scholarly journals Investigation of flow instability characteristics in a low specific speed centrifugal pump using a modified partially averaged Navier–Stokes model

2019 ◽  
Vol 233 (7) ◽  
pp. 834-848 ◽  
Author(s):  
Weixiang Ye ◽  
Xianwu Luo ◽  
Renfang Huang ◽  
Zhiwu Jiang ◽  
Xiaojun Li ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Flow Separation ◽  
Flow Instability ◽  
Rotating Stall ◽  
Navier Stokes ◽  
Separation Flow ◽  
Pump Impeller ◽  
Part Load ◽  
Operation Conditions ◽  
Vorticity Transport

In this study, a modified partially averaged Navier–Stokes (MPANS) model is applied to investigate the flow instability characteristics in a low specific centrifugal pump. In MPANS model, the unresolved-to-total ratio of kinetic energy fk is determined according to the local grid size and turbulence length scale. The numerical results by MPANS model are compared with that simulated by SST k-ω model and the available experimental data. It is noted that MPANS model shows better performance for investigating the unstable flow in the current pump under part-load operation conditions. The time-averaged internal flow and flow incidence in the pump impeller depicts that with the decreasing flow coefficient, flow separation develops in the impeller. Owing to the strong separation flow as well as vortex evolution, incidence angle is large and varies remarkably at the entrance of blade-to-blade passage in the pump impeller. The evolution dynamics of rotating stall is further discussed in detail based on vorticity transport equation. During the evolution of rotating stall, the vortex stretching term has an important effect on vorticity transport under the part-load conditions. The analysis of the pressure fluctuations excited by periodic evolution of rotating stall shows that the rotating stall cell propagates along the rotational direction, and identifies the rotating stall frequency ( fstall), which is much lower than the rotational frequency of the impeller, fn ( fstall = 8.76% fn). Finally, two-dimensional Lagrangian coherent structure (LCS) is used to reveal the separation flow in blade-to-blade passages of the pump by monitoring the trajectory of the particles. Both LCS and vortex structure by λ2 can clearly demonstrates the passage blockage and flow separation under the part-load operation conditions, depicting that the separation flow occurs at blade suction side and develops from the leading edge to the main passage in the impeller.

scholarly journals Instability analysis for a centrifugal pump with straight inlet pipe using partially averaged Navier–Stokes model

2020 ◽  
pp. 095765092091954
Author(s):  
Weixiang Ye ◽  
Zhongdong Qian ◽  
Renfang Huang ◽  
Xiaojun Li ◽  
Zuchao Zhu ◽  
...  
Keyword(s):  
Flow Instability ◽  
Load Condition ◽  
Head Loss ◽  
Rotating Stall ◽  
Navier Stokes ◽  
Positive Slope ◽  
Inlet Pipe ◽  
Pump Impeller ◽  
Blade Passage ◽  
Part Load

The current study numerically investigates the flow instability under several part-load conditions in a centrifugal pump with a straight inlet pipe to explore the underlying relationship between a positive slope phenomenon and internal flow using a partially averaged Navier–Stokes model. The model was validated by comparing the hydraulic performance and averaged flow in the impeller between the numerical results and experimental data of a tested pump. The internal flows in pumps have been intensively investigated based on Batchelor vortex family, Rayleigh–Taylor criterion, entropy generation rate, and energy equation to analyze the flow instability from different aspects. The simulation results using partially averaged Navier–Stokes model are acceptable due to the good agreement with the experimental data for the tested pump. No matter the geometry of the inlet pipe, the pre-swirling flows in the inlet pipe are in the convective instability region. Under the part-load condition of φ = 0.5 φbep, the axial vorticity coefficient is affected by the geometry of the inlet pipe. However, under the part-load condition with rotating stall, e.g. φ = 0.78 φbep, the flow in the inlet pipe is affected by the unstable flow in the pump impeller. For the pump with a straight inlet pipe, the vortex inside the blade-to-blade passage is in a stable state according to Rayleigh–Taylor criterion under the condition of φ = 0.5 φbep. However, the vortex in the blade-to-blade passage is in an unstable state due to centrifugal instability under those operation conditions with rotating stall cells in the impeller, and the dominant oscillations are dependent on the propagation of rotating stall cells. Finally, head loss analysis based on energy equations elucidates that turbulent kinetic energy production term is predominant in the head loss in pump impeller. The present results are helpful for better understanding of the unstable flows and positive slope phenomenon for centrifugal pumps.

scholarly journals Investigation of flow separation in a centrifugal pump impeller based on improved delayed detached eddy simulation method

2019 ◽  
Vol 11 (12) ◽  
pp. 168781401989783
Author(s):  
Yun Ren ◽  
Zuchao Zhu ◽  
Denghao Wu ◽  
Xiaojun Li ◽  
Lanfang Jiang
Keyword(s):  
Large Eddy Simulation ◽  
Centrifugal Pump ◽  
Flow Separation ◽  
Hybrid Algorithm ◽  
Internal Flow ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Reynolds Averaged Navier Stokes ◽  
Vorticity Flux

The mechanism of flow separation in the impeller of a centrifugal pump with a low specific speed was explored by experimental, numerical, and theoretical methods. A novel delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm combined with a rotation and curvature correction method was developed to calculate the inner flow field of the original pump for the large friction loss in the centrifugal impeller, high adverse pressure gradient, and large blade curvature. Boundary vorticity flux theory was introduced for internal flow diagnosis, and the relative velocity vector near the surface of the blade and the distribution of the dimensionless pressure coefficient was analyzed. The validity of the numerical method was verified, and the location of the backflow area and its flow features were determined. Finally, based on flow diagnosis, the geometric parameters influencing the flow state of the impeller were specifically adjusted to obtain a new design impeller. The results showed that the distribution of the boundary vorticity flux peak values, the skin friction streamline, and near-wall relative velocities improved significantly after the design change. In addition, the flow separation was delayed, the force applied on the blade was improved, the head under the part-load condition was improved, and the hydraulic efficiency was improved over the global flow ranges. It was demonstrated that the delayed Reynolds-averaged Navier–Stokes/large eddy simulation hybrid algorithm was capable to capture the separation flow in a centrifugal pump, and the boundary vorticity flux theory was suitable for the internal flow diagnosis of centrifugal pump.

Investigation of rotating stall for a centrifugal pump impeller using various SGS models

2017 ◽  
Vol 29 (2) ◽  
pp. 235-242 ◽  
Author(s):  
Pei-jian Zhou ◽  
Fu-jun Wang ◽  
Zheng-jun Yang ◽  
Jie-gang Mou
Keyword(s):  
Centrifugal Pump ◽  
Rotating Stall ◽  
Pump Impeller ◽  
Centrifugal Pump Impeller

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

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 2013 ◽  
Author(s):  
Xiaoran Zhao ◽  
Yongyao Luo ◽  
Zhengwei Wang ◽  
Yexiang Xiao ◽  
François Avellan
Keyword(s):  
Energy Dissipation ◽  
Internal Energy ◽  
Centrifugal Pump ◽  
Flow Separation ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Operating Condition ◽  
Part Load ◽  
Rotating Impeller ◽  
Low Head

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.

Comparative modeling and analysis of the flow asymmetricity in a centrifugal pump impeller at partial load

2019 ◽  
Vol 234 (2) ◽  
pp. 237-247 ◽  
Author(s):  
Ran Tao ◽  
Zhengwei Wang
Keyword(s):  
Flow Regime ◽  
Centrifugal Pump ◽  
Channel Flow ◽  
Pressure Pulsation ◽  
Rotating Stall ◽  
Pressure Pulsations ◽  
Pump Impeller ◽  
Partial Load ◽  
Load Conditions ◽  
Centrifugal Pump Impeller

Undesirable flow regime occurs at partial-load conditions of the centrifugal pump. Flow separates at the leading edge and pulses in the blade channel with complex stall cell transfer law. The passing capability of the blade channel becomes important when rotating stall happens. In this study, the blade channel number influence on the flow stability in a centrifugal pump impeller was studied by unsteady flow simulations after numerical-experimental verification. The 5-, 6-, and 7-blade impellers were discussed under the same partial-load flow rate condition and the same rotating speed. Results show that the internal flow pattern was strongly influenced by the blade channel number. Periodic half-blockage was observed in the 5-blade impeller. Alternating stall with three stalled and three well-behaved channels existed in the 6-blade impeller. Complex aperiodic flow pattern occurred in the 7-blade impeller with the well-behaved, half-blocked, and fully stalled passages were all observed with stall cell transfer. The different flow regime caused different pressure pulsations. In the 5-blade impeller, the inter-channel flow frequencies, which were induced by the fluid extruded from blocked channels flowed into other channels, dominated. In the 6-blade impeller, the pressure pulsations performed low-in-amplitude and high-in-frequency. The flow regime was stable even under the rotating stall. In the 7-blade impeller, the rotating stall frequency dominated. The inter-channel flow frequencies were also obvious. The stable rotating stall pattern does not strongly influence the pressure pulsation and impeller axial and radial forces. The transferring stall cell induces extra mild pressure pulsation and impeller forces. The inter-channel flow adds strong pressure pulsation and impeller forces. When centrifugal pumps are operating at partial-load conditions, the flow characters especially the inter-channel flow caused by half-channel-blockage should be checked to avoid operation instability and security.

Measurements of Rotating Stall Inside a Centrifugal Pump Impeller

2005 ◽  
Author(s):  
D. A. Johnson ◽  
N. Pedersen ◽  
C. B. Jacobsen
Keyword(s):  
Centrifugal Pump ◽  
Marked Change ◽  
Rotating Stall ◽  
Velocity Measurements ◽  
Pump Impeller ◽  
Pressure Transducers ◽  
Design Load ◽  
Measured Flow ◽  
Flow Through ◽  
Centrifugal Pump Impeller

Velocity measurements have been obtained in a centrifugal pump with a volute. The measurements have been obtained between the blade passages of a shrouded impeller and in the volute region using laser Doppler velocimetry (LDV). Complimentary measurements have been obtained with pressure transducers circumferentially mounted on the volute. The flow through the impeller is measured at both design load and at several off-design conditions including severe off-design conditions. Results show that flow behaviour at design conditions Qd is well behaved. At reduced flow off-design conditions (0.25Qd) the measured flow pattern was altered significantly showing alternating stable stationary stalled and unstalled passages. Spectral analysis of the data from the LDV probe and the pressure probes showed a marked change in the spectrum as the stall phenomena occurs. This result is in contrast with previous researchers who have reported partially stalled flow passages or rotating stall conditions where the stall pattern rotated relative to the impeller with a regular frequency.

scholarly journals Numerical Investigation of a First Stage of a Multistage Centrifugal Pump: Impeller, Diffuser with Return Vanes, and Casing

2013 ◽  
Vol 2013 ◽  
pp. 1-15
Author(s):  
Nicolas La Roche-Carrier ◽  
Guyh Dituba Ngoma ◽  
Walid Ghie
Keyword(s):  
Numerical Investigation ◽  
Centrifugal Pump ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Pump Impeller ◽  
Impeller Blade ◽  
Navier Stokes Equations ◽  
Wall Functions ◽  
Multistage Centrifugal Pump ◽  
Pump Head

This paper deals with the numerical investigation of a liquid flow in a first stage of a multistage centrifugal pump consisting of an impeller, diffuser with return vanes, and casing. The continuity and Navier-Stokes equations with the k-ε turbulence model and standard wall functions were used. To improve the design of the pump's first stage, the impacts of the impeller blade height and diffuser vane height, number of impeller blades, diffuser vanes and diffuser return vanes, and wall roughness height on the performances of the first stage of a multistage centrifugal pump were analyzed. The results achieved reveal that the selected parameters affect the pump head, brake horsepower, and efficiency in a strong yet different manner. To validate the model developed, the results of the numerical simulations were compared with the experimental results from the pump manufacturer.

scholarly journals Numerical Flow Simulation in a Centrifugal Pump at Design and Off-Design Conditions

2007 ◽  
Vol 2007 ◽  
pp. 1-8 ◽  
Author(s):  
K. W. Cheah ◽  
T. S. Lee ◽  
S. H. Winoto ◽  
Z. M. Zhao
Keyword(s):  
Centrifugal Pump ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Internal Flow ◽  
Leading Edge ◽  
Design Flow ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Pump Impeller ◽  
Rate Condition

The current investigation is aimed to simulate the complex internal flow in a centrifugal pump impeller with six twisted blades by using a three-dimensional Navier-Stokes code with a standardk-εtwo-equation turbulence model. Different flow rates were specified at inlet boundary to predict the characteristics of the pump. A detailed analysis of the results at design load,Qdesign, and off-design conditions, Q = 0.43Qdesignand Q = 1.45Qdesign, is presented. From the numerical simulation, it shows that the impeller passage flow at design point is quite smooth and follows the curvature of the blade. However, flow separation is observed at the leading edge due to nontangential inflow condition. The flow pattern changed significantly inside the volute as well, with double vortical flow structures formed at cutwater and slowly evolved into a single vortical structure at the volute diffuser. For the pressure distribution, the pressure increases gradually along streamwise direction in the impeller passages. When the centrifugal pump is operating under off-design flow rate condition, unsteady flow developed in the impeller passage and the volute casing.

scholarly journals Influence of Blade Leading-Edge Shape on Rotating-Stalled Flow Characteristics in a Centrifugal Pump Impeller

2020 ◽  
Vol 10 (16) ◽  
pp. 5635
Author(s):  
Hongying Luo ◽  
Ran Tao ◽  
Jiandong Yang ◽  
Zhengwei Wang
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Incidence Angle ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Rotating Stall ◽  
Pump Impeller ◽  
The Impact ◽  
Centrifugal Pump Impeller ◽  
Blade Leading Edge

Rotating stall, which is a common phenomenon in turbomachinery, strongly relates to the flow rate condition. In centrifugal impellers, rotating stall was induced by the incidence angle on blade leading-edge at partial-load. The blade leading-edge shape also influences the rotating stall because of the subtle change of local flow-field. In this study, the influence of blade leading-edge shape on rotating-stalled flow characteristics was studied in a six-blade centrifugal pump impeller. The stall pattern was “alternating”: Three passages were stalled, three passages were well-behaved, and the stalled and well-behaved passages occurred alternately. The stalled flow characteristics can be studied without the interruption of stall cell movement. Four types of blade leading-edge (blunt, sharp, ellipse, and round) were numerically compared based on the initial typical impeller and the numerical–experimental verification. The numerical comparison shows that the leading-edge shape has a strong influence on the stalled flow pattern, velocity, pressure, turbulence kinetic energy, and flow-induced noise inside impellers. The blunt and sharp leading-edge impellers had a similar internal pattern; the ellipse and round leading-edge impellers were also similar in the internal flow-field. Pressure pulsation analysis showed more obvious differences among these impellers. The main frequency and the pulsation peak–peak values were completely different because of the slight leading-edge shape differences. It revealed the impact of leading-edge geometry on the transient flow-field change under the same incidence angle conditions. It also provided reference for influencing or controlling the rotating stall by blade profile design.

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