Low Specific Speed Centrifugal Pump Research Articles

Cavitation mitigation via curvilinear barriers in centrifugal pump

Cavitation is a significant problem in hydraulic machinery that leads to the deterioration of hydraulic performance, material damage, and flow instability. While current methods partially address cavitation instability, there is a lack of comprehensive understanding of the control mechanisms. This study focuses on controlling cavitation flow instability in a centrifugal pump by proposing an active method using obstacles on the blade's surface. A low-specific speed centrifugal pump was chosen as the research object, and a three-dimensional unsteady full-flow channel numerical simulation was conducted. The findings indicate that in the absence of cavitation, the wake vortex induced by obstacles increases energy loss in the centrifugal pump, resulting in a slight drop in efficiency. However, when cavitation occurs, the obstacles effectively improve the flow field, reduce the vortex strength near the back of the blade in the flow channel, and significantly reduce the growth rate of cavitation volume. This reduction is observed in both the cavitation volume and its first derivative. Thus, the obstacles optimize the flow structure, reduce vortex strength, and slow the growth rate of cavitation. The main control mechanism involves inducing high-pressure waves to collapse cavities and improving flow transition characteristics. To solve the inverse problem of cavitation control with obstacles inside a centrifugal pump, dimensionless geometric parameters are studied to determine better suppression effects.

Numerical investigation of cavitation suppression of centrifugal pump based on the bionic humpback whale blade

Abstract Cavitation is inevitable during the operation of centrifugal pumps, it leads to the decrease in head and efficiency, and induced pressure fluctuation. This paper takes low specific speed centrifugal pump as the research object, a method of inhibiting cavitation by bionic humpback whale blade is proposed, the SST turbulence model is used to numerically study the whole flow passage of centrifugal pump. Comparative analysis of the cavitation characteristic curves under design conditions, the effects of bionic blades on water vapour volume fraction distribution, static pressure distribution, turbulent kinetic energy, vorticity field, streamline were investigated, the variation laws of cavitation morphology under different cavitation numbers is clarified. The research provides theoretical support for improving the cavitation performance and operation stability of centrifugal pump.

Investigation of internal flow characteristics in volute with varying inlet widths for low specific speed centrifugal pumps

Investigation of internal flow characteristics in volute with varying inlet widths for low specific speed centrifugal pumps

Numerical investigation of axial force of a centrifugal pump in the reverse mode

This paper numerically investigates the hydraulic performance and axial force of a low specific speed centrifugal pump in the turbine mode using the k - ω SST model. Numerical results are validated against the experimental data in the literature and a good agreement is observed. Results show that the rotation factor increases by flowrate, since the head, which is directly proportional to the transferred circumferential momentum, increases by the flowrate in the turbine mode. Moreover, values of rotation factors on both sides varies in radial direction due to geometrical parameters and, they reduce where larger axial gaps are present. Additionally, the pressure distributions on the hub and shroud sides are correlated with rotation factors on these areas. Interestingly, the axial position of the impeller plays an important role in the axial force of the PAT. By applying impeller movement of 5 mm from its original position, the point of zero axial force has shifted to higher flowrates and the maximum axial force is reduced 50%. Finally, with 10 mm movement of the impeller, the axial force exhibits distinct behavior so that its direction is preserved and, the returned magnitude is almost constant in the working range by 60% decrease in the maximum axial force.

Transient Hydraulic Performance of a Prototype Pump during Starting and Stopping Periods

In order to meet different operational requirements, existing low specific speed centrifugal pumps may have to be run at high speeds. Therefore, it is crucial to understand the transient performance of such centrifugal pumps during high speed starting and stopping. However, there are currently no experiments on the starting and stopping of low specific speed centrifugal pumps. In this paper, transient hydraulic performance experiments during starting and stopping had been carried out on an atypical open impeller centrifugal pump with a rated flow rate of 6 m3/h using an updated test rig. The correlation of speed, flow, head and shaft power with time was obtained for four flow ratios of 0.353, 1.022, 1.654 and 2.343 operating conditions. It was found that the fluctuation of the shaft power curve was the strongest during the starting process, and there was a significant impact phenomenon. The corresponding impact shaft power from small to large flow rates were 0.167 kW, 0.409 kW, 0.234 kW and 0.215 kW, and the shaft power impact phenomenon was the most obvious under rated operating conditions. During the stopping process, the speed, flow rate and head all remain stable for a small period of time, and the time required to decrease to 0 is longer than the time required to reach a stable state during starting. During stopping, the shaft power will instantly decrease, accompanied by varying degrees of fluctuations.

Analyses of energy loss characteristics of a low-specific speed centrifugal pump as turbines (PATs) based on entropy generation analysis model

Analyses of energy loss characteristics of a low-specific speed centrifugal pump as turbines (PATs) based on entropy generation analysis model

RESEARCH ON THE FLUID-INDUCED EXCITATION CHARACTERISTICS OF THE CENTRIFUGAL PUMP CONSIDERING THE COMPOUND WHIRL EFFECT

In order to study the correlation mechanism between the flow characteristics and the fluid-induced force under the compound whirl motion in the centrifugal pump, the RNG k-ε model is selected in this paper to simulate a low specific speed centrifugal pump with impeller eccentricity based on the N-S equation. The changes of fluid-induced force with impeller eccentricity and the unsteady flow characteristics of the internal flow field of centrifugal pump under different flow conditions and rotation speeds are investigated, and the relationship between the fluid-induced force of the impeller and the internal flow field characteristics is discussed. The results show that the trend of fluid-induced force and the pressure coefficient is similar. When the rotation speed changes and when the flow is similar, the pressure coefficient under different rotation speeds almost coincides. With the increase of impeller speed and impeller eccentricity, the dynamic and static interferences between the impeller and the volute tongue are more significant, the uneven distribution of the pressure around the impeller makes the internal flow of centrifugal pump more disordered and increases the fluid-induced force near the volute tongue. The research results can provide important reference value for accurately grasping the internal flow excitation principle of the centrifugal pump.

A precisive calculation method of volumetric and hydraulic efficiency of centrifugal pumps

This paper proposes a new method to calculate the volumetric efficiency and hydraulic efficiency of centrifugal pumps based on the principle of energy balance. Two efficiencies are calculated by means of a low specific speed centrifugal pump handling media with different viscosities at best efficiency points and are compared with those of two existing methods. The results manifest that the definition of two efficiencies in the present paper is more precisive and sensitive to the change of liquid viscosity.

A Compressible, Coupled Three-Dimensional/One-Dimensional Flow Solution Method for the Seamless Simulation of Centrifugal Pumps and Their Piping

Abstract A compressible finite volume Navier–Stokes flow solver is coupled to a method of characteristics for the seamless turbulent flow simulation of entire pump systems. For the pump, three-dimensional (3D) simulations including cavitating flow conditions are performed, and the piping is treated one-dimensional (1D) by a method of characteristics. Thus, classical boundary conditions at the suction and pressure pipe of the 3D computational domain of the pump are substituted by a two-way coupled 1D piping simulation method. Particular emphasis has been placed on the non-reflecting properties of the 3D–1D coupling interface. For validation, in-house experiments are performed on a low specific speed centrifugal pump in a closed-loop facility. For cavitating flow conditions, excitation on the pump's pressure side by rotor–stator interaction is enhanced over a broad frequency spectrum due to collapsing voids. The suction side piping is shielded by void regions within the blading from the excitation on the pump's pressure side, leading to an acoustic decoupling of the suction side. These experimental observations are reproduced by the new seamless simulation method. In particular, the measured pressure amplitudes are well reproduced for a broad frequency spectrum, at several piping positions, and for a variation of the flow rate and the cavitation intensity. Remaining deviations to experimental data are traced back to the omission of structural compliance and uncertainties regarding the pressure side piping modeling, which will be addressed in future studies.

Parameter Optimization of Centrifugal Pump Splitter Blades with Artificial Fish Swarm Algorithm

Low specific speed centrifugal pumps typically suffer from low efficiency and severe backflow; adding optimally structured splitter blades can play a role. In this paper, the distribution of pressure and velocity in the flow channel is analyzed using CFD simulation for a low specific speed centrifugal pump. The geometric parameters of the splitter blade are optimized using an orthogonal test and an artificial fish swarm algorithm; then the optimal splitter blade structure is obtained. Results showed that the splitter blade not only effectively solves the backflow of the flow channel and compresses the range of the trailing vortex, but it also alleviates the cavitation at the inlet of the main blade. When considering the best head, the order of influence of each factor is: Splitter blade thickness > Splitter blade inlet diameter > Splitter blade inlet width. At this time, the thickness of the splitter blade is 4.5 mm, splitter blade inlet diameter is 155 mm (0.775) and Splitter blade inlet width is 23 mm. Through the closed pump experimental system, it is confirmed that hydraulic performance has been improved.

Performance Optimization of Slotted Blades for Low-Specific Speed Centrifugal Pumps

Centrifugal pumps are widely used for the transport of fluids, but low-specific-speed centrifugal pumps widely have problems with serious backflow and low efficiency. In this paper, a low-specific-speed centrifugal pump with a specific speed of 55 is used as a research object. By combining numerical simulation and orthogonal experiment, the pressure distribution and velocity distribution of the flow channel are analyzed, the priority of each geometric factor for slits on pump performance is determined, the geometric parameter structure of the slotted blade is optimized by entropy weight on TOPSIS, the optimal impeller slit solution is obtained. The results show that with a balance of head and efficiency, the order of influence of the factors is: slit center width b > diameter of slit D > shrinkage ratio of slit f > depth of slit h > deflection angle of slit β . The optimal combination of slit geometry parameters is: slit center width is 3 m m , diameter of the slit is 200 m m , shrinkage ratio of the slit is 0.5, depth of the slit is 6 m m , and the deflection angle of the slit is 20°. Through ANSYS FLUENT simulation and experiment of closed pump experiment system, confirmed that hydraulic performance is improved.

Multi-Objective Optimization Design of Low Specific Speed Centrifugal Pumps Based on Genetic Algorithm

Multi-Objective Optimization Design of Low Specific Speed Centrifugal Pumps Based on Genetic Algorithm

Study on external performance and internal flow characteristics in a centrifugal pump under different degrees of cavitation

Cavitation as a form of unsteady flow within centrifugal pumps can cause the reduced performance of pumps, disordered internal flow regimes, and flow loss. The present criterion used for determining the occurrence of cavitation is a 3% head drop. However, in most cases, pump cavitation already occurs with less than a 1%–2% head drop due to significant changes in the internal flow status. To examine changing patterns in internal flow characteristics as the degree of cavitation deepens in the early stage of cavitation in centrifugal pumps when the head curve does not show significant fluctuation, this paper focuses on a low specific speed centrifugal pump to analyze distributions of total internal pressure, speed, bubble volume, vortex structure, and entropy generation across different degrees of cavitation and obtain internal flow characteristics and flow loss patterns of pumps, with an aim of providing preferences for anti-cavitation hydraulic design of centrifugal pumps.

Numerical Analysis and Experimental Study of Unsteady Flow Characteristics in an Ultra-Low Specific Speed Centrifugal Pump

Low specific speed centrifugal pumps are widely used in urban water supply, agricultural irrigation, petrochemical and other fields due to their small flow rate and high head. Therefore, the study of unsteady flow characteristics plays a vital role in its safe and stable operation. In this paper, numerical simulation and experimental methods are used to explore the unsteady performance of the pump. The results show that the fluctuations of the external characteristic such as head, shaft power and energy loss are due to the periodic disturbance of the flow field of pump. But the transient performance of shaft power and head shows different changing trends due to different influencing factors. In this paper, the transient process of hydraulic performance is divided into three stages according to the causes and characteristics of hydraulic fluctuations. Most of the hydraulic losses occur inside the impeller, so the impeller flow field determines the level of time average hydraulic performance. Although the hydraulic loss of the spiral case is small, it is greatly affected by the rotor-stator interaction, which affects the strength of the hydraulic fluctuation. This study is of great significance to the mechanism of rotor-stator interaction and the stable operation of low specific speed centrifugal pumps.

Effects of Blade Suction Side Modification on Internal Flow Characteristics and Hydraulic Performance in a PIV Experimental Centrifugal Pump

In this paper, the effects of blade trailing edge (TE) profile modification of the suction side on the internal flow and hydraulic performance in a low-specific speed centrifugal pump are investigated through particle image velocimetry (PIV) analysis. Three impellers with different blade trailing edge profiles named original trailing edge (OTE), arc trailing edge 1 (ATE1), and arc trailing edge 2 (ATE2) are designed for PIV experiments. Results show that blade trailing edge modification of the suction side can significantly change the flow pattern, affecting the hydraulic performance of the model pumps. There is a definite counterclockwise backflow vortex near the suction side of OTE at deep-low flow rate, resulting in a decrease in the uniformity of the flow field at the outlet and the hydraulic performance. ATE1 with a reasonable larger blade outlet angle has the best flow field, and the head and efficiency are increased by about 1.2% and 8%, respectively under the same working condition. The hydraulic performance of ATE2 with the blade outlet angle of 59° is better than that of OTE under low flow rate, but it is less than that of OTE under high flow rate due to the streamline deviation generated on the pressure side. Meanwhile, the energy conversion abilities of the modified model pumps are evaluated by slip factor and the deviation degree of the nominalized local Euler head distribution (NLEHD). Since there is no definite counterclockwise backflow vortex at the outlet after modification, the slip factor of ATEs increases and the energy conversion ability is enhanced. Moreover, the jet-wake phenomenon of ATEs is weakened, and the local Euler head (LEH) increases near the outlet, decreasing the deviation degree of the NLEHD to obtain better energy conversion ability.

Optimization design of hump phenomenon of low specific speed centrifugal pump based on CFD and orthogonal test

Aiming to eliminate the hump phenomenon in a low specific speed centrifugal pump, its structural parameters were optimized using the computational fluid dynamics method. Based on the k - varepsilon turbulence model, a 3D steady analysis of the internal flow field was carried out. The L_{9} left( {3^{4} } right) orthogonal table was established, and four structural parameters, including the impeller outlet diameter, impeller outlet width, number of blades, and blade outlet angle, were selected as influencing factors. Nine orthogonal test schemes were developed and the results were analyzed through the weight matrix analysis method, obtaining the weight of the selected factors on the test results. The optimal scheme was selected according to the weight and the weight matrix analysis results have shown that the impeller outlet width had the dominant influence on the head, shaft power, and efficiency. Further, the blade number was the main influencing factor for shaft power and efficiency. The centrifugal pump flow control test bench was built to carry out the numerical simulation and test all the prototype and optimization pump indexes. Through the external characteristic test, it can be seen that the beta_{2} Z^{0.773} of the optimized pump is 87.889, which is 24.89% lower than that of the prototype pump, which effectively optimizes the hump phenomenon of the centrifugal pump. The experimental results have shown that in underrated working conditions, the working performance of the optimized pump was improved significantly. The head size was reduced by 1.424%, and the efficiency was increased by 7.896%. By optimizing the structural pump parameters, its jet-wake hydraulic loss was reduced, and the head curve hump phenomenon was effectively eliminated. All the performance indexes of the optimized pump were higher than those of the prototype, verifying both the accuracy and reliability of the orthogonal test and weight matrix analysis method. Finally, obtained results provide a reference for the structural design of high-performance centrifugal pumps.

Numerical Simulation of Cavitation Flow in a Low Specific-Speed Centrifugal Pump with Different Diameters of Balance Holes

In order to study the influence of a balance hole’s diameter on the cavitation performance of low specific-speed centrifugal pumps, a centrifugal pump with a specific speed of 0.301 was selected as the research object. The pump’s cavitation performance, distribution of cavitation vapor in the impeller, and axial force on the impeller were studied with the change in diameters of balance holes. The results show that with the increase in the diameter of balance holes, the cavitation number σ3% of the low specific-speed centrifugal pump became small, the pressure in the mechanical seal cavity dropped gradually, and the flow velocity in balance holes was reduced. As cavitation occurred in the impeller, the diameter of balance holes not only affected the absolute value of the axial force but also affected the direction of the axial force.

Numerical simulation of complex flow structures and pressure fluctuation at rotating stall conditions within a centrifugal pump

AbstractRotating stall contributes to global oscillation vibration problems, accompanied by noise and possible turbomachinery damage. This study with special emphasis on the vaned diffuser investigates the unsteady pressure interaction with the stall within the pump. A low specific speed centrifugal pump (ns = 69), fitted with a vaned diffuser is modeled and studied. The model pump performance curve shows the characteristic positive slope at 30% of the best efficiency point flow rate; 1.0 ΦΝ which is attributed to the stall phenomena. A finite volume method is employed with unsteady computations initialized utilizing shear stress transport k‐ω before proceeding with DDES. Pressure fluctuation and velocity magnitude normalized values are used to investigate the evolution of stall cell generation. The root mean square (RMS) values and normalized pressure (Cp) values are elicited to gain insight into pressure pulsation within the flow domain. The distinguished “starfish” shape is observed for monitor points md1 to md20, with the RMS trend decreasing with increasing flow rate from the pump shut off. Although in the vaned diffuser flow channel, an increase in pressure fluctuation along the flow channel toward the trailing edge is observed, the vaned diffuser channel shows a similar trend. The stall cell propagates at a speed of ΩRS = 0.078 at 0.2 ΦΝ, while at 0.1 ΦΝ propagates at a speed of ΩRS = 0.087; the stall speed tends to increase approaching pump shut off. Three distinguishable stall channels are observed from the flow structure for a five vaned diffuser; entering the stall, stalled, and stall recovery stages, within the flow channels.

Inverse Design and Optimization of Low Specific Speed Centrifugal Pump Blade Based on Adaptive POD Hybrid Model

To improve the prediction accuracy of the surrogate model and reduce the calculation cost for hydraulic optimization design of centrifugal pump impeller, an inverse design and optimization method based on adaptive proper orthogonal decomposition (APOD) hybrid model was proposed. Initial samples were designed by perturbing blade control parameters of the original model. The samples were classified using the K-means clustering algorithm, and the adaptive samples were selected according to the category of the objective sample. The snapshot set is composed of blade shape parameters and the CFD flow field data in impeller, which is decomposed into a linear combination of orthogonal bases by the proper orthogonal decomposition (POD) method to predict the objective parameters. According to the objective load distribution, the low specific speed centrifugal pump was inversely designed by using the APOD model, and its initial blade was obtained. And then, the flow field corresponding to disturbed blade shape was predicted using the APOD method, so as to evaluate the gradient of the objective function to design variables. Finally, the initial blade was optimized by the gradient descent method. The results show that the APOD hybrid model method can be employed to accomplish the blade inverse design and the flow field prediction in the optimization design of centrifugal impeller, which significantly reduces the numerical calculation cost and improves the accuracy of the flow field prediction.

Study on fluid dynamic characteristics of a low specific speed centrifugal pump with emphasis on trimming operations

In the present investigation, the fluid dynamic characteristics of a narrow channel centrifugal pump are studied using numerical simulations with special emphasis on pump trimming operations. The trimming operations at optimized rate, reduce the pressure fluctuations and hydraulic noise in pumps, but at the cost of pump performance characteristics. This has been extensively studied by the researchers in the past; however, the efficacy of trimming operations on industrial pumps with narrow channel passage impellers is to be explored. A low specific speed pump with narrow channel impeller passage and radial discharge volute (M1) with specific speed of 14.7 is considered for the present investigation. Detached Eddy Simulation (DES) is used in transient simulations and Fast Fourier Transform (FFT) is used to understand the pressure fluctuations and hydraulic noise at the Blade Pass Frequency (BPF) and its harmonics. The pressure fluctuation behavior along the impeller periphery is monitored at 30 equidistant probes and 7 probes covering the volute tongue. These results are compared with the similar study for impeller with oblique trimming of 30° (M2) and impeller oblique trimming along with volute trimming (M3). The flow behavior in M1 is dominated by a Jet-wake flow in the impeller passage which acts as a primary source of flow non-uniformity. The resulting non-uniform flow on the impeller periphery interacting with the volute tongue causes vortex shedding behind the volute tongue, subsequently leading to discharge recirculation in the impeller. The coefficient of pressure fluctuations near volute tongue at BPF is reduced by 10.3% in M2, whereas it is enhanced by 24% in M3 relative to M1. The enhanced vortex shedding behind the volute tongue in addition to the vortex train along the impeller periphery causes rise of the pressure fluctuations in M3.