Net Positive Suction Head Research Articles

Experimental and numerical study on cavitation pulsating pressure of water-jet propulsion axial-flow pump.

Cavitation may occur in water-jet pump during operation of water-jet propulsion vessel, and once cavitation occurs, the tip clearance pulsating pressure of the impeller may be intensified, resulting in increased vibration of the water-jet propulsion unit. In this paper, the cavitation pulsating pressure characteristics at different positions in the pump are studied by experiment and numerical simulation, and the pulsating pressure characteristics in tip clearance are mainly researched. Based on Star-CCM+ commercial software, unsteady Reynolds-averaged Navier-Stokes equations(RANS) numerical simulation is carried out, and the feasibility of the numerical simulation method is verified by uncertainty analysis. The results show that the cavitation pulsating pressure near the leading edge of the impeller in the tip clearance is the largest. The variation of the tip clearance pulsating pressure with the intensification of cavitation is studied by numerical simulation, and its mechanism is revealed. A dimensionless coefficient of net positive suction head (CNPSH) is proposed, and the study shows that the cavitation pulsation pressure coefficients of pumps of different scales are equal when the working conditions are similar and the CNPSH are equal, which indicates that the cavitation pulsating pressure performance of full scale pump can be predicted by model scale. It is of great significance to evaluate the vibration performance of the full scale water-jet propulsion.

Cavitation state recognition method of centrifugal pump based on multi-dimensional feature fusion and convolutional gate recurrent unit

The rapid and accurate recognition of cavitation in centrifugal pumps has become essential for improving production efficiency and ensuring machinery longevity. To address the limitations of existing methods in terms of applicability, accuracy, and efficiency, a new method based on multi-dimensional feature fusion and convolutional gate recurrent unit (MCGN) was proposed. Experimental monitoring of cavitation of centrifugal pumps was conducted. Five signals at different water temperatures and operating frequencies were collected. Key modulating features were extracted by time-frequency analysis and principal component analysis. The multi-dimensional features are fused by one and two dimensional convolutional neural networks. The cavitation state label was used to label the sample set by cavitation number, net positive suction head, and cavitation evolution images captured by high-speed cameras. Finally, the neural network based on the convolutional gate recurrent unit was used to classify the cavitation state of the centrifugal pump. The experimental results demonstrate that the proposed method achieves recognition accuracies exceeding 98% for vibration signals, noise signals, outlet pressure pulsation signals, and torque signals. Compared with the short-time Fourier transform-autoencoder model, MCGN model can improve the recognition accuracy by 4.03%, computation efficiency by 20%, and loss by 87%. These advances underscore the potential of the method in monitoring and maintenance practices for centrifugal pumps.

Prediction of cavitation using machine learning techniques on centrifugal pump

Abstract When the local static pressure drops below the fluid’s vapour pressure at that particular temperature, a dynamic process known as cavitation takes place in the liquid. Due to cavitation, the performance (total head and flow rate) of the pump will deteriorate, and hence the vibration and noise will develop. Both the performance and cavitation investigations are carried out for a low-specific-speed pump as per the testing standards. The results obtained during cavitation studies are extracted to train the machine learning algorithms. The flow rate, speed, torque, suction head, and delivery head are considered as input variables for machine learning, with total head, Net Positive Suction Head (NPSH), efficiency, and noise magnitude being output variables. The current studies employ four machine learning techniques: random forest, support vector machines, extreme gradient boosting, and linear regression. In the analysis, notable performance was observed for the random forest and extreme gradient boosting algorithms among others consistently demonstrated superior predictive capabilities for the output parameters of the pumps. For linear regression, random forest, and extreme gradient boosting, the coefficient correlation values are around one for all output parameters except for noise. Similar observation is depicted for coefficient of determination and normalized root mean squared error. These ensure the level of noise during cavitation is very dynamic. These findings will enable the pump user to incorporate AI techniques for the diagnosis of centrifugal pump operation with reference to the nominal flow rate (best efficiency flow). Through this technology, preventive and predictive maintenance of pumps can be adapted with less downtime in process industries, power plants, chemical industries, oil and gas refineries, and so on.

Study on the transient cavitation characteristics in an axial flow tandem pump during the rapid starting period

Abstract In axial flow pump systems constrained by limited internal space, the advantages of axial flow tandem pumps are high space utilization, strong power capacity, and great thrust. The onset of cavitation during the rapid starting period poses a classic issue for tandem axial flow pumps, resulting in issues like noise, vibration, cavitation breakdown, and material damage. This article aims to investigate the transient cavitation characteristics of each flow passage component of an axial flow tandem pump during the rapid starting period by numerical simulation method. It is compared that the evolution laws of the cavity of each flow passage component. The evolution of the cavity in all flow passage components is strongly correlated with the flow rate change rate in each stage of the rapid starting period. Among all flow passage components, the first impeller firstly experiences cavitation, and its cavitation severity is also the most severe. The Effective Net Positive Suction Head (NPSHa ) can reduce the influence of transient effects on cavity prediction and better characterize the details of the cavity evolution in different impellers than the cavitation number σ during the rapid starting period. Meanwhile, The NPSHa of the second impeller inlet is always higher than that of the first impeller inlet, indicating superior cavitation performance for the second impeller.

Exploring cavitation dynamics and noise reduction in hydraulic machinery with bionic leading edge impeller

Cavitation and induced noise are common issues in the operation of mixed-flow pumps, affecting their stability. Studying these phenomena is of both academic and engineering interest. Previous research has mainly focused on modifying the impeller blade profile or optimizing the pump structure to reduce cavitation and noise. In this paper, we apply a bionic design to the mixed-flow pump impeller by mimicking the natural shape of a humpback whale's pectoral fin on the leading edge of the blade. We compare the cavitation suppression and noise reduction effects of this design with those of a conventional mixed-flow pump. Unsteady flow calculations for the original pump at different flow rates revealed that at its rated speed, increasing flow rates led to lower pressure in the low-pressure region on the suction surface of the impeller, expanding the cavitation-prone area. By applying the bionic design, we studied the unsteady cavitation flow and its induced noise. Results showed that the impeller and guide vane experienced larger pressure pulsations at the rotation frequency and its multiples. The bionic modification increased the cavitation initiation speed and reduced the cavity volume within the runner. With an NPSH (net positive suction head) of 6.76, the void volume in the bionic pump was only 79% of that in the original pump, and the head increased by 16%. Additionally, the bionic design reduced the maximum far-field sound pressure level by 12.5%, achieving significant noise reduction. This study demonstrates that the bionic design effectively controls dynamic flow separation, reduces flow-induced noise, and enhances the mixed-flow pump's performance. These findings have important theoretical and practical implications for optimizing mixed-flow pump design, improving energy efficiency, and reducing noise.

A cavitation performance prediction method for pumps PART3 feasible for axial-flow reactor coolant pump

This study introduces a novel method to enhance the prediction of cavitation performance in axial flow reactor coolant pumps. Utilizing computational fluid dynamics (CFD), the paper examines the internal flow characteristics and establishes a relationship between minimum pressure, low-pressure isosurface area, and net positive suction head (NPSH). A key finding is that the pressure isosurface area ratio to blade area (Rs) is crucial for cavitation prediction. The study’s method was validated under design conditions with an initial cavitation prediction hypothesis. It was determined that at a flow rate of 0.2912 m3/s and a rotational speed of 1485r/min, the pump’s critical cavitaion performance NPSHc is 4.52 m, with a corresponding low-pressure isosurface pressure of 57117.6 Pa. The current low-pressure isosurface area is 0.00581849 m2, and the blade area is 0.13452 m2, yielding an Rs of 4.325 %. The study reveals a linear relationship between the pressure isosurface area and NPSHa when NPSHa is below a certain threshold, suggesting that this area can predict cavitation performance. This method is significant for optimizing the design and cavitation performance of axial flow reactor coolant pumps.

Machine Learning-Based Prediction of NPSH, Noise, and Vibration Levels in Radial Pumps Under Cavitation Conditions

Cavitation, a physical phenomenon that detrimentally affects pump performance and reduces pump life, can cause wear on pump elements. Various engineering methods have been developed to identify the initiation and full development of the cavitation process. One such method is the determination of the net positive suction head (NPSH) through a 3% decrease in total head (Hm) at a constant flow rate. In radial pumps, commonly used in agricultural irrigation and industry, cavitation conditions result in a sudden drop in the Hm-Q curve, making it challenging to detect the 3% Hm value drop. This study differs from others in the literature by modelling NPSH, noise, and vibration levels using three machine learning models, specifically artificial neural networks (ANN), support vector machines (SVM), and decision tree regression (DTR). The best-performing model predicts NPSH, noise, and vibration levels corresponding to a 3% decrease in Hm level. The present study determined the NPSH values of a horizontal shaft centrifugal pump at different flow rates and constant operating speed, and the vibration and noise levels were measured for these NPSH values. For each of the NPSH, noise, and vibration levels, ANN, SVM and DTR models were created. The performances of these models were evaluated using criteria such as root mean squared error (RMSE), Mean Absolute Error (MAE) and mean absolute percentage error (MAPE). In addition, Taylor and error box diagrams were created. The ANN model and DTR yielded high accuracy predictions for NPSH values (R2 = 0.86 and R2 = 0.8, respectively). The ANN model provided the best prediction performance for noise and vibration levels. By entering the level of 3% drop in the Hm value of the pump as external data input to the ANN model, NPSH3, noise, and vibration levels were determined. The ANN models can be effectively employed to determine NPSH3, noise, and vibration levels, particularly in radial flow pumps, where detecting 3% reductions in manometric height value is challenging.

Resizing of Irrigation Pumps Used for Heap Leaching in a Mine: Case of SOMAÏR

The aim of this study is the analysis and resizing of irrigation pumps used in heap leaching at the Mines de l'Aır company. This company is located in the Arlit department in the Agadez region of Niger. This work essentially consisted of checking the current pumps, integrating the new parameters and choosing the right pumps, either by respecting the current standard or by proposing other types of more efficient pumps. The study revealed that for the 3rd stage pumping circuit, the Total Head (HMT) value of 33.58 m is lower than that of the pumps, which is 34.03 m. This pump sends the fluid to the desired heap height with a pressure of 0.5 bar, whereas the desired pressure for watering is around 2 bar. The result: a drop in uranium juice production. The pump does not exhibit cavitation, as the Net Positive Suction Head (NPSHD) is equal to 4.71 m, a value that far exceeds the NPSHr , which is equal to 1.44 m. Given that at 1485 rpm the pump is unable to deliver a pressure of 6 bar with the valve closed, we can say that the pump has lost its performance. By the 3rd stage, the HMT of the circuit is equal to that of the pump, so the pump will still be able to deliver the fluid to the piles, but at a very low pressure, and even if both pumps are switched on simultaneously, the flow rate will not exceed 150 m3 /h. This means that irrigation will be very poor, resulting in mediocre uranium juice production. With a pump efficiency of 61.98%, we can say that the pump is operating under optimum conditions and does not suffer from cavitation, as the NPSHD is well above the NPSHr . For the 4th stage circuit, the CPKN 100-404 pump driven at 1650 rpm gives a flow rate of 175 m3 /h and a head of 57.91 M.C.E. The MegaCPK 125-80-380 pump driven at 1750 rpm gives a flow rate of 190 m3 /h and a head of 60.28 M.C.E. The CPKN 150-440 pump, driven at 1450 rpm, operates at 230 m3 /h and 67.55 M.C.E. The MegaCPK 150-125-380 pump, driven at 1750 rpm, delivers 250 m3 /h and a head of 71.71 M.C.E.

Exploring a new criterion to determine the onset of cavitation in centrifugal pumps from energy-saving standpoint; experimental and numerical investigation

This paper proposes a new criterion to determine the cavitation initiation in centrifugal pumps. Because of the importance of saving energy, and the need for specifying a margin for the required net positive suction head (NPSHr) in all centrifugal pumps, a new criterion based on dropping three percent in efficiency (NPSHr,η) was investigated. Extensive experimental and numerical studies were undertaken to assess the effectiveness of the novel criterion from the energy-saving standpoint and its margin compared to the conventional one (NPSHr,Ht). A test bench was employed to conduct numerous experiments on five single-stage centrifugal pumps, generating comprehensive head-drop and efficiency-drop curves under part-load, designed, and over-load conditions. Additionally, simulations were carried out using CFD, employing an appropriate turbulence model and the ZGB cavitation model. Subsequently, dropping curves of total head, hydraulic efficiency, and the torque-rise curve against available NPSH were extracted. Analysis of these simulations revealed that NPSHr,η is consistently higher than NPSHr,Ht. A three-percent total head-drop diminishes the efficiency by an average of 6.04%, ranging from 4.79% to 8.92% depending on the specific case. Using NPSHr,η provides enough distance from the NPSHr,Ht without any need to specify a margin, and a huge amount of energy can be saved annually.

Investigation of cavitation characteristics in an aircraft centrifugal fuel pump

Cavitation is a classic gas–liquid two-phase flow phenomenon that needs to be restricted for the hydraulic performance enhancement of centrifugal pumps. However, due to the particularity of fuel mediums and rigorous aviation conditions, the characteristics of cavitation occurring in aircraft centrifugal fuel pumps have not been elaborated. In this research, cavitation characteristics in an aircraft centrifugal fuel pump with a high rotational speed of 14,000 rpm were investigated by considering the influence of the flow rate ranging from 0.2Qd to 1.2Qd and the fuel temperature ranging from 20 °C to 100 °C. An experiment for testing the hydraulic performance of an aircraft centrifugal fuel pump was built, and a corresponding numerical simulation of gas–liquid two-phase flow was employed. The distributions of the pressure, streamlines, and turbulence kinetic energy in the centrifugal pump for different flow rates and fuel temperatures were comparatively analyzed. The net positive suction head available (NPSHa) was defined to represent the cavitation degree, and the net positive suction head required (NPSHr) was introduced to characterize the critical cavitation occurrence. It was also found that a large area of cavitation bubbles was generated in the inducer and that this area grew to block the flow channel of the impeller when the NPSHa was close to or lower than the NPSHr, which was the cavitation mechanism of hydraulic performance degradation. Additionally, the developments of the NPSHr with the flow rate and fuel temperature were determined adequately using natural exponential curve fitting. It was deduced that the occurrence of cavitation was more sensitive to higher flow rates, especially when the flow rate was higher than the designed flow rate. The effect of fuel temperature variations should also be considered for the long-time high-speed operation of centrifugal fuel pumps in the aerospace industry.

Investigation of cavitation evolvement in a pump inducer by proper orthogonal decomposition analysis of video images

The aim of this study is to develop a contour extraction method for the investigation of the temporal and spatial characteristics of cavitation evolution in high-speed inducers. Cavitation experiments were conducted, and corresponding snapshots were captured using a high-speed camera subsequently. The raw images were processed while using threshold value filtering techniques to extract only relevant bubble information. Proper orthogonal decomposition was employed to explore the evolving characteristics in a quantitative manner. Results show that the cavitation evolution process is an unsteady process when viewed from the side. In high net positive suction head (NPSH) environments, multiple small-scale spatial modals contribute significantly to the effective proportion of the cavitation structure. The attached sheet cavitation exists in the blade edge which is the main embodiment of cavitation area evolvement. Under low NPSH conditions, the primary flow feature can be reflected by a low-mode flow pattern, associated with the inducer’s rotation effect. The evolving regulation of cavitation area in developed stage is closely submitted to the trigonometric function. And the exhibited spatial coefficient exposes the hidden reflux vortex feature. The proposed image separation techniques enable the quantification of morphological features, which can provide technical details for the digital design of inducers.

Effect of Cavitating Hydraulic Elements on Pump Characteristics

The effective and reliable performance of any pump can be significantly impacted by the piping system design. One of the essential points is the pump suction pipe. Poor design and dimension of the suction piping can lead to cavitation in the pump which affects its head and efficiency. The primary objective is to reduce the hydraulic losses of the suction piping in order to maintain a Net Positive Suction Head required by the pump. Suction piping is recommended to be short and straight, and branch connections, valves and elbows should be avoided, which is not always possible. In addition, cavitation can occur in the actual hydraulic elements installed on the pump suction. This work is focused on the investigation of cavitating hydraulic element in the suction pipe on the pump performance. A converging-diverging nozzle with a circular cross-section was used for this purpose. A straight pipe segment of constant diameter and the same length was used for comparison. Both elements were characterized by the loss coefficient and the cavitation number. Their influence on the pump head and the Net Positive Suction Head Available (NPSHA) was investigated.

Depressurization induced vapor bubble growth in liquid methane during microgravity

Depressurization and re-pressurization maneuvers are used for cryogenic propellants in spacecraft tanks to mitigate the incoming heat flow and to maintain an appropriate net positive suction head (NPSH). A depressurization maneuver can be used to transfer thermal energy from liquid to vapor and thus allow for subcooling of the liquid by a following, quick pressurization. The depressurization will lead to phase change, caused by the superheat relative to the initial saturation conditions, and the following pressurization will subcool the bulk liquid. Phase change will occur at any of the free surfaces of the bulk liquid or at nucleation sites in cavities at a wall. The mechanism which governs phase change at nucleation sites differs from nucleate boiling due to the temperature distribution in the liquid. In this study, we investigate the behavior of a single nucleation site during a depressurization under microgravity. We observed the bubble growth and evaluated the bubble radius with time. A total of five experiments were performed. The thermodynamic conditions are known and therefore can be correlated to the vapor bubble growth behavior. The superheat in the system varies with time, thus simple models are not applicable but can be used to estimate the bubble size. The data can be used as a reference for further analytical or numerical investigations.

DETERMINING OPTIMAL SIMULATION SETTINGS FOR THE CENTRIFUGAL PUMP PARTS OPTIMIZATION PROCESS

This paper explores the optimal simulation settings required by the optimization process of centrifugal canned motor pump parts using the CH 6,3/32-2,2-2 pump as an example. The optimization of centrifugal pump parts is particularly important in order to increase pump characteristics: pump efficiency, net positive suction head, as well as other optimization criteria. The optimal conditions to obtain a geometric model and optimal mesh properties, initial and boundary conditions, solver settings were investigated. The mathematical models used in the simulation were also presented. In conclusion, there have been revealed optimal simulation settings.

Influence of cavitation on energy loss in a side channel pump at different flow rates

Side channel pumps are extremely prone to cavitation, and the internal exchange flow between the impeller and the side channel induces numerous vortical structures that causes significant energy loss. Therefore, it is important to investigate the cavitation characteristics and flow loss in side channel pumps under cavitating conditions. This paper investigates the cavitating flow in a side channel pump using the scale-adaptive simulation turbulence model coupled with the Zwart cavitation model. The development of cavitation in the side channel pump is divided into three stages according to the critical net positive suction head and turning net positive suction head. Stages I, II, and III correspond to the inception of cavitation, development of cavitation, and severe cavitation, respectively. The vortex energy is adopted to analyze the variations in vortices with respect to the available net positive suction head. Entropy production considering viscous dissipation, turbulent dissipation, and the wall effect is used to calculate the irreversible energy loss. However, the energy loss caused by the rotation of vortices cannot be calculated by this method, resulting in large discrepancies between the entropy production and the hydraulic loss calculated by the pressure drop method. The entropy production generated by turbulent dissipation (S2) is found to be dominant in the side channel pump and increases with decreasing flow rate. S2 exhibits different variation trends with respect to the available net positive suction head at different flow rates under severe cavitation. S2 also dominates in the impeller, but the entropy production terms exhibit slight discrepancies in the side channel. The distribution of local entropy production rate further reveals the complicated interaction mechanism between cavitation and entropy production.

Experimental Investigation of Centrifugal Pump Characteristics

The pumps are divided into two main groups as positive displacement namely volumetric pumps and dynamic i.e. centrifugal pumps. Volumetric pumps are generally used to transport hydraulic oils, while centrifugal pumps are used to transport clean or dirty water. Pumps are the tools that are used to move liquid fluids from one place to another in many areas like as cars, industry, construction sites, agriculture, and homes. Therefore, determination of the hydraulic pump’s characteristics under various working conditions, including manometric head, overall efficiency, specific speed, and net positive suction head, is crucial for development, operational limitations, and durability. Experimental investigation is a more realistic method, although it is possible to determine the hydraulic pump characteristics by means of mathematical methods. Therefore, an experimental investigation is performed for the determination of the centrifugal pump characteristics in this study by using an experimental setup. The findings indicate that the hydraulic power given to the water and the electrical power used by the pump both increase up to a particular flow rate and then decline. Additionally, it is found that manometric head of the pump falls even as the overall flow losses rise as the flow rate rises. On the other hand, overall efficiency of the pump enhances at the specific flow rate and then it reduces with the increased flow rate while specific speed of the pump varies about linearly. Moreover, it is finally noticed that the tested centrifugal pump works in cavitations at all flow rates.

Experimental and Numerical Study on Cavitation Effects in Centrifugal Pumps

Experimental and numerical investigations of the centrifugal pump performance at non-cavitating and cavitating flow conditions were carried out in the present study. Experiments were performed by applying a vacuum to a closed-loop system to investigate the effects of the net positive suction head available (NPSHa), flow rate, water temperature and pump speed on the centrifugal pump performance. Accordingly, many of the important parameters concerning cavitation phenomenon were calculated. Also, the noise which is accompanied by cavitation was measured. Numerical analysis was implemented for two phase flow (the water and its vapor) using a 2-D simulation by ANSYS FLUENT software to investigate the internal flow of centrifugal pump under cavitating conditions. It was observed that with decreasing NPSHa, the values of the pump head, flow rate and efficiency initially remain constant, but with further reduction in NPSHa these parameters will decrease. Also, it was found that at 3% head drop the percentage drop of the flow rate is less than 2% whereas the percentage drop of the efficiency is greater than 3%. Numerically, it was noticed that the cavitation regions appear at the leading edge of suction side of the impeller blades which represents the lowest pressure area inside the computational domain of the centrifugal pump.

OPTIMIZATION OF GEOMETRIC PARAMETERS FOR IMPELLER DESIGN IN AN AXIAL FLOW PUMP

This work is mainly concentrated on increasing the efficiency (η) and reducing the Net Positive Suction Head (NPSH) required by optimizing the design through the geometrical parameters involved. Blade thickness, Chord cascade solidity, chord angle and hub angle are the geometric variables evaluated. In order to establish the relation between the geometrical parameters and the objective functions (η and NPSH), a statistical approach in the form of ANOVA and RSM is used and the DOE is performed using Taguchi method. The data for the geometrical parameters were selected based on the technical values commonly used in the present impeller design. The values of objective functions for the analysis were taken from the calculations done using simulation results using appropriate equations. The effect of geometrical parameters on the objective functions is analysed and the optimization of parameters is carried out using RSM in Minitab software

Research of the vibration induced by cavitation in a centrifugal pump under part load condition

Cavitation and the corresponding induced vibration characteristics in a centrifugal pump under part load (0.4Qd, Qd is rated flow) conditions were investigated by combining numerical simulation and experimental analysis to determine the internal flow characteristics and vibration signals under different cavitation conditions. Under part load conditions, cavitation is initiated at the inlet of blades close to the tongue. Expansion of a low-pressure region increases the size of vortex in the flow passages, which increases the severity of the flow instability in the pump during severe cavitation. As cavitation develops, the random generation and rapid collapse of cavitation bubbles produce unstable vibration of the pump system. The high-frequency and broadband pulsation of vibrations distributed in the frequency band of 4–10 kHz can be regarded as typical signals induced by cavitation in the pump at 0.4Qd. The net positive suction head available of the cavitation incipient point is determined to be 9 m at 0.4Qd. The rotor–stator interaction between the impeller and volute affects the vibration signals at individual measurement points, which exhibit clear shaft-frequency characteristics in the frequency band of 0–600 Hz.

Influence of Inlet Vane and Wrap Angles on Cavitation Behavior of a Centrifugal Pump

This comprehensive study focuses on the relationship between the inlet vane and wrap angles of a centrifugal pump impeller and its cavitation behavior. The objective is to propose a new design for cavitation performance enhancement of the pump by reducing the required net positive suction head (NPSHR). To render a detailed study, the variations of the mentioned angles were examined both at hub and shroud. A three-dimensional two-phase parametric computational fluid dynamics (CFD) study was conducted and variations of inlet blade and wrap angles at hub and shroud were investigated separately. After validating the experimental results with the pump model, the pump parameterization process was carried out, and pump geometry was re-defined with its geometrical properties. The characteristic curves of the parameterized pump and pump model were in agreement with each other. Numerical cavitation tests were performed and the NPSHR values of each design were calculated for four different operating conditions. Results showed that cavitation performance increase was achieved with angle variations at the best efficiency point (BEP) but, this situation led the pump to operate exposed to cavitation at high flows (HF) for some designs. Therefore, the design with the best cavitation performance increased at BEP and HF was proposed as a new design. During numerical simulations, shear stress transport (SST) turbulence model and Rayleigh–Plesset equation were used.