Impeller Outlet Research Articles

Comparison of the Hydraulic Performance and Pressure Pulsation Characteristics of Shaft Tubular Pump Device under Multiple Working Conditions

For pumping station projects in plain areas, shaft tubular pump devices are often used due to the low head. In actual operation, the common working range of the pump device is generally 0.8 Qbep~1.2 Qbep. Therefore, it is of great significance to study the hydraulic performance and pressure pulsation characteristics of the pump device in the working range. In this study, the hydraulic performance of a shaft pump device was tested by a model test, and the internal flow and pressure pulsation characteristics were analyzed by numerical simulation. The results obtained from the model test and numerical simulation were in general agreement, indicating that the numerical results were reliable. The results show that the inlet passage has a good flow pattern in the working range, which may offer a favorable flow state for the impeller. When Q = 0.8 Qbep, the flow in the impeller and guide vane was chaotic, the guide vane had a poor adjustment function on flow direction, and the flow in the outlet passage presented in a spiral motion. When Q = 1.0 and 1.2 Qbep, the flow in the impeller and guide vane was ordered, and the spiral flow in the outlet passage improved. In the working range, the pressure pulsation was similar. The main frequency at the impeller inlet and outlet was consistent with the blade passing frequency. For the same flow rate condition, the amplitude rose from hub to shroud and declined from impeller inlet to outlet. In addition, the amplitude decreased with an increasing flow rate.

Application of CFD to Improve on Reliability and Efficiency of Centrifugal Pump for Oil and Gas Processing Plant

Centrifugal pump is one of the standard pump specification uses in process industries for qualitative and quantitative fluid transfer. Most industrial application of centrifugal pump has mechanical configuration problems that resulted to pump inefficiency and malfunctions. Fault or bad design pumps are characterized due to quality engineering design which prompted this investigation. In this study, CFD code was used to simulate pump efficiency and compared with real experimental studies. Within the limit of simulation experimental error, it was found that, the centrifugal pump was designed within the constraint of pumping at a flow rate of 0.04 m3/s and at a Head of 55-70 m. After the design calculations, the system was model and drawn in SOLIDWOKS, it was found that the pump was given the required material from the software material library in line with the design specifications and parameters using local materials. The performance of the pump was simulated and evaluated to have a flow rate of 0.043 m3/s, velocity of 8.2 m/s with a head of 70 m and various efficiencies ranging from 68.45 - 81.61%. After the analysis was done, 590 it was identified to be the optimum impeller outlet blade angle in which volumetric efficiency and hydraulic efficiency is maximum. The efficiency pressure ratio has also increased; therefore the pump head also increase. Keywords: Flow, pump, efficiency and reliability

Effect of Vibration and Noise Measuring Points Distribution on the Sensitivity of Pump Cavitation Diagnosis

Cavitation is an essential factor in the deterioration of the hydraulic performance of centrifugal pumps. The study of cavitation fault diagnosis can help avoid or reduce the damage it causes. The vibration and noise analysis method can predict the incipient cavitation more accurately. In order to improve the accuracy of cavitation fault diagnosis, this paper studies the distribution of vibration and noise measuring points for centrifugal pump cavitation diagnosis. The research object is a centrifugal pump with an inducer and splitter blades. Vibration acceleration sensors and hydrophones were used to collect structural vibration and liquid-borne noise signals at different positions of the pump unit. Root-mean-square (RMS) and fast Fourier transform (FFT) methods were used to construct spectrums of vibration and noise signals with different NPSH and compare the sensitivity of different measuring points to the inception and development of cavitation. In addition, the SST k-ω turbulence model and Zwart cavitation model were used to study the cavitation volume distribution in the pump under different cavitation stages. By setting monitoring points at the impeller outlet, the frequency domain signal distribution of pressure pulsation was studied. The results show that the vibration acceleration measuring points at the pump inlet flange and pump axial position, and liquid-borne noise measuring point at the inlet position, are more sensitive to the diagnosis of cavitation fault. Motor current is also the basis for judging the inception of cavitation. Moreover, as the cavitation intensifies, the dominant frequency signal of the pressure pulsation in the pump is partially shifted.

Numerical Simulation of Unsteady Cavitation Flow in a Low-Specific-Speed Centrifugal Pump with an Inducer

Cavitation is an undesirable phenomenon in the pumps. In this paper, unsteady cavitation flow in a low-specific-speed centrifugal pump with an inducer is investigated based on the full cavitation model and standard k-ε turbulence model using the commercial software PumpLinx. The numerical results of external performance curve and cavitation performance curve of design condition agree well with that of the experiment. The bubbles in the inducer mainly appear on the outer blade leading edge. The regions of larger vapor volume fraction in the inducer and impeller increase with the decreasing of NPSHa. The regions of larger vapor volume fraction in the inducer expand from the outer edge of the blade inlet to the hub on suction surface. Under very low NPSHa, the impeller may be filled with bubbles in the passage and the pump head drops drastically, and there exist distinct back flows near the suction surface of the blade and impeller outlet. Affected by pre-swirl of inducer outlet and the circle flow of impeller blade inlet, the amplitude of pressure fluctuation near the impeller inlet is obviously larger than that at the inlet in the inducer. The dominant frequency of pressure fluctuation for four monitoring points is shaft frequency. Compared with the non-cavitation flows, the maximum amplitudes of pressure pulsation increase for cavitating flow.

Optimization design for an impeller of the multiphase rotodynamic pump handling gas-liquid two-phase flow

The multiphase rotodynamic pump is crucial for the multiphase blending transportation process. However, desigining such pump with high hydraulic performance and good blending transportation ability is quite challenging because of its unique structure. This study constructed a multi-objective optimization design system, which combines the 3D inverse design theory, response surface methodology, genetic algorithm, computational fluid dynamics simulation, and multi-objective optimization strategy, to improve the multiphase pump performance. Five optimization variables, namely the impeller loading parameters ( m1,S, m1,H, kS, kH) and the high-pressure edge angle ( θ), were selected in this study. Furthermore, two optimization objectives were considered at inlet gas void fraction ( IGVF) = 10%, namely the pump efficiency and the gas uniformity at the impeller outlet. The optimization results demonstrated that the pump efficiency and blending transportation ability would improve if the impeller blades had for-loaded loading distribution and the negative high-pressure edge angle. After optimization, the pump efficiency and the gas uniformity for the optimized impeller Opt1 improved by 2.6% and 18.2% at IGVF = 10%, respectively. Moreover, the internal flow pattern in the impeller was improved significantly, resulting in the maximum amplitude of pressure fluctuation in impeller Opt1 being 0.42 times that in the original test impeller.

Experimental and Numerical Investigation of Stall Mechanism in Centrifugal Pump Impeller

Stall is a complex flow phenomenon in centrifugal pumps at part load conditions. However, there is no clear description of the stall evolution process and mechanism, which is critical for stall control. Based on a high-frequency Particle Image Velocimetry (PIV) system (10k Hz) and a non-refraction experimental bench, emphasis is laid on the flow structures near the initial stall conditions. The results show that as the flow rate decreased, the flow separation occurred at the middle of the blade suction side and then evolved into a stall vortex which moved to the impeller’s inlet direction and kept growing. Subsequently, it broken into two vortexes when reaching the location where the impeller cross-sectional area is the smallest. One stall vortex continued its motion toward the passage inlet direction, while the other vortex separates to the impeller outlet. As the stall vortex’s size at the impeller inlet enlarged, the flow incident direction at the impeller inlet was directed to the blade suction side, which caused the stall vortex on the suction side to disappear. The stall mechanism is explained in detail using both experiments and numerical simulations. Meanwhile, the Scale Adaptive Simulation-Shear Stress Transport (SAS-SST) hybrid model is used to simulate several flow rate conditions near the stall initial stage. The findings indicate that the increasing adverse pressure gradient and the high-pressure zone move along the suction blade towards the impeller inlet as the flow rate is reduced; however, the relative velocity is constantly decreasing. When the fluid can’t provide enough kinetic energy to maintain its continuous flow along the suction surface, flow separation occurs. The stall vortex, which results from flow separation, blocks the passage impeller. The increasing adverse pressure from the impeller outlet to the inlet is the main cause of flow separation; and the adverse pressure gradient is a major manifestation of the stall vortex.

Matching performance of single channel pump by the combination of various cross-sectional shapes of impeller outlet and volute casing

Matching performance of single channel pump by the combination of various cross-sectional shapes of impeller outlet and volute casing

Sensitivity analysis on the influence factors of clearance axial force of a varying-speed centrifugal pump

Abstract Hydraulic axial force is an important parameter of the performance of centrifugal pump. It strongly affects the operation stability and the life-time of thrust bearing. Under the influence of flow pressure distribution, the hydraulic axial force of centrifugal pump has mainly two parts. One is the force inside impeller while the other is the force in clearance. In this case, the situation is more complex because the pump operates with varying-speed. Under the influence of rotation speed, pump head and minimum clearance width, the variation law of clearance axial force is still not fully understood. Therefore, the orthogonal experiment is conducted based on Large Eddy Simulation (LES). The local flow and hydraulic axial force in impeller shroud clearance is mainly studied. Results show that the pressure difference between impeller inlet and outlet will strongly impact the pressure distribution in clearance. Then, it affects the clearance axial force. The rotation speed and pump head are proved influential. However, range analysis shows that the minimum clearance width is the most dominant factor. It can somehow adjust the pressure distribution in clearance. The geometric design of impeller clearance will be important in reducing hydraulic axial force especially for varying-speed centrifugal pumps.

Investigation of the hydrodynamic characteristics of an axial flow pump system under special utilization conditions

In actual operation, axial flow pump stations are often used for various special purposes to meet changing needs. However, because the hydrodynamic characteristics of axial flow pump systems are still unclear when used for special purposes, there are many risks when pump systems are used for special purposes. To explore the hydrodynamic characteristics of an axial flow pump system under special utilization conditions, a high-precision full-feature test bench for an axial flow pump system is established in this paper. For the first time, an energy characteristics experiment and a pressure fluctuation measurement for a pump are carried out for a large axial flow pump system model under zero head, reverse pump and reverse power generation conditions. Then, ANSYS CFX software is used to solve the continuous equation and Reynolds average Navier–Stokes equation, combined with the SST k–ω turbulence model, and the characteristic curve and internal flow field of the pump system under special conditions are obtained. Finally, the numerical simulation results are compared with the experimental results. The results show that the velocity gradient distribution in the pump is uniform under the near zero head condition (NZHC), and there is no obvious flow collision and reflux phenomenon in the pump. Compared with the designed condition (DC), the peak-to-peak value (PPV) of pressure pulsation at the inlet of the impeller decreased by 67.16%, and the PPV at the outlet of the impeller decreased by 8.14% at H = 0 m. The maximum value of the main frequency amplitude (MFA) in the impeller area appears at the impeller inlet. Under reverse pump conditions (RPC), the phenomenon of unstable flow in the pump system is obvious, and a large range of recirculation zones appears in the nonworking face of the blade. Compared with the DC, the PPV of the impeller inlet at the optimal point of RPC increased by 122.61%, and the impeller outlet PPV increased by 11.37%. The maximum value of MFA in the impeller area appears at the impeller inlet. Under the reverse power generation condition (RPGC), no obvious flow separation was found in the nonworking face of the impeller. Compared to the DC, the PPV of the impeller inlet at the optimal point of the RPGC increased by 65.34%, and the PPV of the impeller outlet increased by 206.40%.

Research on the energy characteristics of reactor coolant pump under flow coastdown transient

In order to research the energy characteristics in impeller, guide vane and volute of reactor coolant pump under flow coastdown transient. In four typical states the variation laws of dynamic–static pressure energy and entropy generation in hydraulic components were analyzed under flow coastdown transient. The results show that after the occurrence of flow coastdown transient, the decreasing rate of energy conversion efficiency of impeller is similar that of the rotating speed. With the development of flow coastdown process, the high dynamic pressure energy distribution of impeller deviates to the outlet of impeller. After 0.25TQi, the energy retained by impeller is basically consumed. In guide vane passage, the change of dynamic pressure energy first increases and then decreases, and the static pressure energy firstly decreases and then increases. After 0.75TQi, the diffusivity of the guide vanes to the fluid decreases rapidly. With the development of flow coastdown process, the main working area of guide vane gradually shifts from the middle of guide vane to outlet. High static pressure energy area at guide vane inlet is enlarged and then reduced. With the development of flow coastdown process, the dynamic pressure energy of V2 and V4 at the monitoring points of volute changes alternately, and the dynamic pressure energy of right tongue region of volute gradually exceeds 11.20 m, and the energy conversion effect of volute gradually weakens, and the low static pressure energy region of the right tongue gradually disappears. Compared with other conditions, at 1.0TQi, the loss of dynamic pressure energy in volute is faster, while the reduction rate of static pressure energy is more stable. Entropy generation in reactor coolant pump varies in a similar manner to flow rate and speed, and is closely related to dynamic-static pressure energy. Both Total Entropy Generation (TEG) and per unit volume of entropy generation (Sˈ) eventually approach zero. Entropy generation ratio of volute is much larger than that of other areas, accounting for more than 60%. Guide vane area generates more per unit volume of energy loss than other areas. The flow in impeller under 0.5TQi condition is more stable than that under other conditions. The unstable flow in reactor coolant pump at the initial stage of flow coastdown transient is more severe and has a greater energy loss than under other conditions. After flow coastdown, great damage may occur in the impeller blade inlet area, the guide blade inlet area, the left area of the volute and the volute tongue area.

Research on Multi-Optimal Project of Outlet Guide Vanes of Nuclear Grade Axial Flow Fan Based on Sensitivity Analysis

Nuclear grade axial flow fans are widely used in nuclear power plants for ventilation and heat dissipation and have the advantages of high efficiency and high flow rates. A nuclear grade axial flow fan with OGVs (outlet guide vanes) can recover the kinetic energy of the dynamic impeller outlet winding to increase the ventilator pressure, thus improving the ventilator efficiency; therefore, the OGVs play an essential role in the performance of the axial flow fan. Based on accurate numerical simulations, an MRGP approximation model was developed to analyse the factors affecting the OGVs duct and optimise the guide vane structure, combined with the Sobol method for sensitivity analysis. The experiments and numerical simulations show that the total pressure of the optimised model increases by 154 Pa, and the noise decreases by 4.1 dB. The multi-objective optimisation method using the parametric approach and combining it with the MRGP model is highly reliable. It provides a key design direction for optimising nuclear grade axial flow fans.

Investigation of the Effect of the Stages Number, the Impeller Outlet Width, and the Impeller Outlet Angle on the Performance of an Industrial Electric Submersible Pump

Abstract This study has investigated the effect of the number of stages, the blade outlet spacing, and the blade outlet angle of a selected industrial submersible pump on the pump performance. The main steps in the study are outlined below: Firstly, the operating characteristics in different stages of a selected industrial submersible pump were measured by the experiment. Following the measurements, the effects of two basic geometric parameters, such as impeller outlet width and impeller outlet angle on the pump performance were examined with computational fluid dynamics (CFD) simulations verified by the experimental measurements. It was seen that the geometric parameters, which were considered in the simulations, changed the size of the time-dependent variables, but the flow structure did not. Another striking finding from the CFD simulations carried out is it has been observed that while geometric arrangements have a partial effect on the flow structure along with the pump, they cause a difference in the critical values on the basic variables that define pump performance, such as pressure.

Investigation on Broadening Compressor Surge Margin by Using Active Magnetic Bearing

The impeller design usually expects to achieve high efficiency and a wide working range while they are influenced by tip clearance in different ways. In this study, a blower with a controllable magnetic suspension bearing was studied. The magnetic bearing enables the impeller to adjust the tip clearance during operation to optimize the efficiency of the blower at the design point and significantly expand the surge margin when it deviates from the design point. The clearance ratio (CR) is defined as the ratio of tip clearance over impeller outlet width. The computational fluid dynamics (CFD) method is used to study the performance of a centrifugal impeller under CR = 2.61%∼7.83% and verified by experiments. The results show that the pressure ratio and efficiency of the impeller at the design point decreased linearly with the increase of the gap. For each 1% increment in CR, the pressure ratio reduces by 0.02 and the polytropic compression efficiency declines by 0.5%. Conversely, the surge margin increases with the expansion of CR. For every 1% rise in CR, the surge margin would improve by 7.8%. A control method of changing the reference suspension position according to the optimal efficiency fitting model is proposed. It realizes the real-time control of the axial suspension position of the impeller according to the changes of pressure and flow rate signals to obtain the optimal work efficiency with a broad surge margin. Experimental results show that using an impeller equipped with a controllable magnetic suspension bearing could minimize the gap stably in the nonsurge area to obtain high efficiency, and when necessary, it could enlarge the gap to meet the low flow rate condition.

Influence of Blade Angle Deviation on the Hydraulic Performance and Structural Characteristics of S-Type Front Shaft Extension Tubular Pump Device

When the axial-flow pump is running, the blade angle is not fully adjusted or there are errors in the manufacture of the blades, which will lead to inconsistent blade placement angles during operation, and which will reduce the efficiency of the axial-flow pump. This paper uses the research methods of numerical simulation and model experiments to analyze the hydraulic performance and impeller structure characteristics of each flow components under different schemes when the angles of each blade of the S-type front shaft extension tubular pump device are inconsistent. The research phenomenon is that the guide vane greatly recovers the flow velocity circulation at the impeller outlet, reduces the hydraulic loss of guide vane, and widens the best efficiency range with an increase in guide vane blade angle. When the blade angle deviation occurs, the flow field of each blade channel affects each other, and the maximum decrease in the best efficiency is up to 7.78%, mainly due to the increased hydraulic loss in the outlet channel. The blade angle deviation will also affect the maximum equivalent stress and maximum deformation of the impeller, which is more obvious in large flow conditions. Inconsistent blade angles seriously affect the operating efficiency of the water pump and water pump device, and make the structural characteristics of the impeller worse.

Effect of impeller shroud trimming on the hydraulic performance of centrifugal pumps with low and medium specific speeds

The effect of pump impeller modification by a new approach, pump impeller shroud trimming (PIST), on the flow field and pump performance is examined both numerically and experimentally. The primary purpose of this study is to investigate the hydraulic performance of single-phase centrifugal pumps, which are refined by the PIST method, with low and medium specific speeds. In this type of shroud trimming, different trimming sizes are applied only to the shroud plate of the closed impeller, while the geometries (diameters) of the hub and blades remain unchanged. This modification, which increases the clearance between the impeller and casing from the shroud side, causes desirable conditions for pumping fluid containing undissolved gas. Computational fluid dynamics software (ANSYS-CFX) is used to predict the hydraulic performance of centrifugal pumps. Two well-known turbulence models, the renormalization group (RNG) k-ϵ developed model and shear stress transport (SST) k-ω, are used to predict the flow patterns. The computational results are verified through the comparison of experimental and unsteady numerical simulations with steady numerical data. After ensuring the accuracy of the flow-field simulation approach, further numerical analysis is performed for both pumps by changing the impeller shroud diameter. The effects of the geometric changes on the performance curves, efficiency, flow field, pressure distribution inside the pump components and the radial force acting on both pump types are investigated comprehensively. The results show that the shroud trimming reduces the produced head and efficiency at the design points. Examination of the radial force, which is applied on the rotating parts, shows that shroud-trimmed impellers experience higher radial forces than closed impellers in both pump types owing to the lack of a uniform pressure distribution around the impeller outlet. Accordingly, the relevant information obtained is used to modify the existing coefficients to predict the radial forces.

An Analysis on Hydraulic Loss in a Co-Rotating Bladed Disc Pump

Disc pumps rely on the shear force generated by a co-rotating disc to transport the fluid, the interaction between the fluid and impeller is weak, providing such pumps advantages when handling multi-phase flow. In the present study, a loss analysis is presented on a different kind of disc pump that combines both shear and pressure forces using a co-rotating disc pump and radial blades and that is often applied in marine petroleum engineering for mud-lifting. Experimental measurements on the overall pump performance were performed, and the subsequent hydraulic efficiency analysis shows that similarity laws can be applied for this pump. A particular analysis was specifically performed on the impeller and shows that the resulting loss analysis indicates that the increase in the static pressure is small and that the total pressure increase is mainly contributed to by the dynamic pressure change from the inlet to the outlet impeller sections. In addition, an evaluation of the individual loss levels is proposed in the impeller that is based on one-dimensional assumptions. This type of evaluation has never been proposed for present specific TBD pump designs in the available literature. The obtained results showed that the most important loss levels are roughly equally distributed between the incidence effects, inter-blade leakage, and bolts losses in the impeller, and that all together, they can reach 80% of the total impeller losses, while the blade-loading and friction losses are relatively small. The losses downstream of the impeller are significant; thus, a specific volute design that has been adapted for a disc impeller outlet flow pattern must be considered in order to achieve better performance. The present loss analysis was able to predict the corresponding disc pump performance well, achieving a maximum error rate of ±5% for a rather wide flow coefficient range. The proposed method can be considered to be a useful approach for research or for industrial teams who are working on the same kind of geometry by adopting the same data reduction analysis, allowing them to compare their own results with the present ones.

The external characteristics and inner flow research of rim-driven thruster

In order to have a more comprehensive grasp of the performance of the rim-driven thruster, the external characteristics are studied by experiment and carry out numerical simulation to study inner flow characteristics. The test results for the rim-driven thruster find that the head curve had a hump shape. The head is the largest while the flow rate Q = 600 m3/h. The numerical simulation is carried out to reveal the cause of the hump of head. The results show that large-scale backflows gradually appear near the wall in front of the impeller inlet, the central area of the impeller outlet, and the two sides of the central low-pressure zone with the reducing of the flow rate, which can cause a large flow loss and result in a drop in head. The discrepancy between the pressure surface and the suction surface of blade decreases rapidly in the range of r/ R = 0.2–0.5, which is another major factor leading to the drop in head under small-flow conditions. Structurally, there is no blade in the impeller center and there are the large backflows in the middle of impeller, which causes much volume loss and is a main cause of the decreasing of head under small flow rate.

Research on the Matching Characteristics of the Impellers and Guide Vanes of Seawater Desalination Pumps with High Capacity and Pressure

This paper presents the matching characteristics of impellers and guide vanes of high capacity and pressure seawater desalination pumps by using computational fluid dynamics (CFD). The single-stage pump is numerically calculated, and its external characteristics are consistent with the test results of model pump. Taking this scheme as a prototype, the research is carried out from three aspects: (i) the impeller blade outlet width; (ii) the number of impeller and guide vane blades; and (iii) the area ratio of impeller outlet to guide vane inlet. The results indicate that the blade outlet width significantly affects the pump head and efficiency. Appropriately increasing the number of guide vane blades or changing the number of impeller blades can improve efficiency and expand the high-efficiency area. Additionally, increasing the throat area of the guide vane has the opposite effect on the large flow and small flow area of the pump. An optimized hydraulic model design scheme is obtained.

Investigation of Unsteady Pressure Pulsation in New Type Dishwasher Pump with Special Double Tongue Volute

Through numerical simulations, this work analyzes the unsteady pressure pulsation characteristics in new type of dishwasher pump with double tongue volute and single tongue volute, under volute static and rotation conditions. Likewise, the performance tests were also carried out to verify the numerical results. Multiple monitoring points were set at the various positions of new type dishwasher pump to collect the pressure pulsation signals, and the relevant frequency signals were obtained via Fast Fourier Transform, to analyze the influence of volute tongue and its passive speed on the pump performance. The results reveal that when the double tongue volute is stationary, the pressure pulsation amplitudes increase from the impeller inlet to the impeller outlet. Under the influence of shedding vortex, the pressure pulsation in the lateral region of tongue becomes disorganized, and the main frequency of pressure pulsation changes from blade frequency to shaft frequency. In addition, compared with the static volute, double tongue volute can effectively guide the water flow out of the tongue during the rotation process, thus ensuring good periodicity for pressure pulsation in the tongue region. Accordingly, a volute reference scheme with passive rotation speed is proposed in this study, which can effectively improve the pressure pulsation at tongue position, and provides a new idea for rotor-stator interference to guide the innovation of dishwasher.

Laboratory Modeling of an Axial Flow Micro Hydraulic Turbine

This article is devoted to detailed experimental studies of the flow behind the impeller of an air model of a propeller-type microhydroturbine in a wide range of operating parameters. The measurements of two component distributions of averaged velocities and pulsations for conditions from part load to strong overload are conducted. It is shown that the flow at the impeller outlet becomes swirled when the hydraulic turbine operating mode shifts from the optimum one. The character of the behavior of the integral swirl number, which determines the state of the swirled flow, is revealed. Information about the flow peculiarities can be used when adjusting the hydraulic unit mode to optimal conditions and developing recommendations to expand the hydraulic turbine operation control range with preservation of high efficiency. This stage will significantly save time at the stage of equipment design for specific field conditions of water resource.