886

Author(s):

Wenzhe Kang ◽

Lingjiu Zhou ◽

Dianhai Liu ◽

Zhengwei Wang

Keyword(s):

Centrifugal Pump ◽

Mass Flow ◽

Flow Rate ◽

Low Frequency ◽

Gain Factor ◽

Low Flow ◽

Cavity Volume ◽

Cavitating Flows ◽

Inlet Tube ◽

Low Flow Rate

Previous researches has shown that inlet backflow may occur in a centrifugal pump when running at low-flow-rate conditions and have nonnegligible effects on cavitation behaviors (e.g. mass flow gain factor) and cavitation stability (e.g. cavitation surge). To analyze the influences of backflow in impeller inlet, comparative studies of cavitating flows are carried out for two typical centrifugal pumps. A series of computational fluid dynamics (CFD) simulations were carried out for the cavitating flows in two pumps, based on the RANS (Reynolds-Averaged Naiver-Stokes) solver with the turbulence model of k- ω shear stress transport and homogeneous multiphase model. The cavity volume in Pump A (with less reversed flow in impeller inlet) decreases with the decreasing of flow rate, while the cavity volume in Pump B (with obvious inlet backflow) reach the minimum values at δ = 0.1285 and then increase as the flow rate decreases. For Pump A, the mass flow gain factors are negative and the absolute values increase with the decrease of cavitation number for all calculation conditions. For Pump B, the mass flow gain factors are negative for most conditions but positive for some conditions with low flow rate coefficients and low cavitation numbers, reaching the minimum value at condition of σ = 0.151 for most cases. The development of backflow in impeller inlet is found to be the essential reason for the great differences. For Pump B, the strong shearing between backflow and main flow lead to the cavitation in inlet tube. The cavity volume in the impeller decreases while that in the inlet tube increases with the decreasing of flow rate, which make the total cavity volume reaches the minimum value at δ = 0.1285 and then the mass flow gain factor become positive. Through the transient calculations for cavitating flows in two pumps, low-frequency fluctuations of pressure and flow rate are found in Pump B at some off-designed conditions (e.g. δ = 0.107, σ = 0.195). The relations among inlet pressure, inlet flow rate, cavity volume, and backflow are analyzed in detail to understand the periodic evolution of low-frequency fluctuations. Backflow is found to be the main reason which cause the positive value of mass flow gain factor at low-flow-rate conditions. Through the transient simulations of cavitating flow, backflow is considered as an important aspect closely related to the hydraulic stability of cavitating pumping system.

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A Meanline Model for Impeller Flow Recirculation

Volume 6: Turbomachinery, Parts A, B, and C ◽

10.1115/gt2008-51349 ◽

2008 ◽

Cited By ~ 10

Author(s):

Xuwen Qiu ◽

David Japikse ◽

Mark Anderson

Keyword(s):

Flow Rate ◽

Recirculation Zone ◽

Reverse Flow ◽

Low Flow ◽

Suction Surface ◽

Blade Loading ◽

Flow Recirculation ◽

Impeller Outlet ◽

Active Flow ◽

Low Flow Rate

Flow recirculation at the impeller inlet and outlet is an important feature that affects impeller performance, especially the power consumption at a very low flow rate. Although the mechanisms for this flow phenomenon have been studied, a practical model is needed for meanline modeling of impeller off-design performance. In this paper, a meanline recirculation model is proposed. At the inlet, the recirculation zone acts as area blockage to relieve the large incidence of the active flow at a low flow rate. The size of the blockage is estimated through a critical area ratio of an artificial “inlet diffuser” from the inlet to throat. The intensity of the reverse flow can then be calculated by assuming a linear velocity profile of meridional velocity in the recirculation zone. At the impeller outlet, a recirculation zone near the suction surface is established to balance the velocity difference on the pressure and suction sides of the blade. The size and the intensity of the outlet recirculation zone is assumed related to blade loading, which can be evaluated based on flow turning and Coriolis force. A few validation cases are presented showing a good comparison between test data and prediction by the model.

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Experimental Investigation of Surge Phenomena in a Transonic Centrifugal Compressor With Inlet Distortion

Volume 2E: Turbomachinery ◽

10.1115/gt2020-15426 ◽

2020 ◽

Author(s):

Sasuga Ito ◽

Masato Furukawa ◽

Satoshi Gunjishima ◽

Takafumi Ota ◽

Kazuhito Konishi ◽

...

Keyword(s):

Flow Rate ◽

Centrifugal Compressor ◽

Flow Instability ◽

Pressure Sensors ◽

Low Flow ◽

Inlet Distortion ◽

Transonic Centrifugal Compressor ◽

Response Pressure ◽

Surge Phenomena ◽

Low Flow Rate

Abstract Inlet distortion has influence on the aerodynamic performance of turbomachinery such as compressors, turbines and fans. On turbochargers, bent pipes are installed around the compressor due to the spatial limitations in the engine room of the vehicle. As the result, the compressor is operated with the distorted inflow. In the low flow rate operation, the distorted inflow also affects the flow instability like stall and surge. Especially, the operation range on the low flow rate side is defined based on the flow rate where surge occurs, so it is important to investigate the effect of the distorted inflow on surge. In this study, the effect of the inlet distortion to surge phenomena has been investigated by the experiments with a transonic centrifugal compressor. A bent pipe has been installed at the upstream of the compressor to generate a distorted flow. Experiments have been also conducted under the condition that a straight pipe was installed upstream of the compressor, and unsteady measurements with high response pressure sensors and an I-type hot wire probe have been carried out to each experiments. In addition, Fast Fourier transform (FFT) and Wavelet transform have been applied to the unsteady measurement results obtained from each experiment.

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A Comparative Assessment of Spalart-Shur Rotation/Curvature Correction in RANS Simulations in a Centrifugal Pump Impeller

Mathematical Problems in Engineering ◽

10.1155/2014/342905 ◽

2014 ◽

Vol 2014 ◽

pp. 1-9 ◽

Cited By ~ 5

Author(s):

Ran Tao ◽

Ruofu Xiao ◽

Wei Yang ◽

Fujun Wang

Keyword(s):

Kinetic Energy ◽

Centrifugal Pump ◽

Flow Rate ◽

Comparative Assessment ◽

Turbulence Kinetic Energy ◽

Low Flow ◽

Pump Impeller ◽

Curvature Correction ◽

Centrifugal Pump Impeller ◽

Low Flow Rate

RANS simulation is widely used in the flow prediction of centrifugal pumps. Influenced by impeller rotation and streamline curvature, the eddy viscosity models with turbulence isotropy assumption are not accurate enough. In this study, Spalart-Shur rotation/curvature correction was applied on the SSTk-ωturbulence model. The comparative assessment of the correction was proceeded in the simulations of a centrifugal pump impeller. CFD results were compared with existing PIV and LDV data under the design and low flow rate off-design conditions. Results show the improvements of the simulation especially in the situation that turbulence strongly produced due to undesirable flow structures. Under the design condition, more reasonable turbulence kinetic energy contour was captured after correction. Under the low flow rate off-design condition, the prediction of turbulence kinetic energy and velocity distributions became much more accurate when using the corrected model. So, the rotation/curvature correction was proved effective in this study. And, it is also proved acceptable and recommended to use in the engineering simulations of centrifugal pump impellers.

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