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.

Investigation of Hydrodynamic Forces on Rotating and Whirling Centrifugal Pump Impellers

1996 ◽  
Author(s):  
R. Fongang ◽  
J. Colding-Jørgensen ◽  
R. Nordmann
Keyword(s):  
Centrifugal Pump ◽  
Fluid Model ◽  
Hydrodynamic Forces ◽  
Operating Conditions ◽  
Good Prediction ◽  
Single Vortex ◽  
Unsteady Forces ◽  
Fluid Forces ◽  
Rotordynamic Coefficients ◽  
Rotating Impeller

A 2-dimensional fluid model is developed to investigate the hydrodynamic forces exerted on a rotating impeller caused by the impeller-fluid-volute interaction in a centrifugal pump. In this model, the impeller periphery and the volute contour are replaced by a distribution of unsteady vortices. The impeller center is assumed to execute a whirling motion about the rotor center. This is an improvement of the earlier quasisteady flow model of Colding-Jørgensen (1980) where the impeller was taken as a single vortex-source point. The forces can be presented as a sum of a steady and an unsteady part. The rotordynamic coefficients are deduced from the unsteady forces decomposed into radial and tangential components relative to the orbit described by the impeller center. In comparison to most of the theoretical and experimental results found in the literature, the model seems to give good prediction. It appears clearly from this analysis that, under certain operating conditions, the fluid forces on the impeller have a destabilizing effect on the pump rotor.

Investigation of Hydrodynamic Forces on Rotating and Whirling Centrifugal Pump Impellers

1998 ◽  
Vol 120 (1) ◽  
pp. 179-185 ◽  
Author(s):  
R. Fongang ◽  
J. Colding-Jo̸rgensen ◽  
R. Nordmann
Keyword(s):  
Centrifugal Pump ◽  
Fluid Model ◽  
Hydrodynamic Forces ◽  
Operating Conditions ◽  
Good Prediction ◽  
Single Vortex ◽  
Unsteady Forces ◽  
Fluid Forces ◽  
Rotordynamic Coefficients ◽  
Rotating Impeller

A two-dimensional fluid model is developed to investigate the hydrodynamic forces exerted on a rotating impeller caused by the impeller-fluid-volute interaction in a centrifugal pump. In this model, the impeller periphery and the volute contour are replaced by a distribution of unsteady vortices. The impeller center is assumed to execute a whirling motion about the rotor center. This is an improvement of the earlier quasi-steady flow model of Colding-Jo̸rengsen (1980) where the impeller was taken as a single vortex source point. The forces can be presented as a sum of a steady and an unsteady part. The rotordynamic coefficients are deduced from the unsteady forces decomposed into radial and tangential components relative to the orbit described by the impeller center. In comparison to most of the theoretical and experimental results found in the literature, the model seems to give good prediction. It appears clearly from this analysis that, under certain operating conditions, the fluid forces on the impeller have a destabilizing effect on the pump rotor.

Effect of outlet impeller diameter on performance prediction of centrifugal pump under single-phase and cavitation flow conditions

2022 ◽  
Vol 0 (0) ◽  
Author(s):  
Ahmed Ramadhan Al-Obaidi ◽  
Ali Qubian
Keyword(s):  
Frequency Domain ◽  
Centrifugal Pump ◽  
Pressure Fluctuation ◽  
Single Phase ◽  
Static Pressure ◽  
Volume Fraction ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Maximum Pressure ◽  
Velocity Magnitude

Abstract In this current study, the transient numerical calculations using CFD code are carried out under different outlet impeller diameters for the flow field within a centrifugal pump under single-phase and cavitation conditions. Both qualitative and quantitative analyses are carried out on all of these results in order to better understand the flow structure within a centrifugal pump. Also, the investigations using different outlet impeller diameters configurations relating to the static pressure, velocity magnitude, vapour volume fraction variations, as well as pressure fluctuations in both time and frequency domain at the impeller and volute of the pump are analysed. Velocity and static pressure variations of the pump under different outlet impeller diameters range (200, 210 and 220 mm) are investigated. Reliable model is developed and validated, at various pump operating conditions, to analyse the characteristics of pressure fluctuations in both time and frequency domain. Cavitation occurrence, under different outlet impeller diameters and flow rates, are detected and correlated, using a CFD model (volume fraction distributions). Based on the developed model’s findings, at the set operating conditions ranges, the distribution and impact (cavitation and head-wises) of both the pressure and velocity are analysed. The average pressure fluctuation in the volute for do = 210 mm is higher than for do = 200 mm by about 6.74%, also the maximum pressure fluctuation for do = 220 mm is higher than for do = 210 mm by around 7.4%. Furthermore, the maximum pressure fluctuation in the impeller for do = 210 mm is higher than for do = 200 mm by 12.48%, also for do = 220 mm is higher than for do = 210 mm by 10.8%. The developed CFD models are proved valuable tools in identifying and optimizing the pump performance and characterization. The head for when do = 220 mm is higher than for when do = 200 mm under both single-phase and cavitation conditions by around 14.13% and 14.69%. The maximum pressure fluctuation for do = 200 mm is lower than for do = 210 mm by 41.58%. Furthermore, the maximum pressure fluctuation at the impeller for do = 220 mm is higher than the two models. There is a small clearance between the impeller and the volute for this model, leading to the pressure fluctuation amplitudes being higher than the other above models.

scholarly journals An Experimental Study on the Fluid Forces Induced by Rotor-Stator Interaction in a Centrifugal Pump

2003 ◽  
Vol 9 (2) ◽  
pp. 135-144 ◽  
Author(s):  
Shijie Guo ◽  
Hidenobu Okamoto
Keyword(s):  
Centrifugal Pump ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Strong Relationship ◽  
Operating Conditions ◽  
Flow Rates ◽  
Fluid Forces ◽  
Large Pressure ◽  
Rotor Stator Interaction ◽  
Frequency Components

The pressure fluctuations and the radial fluid forces acting on the impeller, the pressures in the volute, as well as the vibration of the shaft in a centrifugal pump were measured simultaneously, and their relationship was investigated. Experiments were done for various diffuser vanes, flow rates, and rotating speeds. It was demonstrated that both the blade-pressure fluctuations and the volute static pressures are nonuniform circumferentially (not axisymmetrical) under off-design operating conditions and that the two have a strong relationship. At high flow rates, the blade pressure fluctuations, induced by rotor-stator interactions, are large in areas where the volute static pressure is low. The traveling directions of the rotating pressure waves, the whirling directions of the radial fluid forces, and the most predominant frequency components of both the fluctuations and the forces are discussed, and an equation for predicting them is introduced. It was also noted that large alternating fluid forces are not necessarily associated with large pressure fluctuations. Furthermore, when measuring the radial fluid forces in the rotating frame, other frequency components, in addition to those related to the products of the diffuser vane number and the rotating frequency, may occur due to the circumferential unevenness of the pressure fluctuations on the impeller. These components are predictable.

Thermodynamic analysis of energy dissipation and unsteady flow characteristic in a centrifugal dredge pump under over-load conditions

2019 ◽  
Vol 233 (13) ◽  
pp. 4742-4753 ◽  
Author(s):  
Xiaoran Zhao ◽  
Zhengwei Wang ◽  
Yexiang Xiao ◽  
Yongyao Luo
Keyword(s):  
Energy Dissipation ◽  
Unsteady Flow ◽  
Numerical Simulations ◽  
Pressure Fluctuation ◽  
Large Angle ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Operating Condition ◽  
High Entropy ◽  
Flow Phenomena

The present paper aims to investigate the energy dissipation related to unsteady flow phenomena inside a three-bladed impeller of a centrifugal dredge pump under over-load operating conditions. Three-dimensional unsteady numerical simulations of the centrifugal pump are performed by adopting the SAS SST-curvature correction turbulence model with the total energy equation. The simulating results are verified by comparing the performance results and pressure fluctuation with available experimental data. The unsteady flow patterns and energy dissipation in the rotating impeller are analysed by entropy distribution and pressure fluctuation spectra. A high-entropy area appears in the impeller flow passage when the discharge increases. It is indicated in the unsteady simulation results that a vortex flow with high entropy generates and detaches periodically, which causes the hydraulic energy loss under over-load operating conditions. In numerical simulations, a frequency as 3.3 times of rotating frequency is found in the pressure spectral analysis at 1.45 Q0 operating condition, which is related to the unsteady flow structure. The secondary flow near the volute tongue is found at 1.45 Q0 operating condition due to the large angle of attack when discharge increases.

Investigation of Pressure Losses and Flow Fluctuations in an Intercept Valve Assembly of an Intermediate-Pressure Turbine Part

2020 ◽  
Author(s):  
Vaclav Slama ◽  
Lukas Mrozek ◽  
Bartolomej Rudas ◽  
David Simurda ◽  
Jindrich Hala ◽  
...  
Keyword(s):  
Flow Separation ◽  
Pressure Loss ◽  
Pressure Fluctuations ◽  
Control Valve ◽  
Operational Reliability ◽  
Operating Conditions ◽  
Pressure Losses ◽  
Flow Fluctuations ◽  
Valve Assembly ◽  
Valve Model

Abstract A new design of an intercept valve assembly of the intermediate-pressure turbine part of greater power output is investigated in terms of pressure losses and flow fluctuations by using measurement on an experimental valve model. In addition, numerical simulations are used to further clarify measured phenomena. For such valve assemblies, it is important to exactly predict pressure losses and avoid danger of vibrations, which are caused by undesirable flow fluctuations, in order to guarantee valve’s efficiency and operational reliability. For this type of valve, it is especially important for turbine operations in partial loads (off-design conditions). Measurements were carried out in the Aerodynamic laboratory of the Institute of Thermomechanics of the Czech Academy of Sciences (IT) in a modular aerodynamic tunnel. Numerical simulations were carried out in the Doosan Skoda Power Company (DSP) by using a package of ANSYS software tools. The experimental valve model is a scaled model of a real valve assembly. It consists of an inlet pipeline, a stop valve and a control valve including its diffuser and outlet pipeline. Measured regimes were defined by a mass flow rate and a control valve cone lift which can be precisely changed. In order to investigate pressure loses, total and static pressures at valve characteristic locations were measured by using Prandtl probes and wall static pressure taps. In order to measure pressure fluctuations, Kulite fast response pressure transducers were used. They were situated near the valve throat where the flow fluctuations, which are strongly related to a flow separation, are the most visible and influential. Measurement results are compared with numerical results and locations with a flow separation were found. In order to reduce this phenomenon, different valve seat angles were also tested. As a result, a valve design could be optimized and, for a pressure loss prediction, a pressure loss model for this new intercept valve assembly could be created. Therefore, pressure losses in similar valve assemblies can be predicted with required accuracy for each new turbine where modern intercept valves are used. This helps to increase steam turbine efficiency and reduce fuel consumption. Based on pressure fluctuations results, operating conditions at which dangerous flow instabilities occur were identified. It was concluded that there is an operating condition border where the flow field starts to be unstable. As a result, the areas of safe and dangerous operating conditions can be predicted so that the operational reliability of the valve can be guaranteed.

Combustion and Exhaust Emission Characteristics of a Passenger Car Diesel Engine Fueled With Biodiesel 30% Derived From Soybean

2010 ◽  
Author(s):  
Myung Yoon Kim ◽  
WooHeum Cho ◽  
Eun-Hyun Lee ◽  
Jerok Chun
Keyword(s):  
Diesel Engine ◽  
Diesel Fuel ◽  
Operating Conditions ◽  
Engine Management System ◽  
Exhaust Gas ◽  
Operating Condition ◽  
Part Load ◽  
Full Load ◽  
The Impact ◽  
Engine Power

The impact of soybean methyl ester (SME) on the injection mass curve, exhaust emissions, engine performance, and exhaust gas temperatures of a common-rail direct injection diesel engine have been investigated. In this study, 30% SME blended diesel fuel (BD30) has been used as a fuel in the engine and results of the investigation were compared to those obtained using petroleum diesel fuel. The results of the investigation show that the change in injection mass curve when using BD30 instead of diesel was insignificant. A combustion analysis shows BD30 has a shorter ignition delay at part-load operating condition where heavy exhaust gas recirculation (EGR) rate is used. This difference in behavior is due to the oxygen contents and lower stoichiometric air-fuel ratio of BD30, which leads to higher O2 concentration in the exhaust gas. At part-load operating conditions, BD30 results showed 53% reduction in smoke at the expense of 18% increase in NOx emission. The full load engine power for BD30 was decreased by 2.1∼3.8% using EMS (engine management system) configurations without torque adjustment to compensated reduction in calorific value of BD30. When the engine power was so adjusted that BD30 produced the same power as diesel fuel, a lower exhaust gas temperature was observed at full load operating condition. Considering that the LHV (lower heating value) of BD30 is 2.6% lower than that of diesel fuel, there may be no factors that cause deterioration of thermal efficiency on using BD30 under all operating conditions.

Transient Behavior of a Cavitating Centrifugal Pump at Rapid Change in Operating Conditions—Part 2: Transient Phenomena at Pump Startup/Shutdown

1999 ◽  
Vol 121 (4) ◽  
pp. 850-856 ◽  
Author(s):  
T. Tanaka ◽  
H. Tsukamoto
Keyword(s):  
Centrifugal Pump ◽  
Pressure Fluctuations ◽  
Rapid Change ◽  
Transient Behavior ◽  
Operating Conditions ◽  
Pressure Oscillations ◽  
Transient Phenomena ◽  
Discharge Valve ◽  
Delivery Pressure ◽  
Cavitation Behavior

In the 1st report, the dynamic behavior of a cavitating centrifugal pump was related to the transient phenomena at the sudden opening/closure of the discharge valve. In this paper, the experimental study was extended to the transient behavior of the cavitating centrifugal pump at rapid starting/stopping of the pump. Unsteady pressures and flowrate were related to time-dependent cavitation behavior in a similar manner as for the rapid operation of the discharge valve. As a result of the present study, pressure fluctuations were found to occur due to water column separation at the sudden stop of the pump similarly to pressure oscillations associated with the sudden closure of the discharge valve. Moreover, the experimental results on the transient behavior at pump startup indicated that the transient fluctuations of delivery pressure and discharge flowrate are caused by oscillating cavitation similarly to the ones occurring at the opening of the discharge valve.

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 Experimental Investigation of Transient Characteristics of a Double Suction Centrifugal Pump System during Starting Period

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4135
Author(s):  
Faye Jin ◽  
Zhifeng Yao ◽  
Duanming Li ◽  
Ruofu Xiao ◽  
Fujun Wang ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Pressure Fluctuations ◽  
Radial Force ◽  
Operating Conditions ◽  
Resonance Phenomenon ◽  
Pump System ◽  
Transient Characteristics ◽  
Water Transportation ◽  
Blade Frequency ◽  
Broadband Frequency

The starting phase for pumps in water transportation pipelines is crucial and has significant transient characteristics which merit further study in order to evaluate the operational stability of the pumping system. This paper presents the results of a study in which the relative steady operating conditions and starting period of a large double-suction centrifugal pump were monitored in real time, including pressure fluctuations, shaft run-out and vibration at the bearing. The transient characteristics of a double-suction centrifugal pump under different operating conditions have been analyzed using fast Fourier transform (FFT) and continuous wavelet transform (CWT). Results indicate broadband frequency components within the spectrum of pressure fluctuations in the volute casing under all test conditions, and the central frequency of the broadband frequency gradually decreases as flow rate increases and approaches the blade frequency, which is the primary reason for an increase in blade-frequency amplitude. This may produce a vibration frequency that is similar to the natural frequency of a certain part of the double-suction centrifugal pump during the starting period, which causes the resonance phenomenon. The radial force is also large during the starting period, which causes eccentric wear of the seal ring at the impeller inlet.

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