Experimental Investigation of Flow Instabilities and Rotating Stall in a High-Energy Centrifugal Pump Stage

Berten, Stefan; Dupont, P.; Fabre, Laurent; Kayal, Maher; Avellan, François; Farhat, Mohamed

doi:10.1115/fedsm2009-78562

Cited by 31 publications

(24 citation statements)

References 10 publications

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“…The fast Fourier transform (FFT) method was applied to analyze the pressure signals. The pressure normalization c p was defined as Equation (23), in which the U 2 is the rotating velocity at the impeller outlet [45]. Both, the time history and frequency domain of the monitor points pbt5 and FCA1, from the numerical and experimental results, at 1.0 × Q 0 and 0.8 × Q 0 operating conditions, are shown in Figure 7, where n represents the rotating frequency.…”

Section: Validation Of Numerical Simulating Resultsmentioning

confidence: 99%

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

et al. 2019

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Dredge pumps are usually operated at part-load conditions, in which the low-solidity centrifugal impeller could experience large internal energy dissipation, related to flow separation and vortices. In this study, SST k-ω and SAS-SST turbulence models were used, in steady and unsteady simulations, for a low-head centrifugal pump with a three-bladed impeller. The main focus of the present work was to investigate the internal energy dissipation in rotating an impeller at part-load operating conditions, related to flow separation and stall. The unsteady nature of these operating conditions was investigated. Performance experiments and transient wall pressure measurements were conducted for validation. A methodology for internal energy dissipation analysis has been proposed; and the unsteady pressure fluctuations were analyzed in the rotating impeller. The internal power losses in the volute and the impeller were mostly found in the centrifugal pump. The rotating stall phenomenon occurred with flow separation and detachment at the part-load operating condition, leading to a dissipation of the internal energy in the impeller. The rotating impeller experienced pressure fluctuations with low frequencies, at part-load operating conditions, while in the design operating condition only experienced rotating frequency.The energy loss in the centrifugal pump could be divided into flow dissipation, disk friction, and discharge leakage loss. Kara Omar et al. [7] calculated the losses through empirical and semi-empirical models, and verified them with experimental results. El-Naggar [8] conducted an experimental one-dimensional flow analysis and predicted the pump performance in a dimensionless form. Klas et al. [9] performed simulations on a centrifugal pump and investigated the energy loss in different flow components, to detect the influence of the component geometry. These studies focused on the whole energy transformation in flow components, without a detailed loss analysis.The inner flow characteristic was investigated as the energy loss reasons for centrifugal pumps. Posa et al. [10] investigated the streamline distribution on the impeller blade surface and found that a stall phenomenon developed near the impeller shroud. Zhang et al. [11] applied velocity vector distribution to detect the flow pattern near the volute tongue, and to discuss its effects on the efficiency fluctuation of a centrifugal pump. Barrio et al. [12] detected a counter-rotating vortex near the interface between the impeller and the volute, through velocity distribution. Pacot et al. [13] used the pressure distribution to explore the stall propagation mechanism. Asim et al. [14] applied the Q-criterion to illustrate that a secondary flow generated near the volute tongue, with an impact on the pump head. Miorini et al. [15] and Zhou et al.[16] adopted a vorticity study to investigate tip leakage flow and rotating stall, respectively, to describe the development of these unsteady flow phenomena and to prove their effects on pump performance. These m...

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Section: Validation Of Numerical Simulating Resultsmentioning

confidence: 99%

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

et al. 2019

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“…The dominate frequency is a very-low stall frequency f TEv which is about 1/5 f imp . It is mainly and strongly influenced by the stable stalled vortex structure which is similar as in the rotating stall cases [ 36 , 37 ]. Figure 11 d is on P 4 which is in the diffuser blade trailing-edge wake.…”

Section: Transient Flow Field Analysis At Lower-loadmentioning

confidence: 99%

Evaluating the Transient Energy Dissipation in a Centrifugal Impeller under Rotor-Stator Interaction

Tao

Zhao

Wang

2019

Entropy

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In fluid machineries, the flow energy dissipates by transforming into internal energy which performs as the temperature changes. The flow-induced noise is another form that flow energy turns into. These energy dissipations are related to the local flow regime but this is not quantitatively clear. In turbomachineries, the flow regime becomes pulsating and much more complex due to rotor-stator interaction. To quantitatively understand the energy dissipations during rotor-stator interaction, the centrifugal air pump with a vaned diffuser is studied based on total energy modeling, turbulence modeling and acoustic analogy method. The numerical method is verified based on experimental data and applied to further simulation and analysis. The diffuser blade leading-edge site is under the influence of impeller trailing-edge wake. The diffuser channel flow is found periodically fluctuating with separations from the blade convex side. Stall vortex is found on the diffuser blade trailing-edge near outlet. High energy loss coefficient sites are found in the undesirable flow regions above. Flow-induced noise is also high in these sites except in the stall vortex. Frequency analyses show that the impeller blade frequency dominates in the diffuser channel flow except in the outlet stall vortexes. These stall vortices keep their own stall frequency which is about 1/5 impeller frequency with high energy loss coefficient but low noise level. Results comparatively prove the energy dissipation mechanism in the centrifugal air pump under rotor-stator interaction. Results also provide the quantitative basis for turbomachinery’s loss reduction design.

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“…A reference solution from experiments f EXP is introduced so that only solutions obtained from two successively refined meshes are necessary to show mesh independence. For this study, the grid refinement ratio r = (N 2 /N 1 ) 1/3 between respective meshes is r h h = = 1 2 2 , where h denotes the grid spacing.…”

Section: Grid Independence Studymentioning

confidence: 99%

“…A very slow rotating stall in the diffuser channel rotating at 1% of the impeller rotational speed was observed in [2] by performing experimental analysis with a centrifugal pump (n q = 21rpm) at Q/Q n = 0.8. Similar observations at a flow rate Q/Q n = 0.8 are reported in [3] and also [4,5] who revealed the onset of rotating stall phenomena.…”

Section: Introductionmentioning

confidence: 99%

Simulation and Experimental Investigation of the Stay Vane Channel Flow in a Reversible Pump Turbine at Off-Design Conditions

Erne

Edinger

Maly

et al. 2017

Period. Polytech. Mech. Eng.

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IntroductionIncreasing the operational flexibility of a pumped storage power plant often involves an extension of the continuous operating range of the pump turbine. Also, large head variations are mostly associated with a wide off-design operating range. This makes it necessary to ensure off-design operating characteristics with low fluid dynamical effects at a high degree of reliability. Especially during pump mode, part-load flow conditions can cause periodically unsteady flow patterns in the distributor section of the pump turbine. The occurrence of such unsteady flow phenomena upstream of the runner like stalling flow or Rotor-Stator-Interaction were investigated by many authors in the past.Mesquita and Ciocan [1] are one of the few authors, who studied the flow in the stay vane channel of a pump turbine focusing on the flow between guide vanes and stay vanes.A very slow rotating stall in the diffuser channel rotating at 1% of the impeller rotational speed was observed in [2] by performing experimental analysis with a centrifugal pump (n q = 21rpm) at Q/Q n = 0.8. Similar observations at a flow rate Q/Q n = 0.8 are reported in [3] and also [4,5] who revealed the onset of rotating stall phenomena. Furthermore, at a partload flow rate Q/Q n = 0.77, Zhang [6] detected by means of instationary LDV-measurements a significant frequency peak at 1-2Hz, induced by periodically unsteady flow.In this work, several off-design operating points are analyzed to get information on the flow behavior in the stay vane channel, including zero-flow and full-load conditions. Measurements of a model pump turbine are used to assess the capability of the simulations to predict transient flow mechanisms. LDV technique is applied to the model pump turbine which provides optical accessibility in the spiral case.A detailed analysis of several quantities at operating point Q/Q n = 0.74 allows a better understanding of the substantially altering flow patterns close to the stay vane channel. This also makes it possible to draw conclusions about the influence of stalled flow on the global flow behavior in the distributor.The following work is based on the paper submitted at the CMFF15 [7].

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Experimental Investigation of Flow Instabilities and Rotating Stall in a High-Energy Centrifugal Pump Stage

Cited by 31 publications

References 10 publications

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

Unsteady Flow Numerical Simulations on Internal Energy Dissipation for a Low-Head Centrifugal Pump at Part-Load Operating Conditions

Evaluating the Transient Energy Dissipation in a Centrifugal Impeller under Rotor-Stator Interaction

Simulation and Experimental Investigation of the Stay Vane Channel Flow in a Reversible Pump Turbine at Off-Design Conditions

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