Showing papers on "Impeller published in 2023"

Energy performance evaluation of an axial-flow pump as turbine under conventional and reverse operating modes based on an energy loss intensity model

Abstract: As a low-cost scheme for small-scale hydropower generation, pump as turbines (PATs) are used at different hydrosites around the world. Nevertheless, a big number of recently conducted studies on PAT performance have mainly focused on the centrifugal type, despite the fact that the axial-flow type has a comparatively large flow capacity, thus disposing of higher power density. Therefore, this article seeks to investigate the flow dynamics of an axial-flow PAT and associated energy loss characteristics, under both pump and turbine operating modes. It adopts the numerical simulation method and uses entropy production theory to propose an energy loss intensity model in the cylindrical coordinate system, which quantitatively gives the spatial variation pattern for energy losses in pump and turbine operating modes. In addition, the correlation between energy loss and flow instability is deeply analyzed, where the energy characteristics in pump and turbine modes are quantitatively evaluated. It is shown that the energy loss within the impeller and the guide vane flow fields, for both operating modes, is mainly because of the turbulent entropy production. The proportion of direct entropy production and wall entropy production is found to be relatively small. The velocity gradient, flow vorticity, turbulence intensity, and energy losses within the flow passages of the axial-flow PAT have been closely related. However, owing to the difference in PAT operating modes, there is a significant difference in the location of energy losses. The unstable flow phenomena, such as the impact at the blade inlet, flow deviation at the blade outlet, flow separation, back-flow, and vortex, are the main reasons for entropy production. This study serves as a reference for the design, optimization, and application of axial-flow PATs.

Assessment of cavitation noise in a centrifugal pump using acoustic finite element method and spherical cavity radiation theory

Abstract: To examine the cavitation noise characteristics of centrifugal pumps, the combination of test and simulation was applied in this study. The numerical method is based on spherical cavity radiation theory and the acoustic finite element method. A multi-field synchronized test-rig was built to study and validate the numerical results under cavitating flow and cavitation noise conditions. The three-dimensional unsteady flow-field simulation was carried out inside the centrifugal pump based on DES and the improved-RZGB cavitation model. The constructed numerical method for cavitation noise was used to solve the acoustic-field based on the flow-field solutions. The test–simulation comparison reveal that the numerical simulation results are consistent and reliable. The development of cavitation has a stronger influence on the strong vorticity regions in the impeller flow channel, and the vortex has a promotional-effect on the formation of cavitation. With the same cavitation number, the acoustic-power on the blade suction-side is greater than the pressure-side of the blade. As the cavitation number decreases, the pulsating radiated noise of cavitation volume is the primary noise-source for the increased acoustic-power value. At this stage, the SPL and total SPL at the model pump inlet show a decreasing trend during the severe cavitation-stage.

Investigation of energy loss mechanism of shroud region in A mixed-flow pump under stall conditions

Abstract: The energy consumption of various pumps accounts for almost 20% of the world’s electricity production, and the improvement of pump efficiency could save enormous energy consumption globally. In a mixed-flow pump, the hydraulic loss within the shroud region accounts for almost 30% of the whole loss in the impeller, which is an inevitable factor. Therefore, in this study, the loss near the end wall of impeller caused by the tip leakage flow (TLF), secondary flow and disorder flow, etc., is quantitatively investigated by the entropy production loss theory. The purpose is to find out the serious region of energy loss and conduct the structure optimization in the future. The research shows that the tip leakage vortex (TLV) and the TLF “jet effect” are responsible for the hydraulic loss within the shroud region in the designed flow fields. In the stall flow fields, some unsteady flow components are the additional loss source, such as the secondary flow vortex, separation flow vortex, secondary TLV, and wake vortex. In the deep stall flow fields, the coupling effect between reverse flow near shroud and inlet swirling flow would be the source of periodicity stall characteristic with high possibility.

Theoretical models and dependences for calculating intensity of hydroabrasive wear of pump working parts

Abstract: The paper presents the results of a theoretical and experimental study of the wear intensity of the elements of the flow part of centrifugal and axial pumps. Theoretical formulas recommended by various authors, obtained for models with flat samples based on energy theory, do not consider the features of hydraulic machines. Considering the movement of a solid particle in the interblade channels of the impellers of centrifugal and axial pumps, we chose design schemes that correspond to hydraulic and physical wear processes. The analysis shows that the action of centrifugal and inertial forces in the interblade channel of the impellers of centrifugal and axial pumps results in the separation and redistribution of solid particles in the flow. As a result, in centrifugal pumps at the end of the blade and axial pumps at the end gap of the impeller, the local concentration of solid particles increases compared to the average. The paper also provides dependencies for calculating the intensity of hydroabrasive wear of pump working parts.

Internal Flow Characteristics of High-Specific-Speed Centrifugal Pumps with Different Number of Impeller Blades under Large Flow Conditions

Abstract: As compared with a conventional centrifugal pump, a high-specific-speed centrifugal pump mostly operates under large flow conditions. In this paper, a typical high-specific-speed centrifugal pump is examined, and the effect of the blade number on the internal flow condition is investigated numerically. The numerical predictions have been verified through measurement. It was found that the predictions and the measurements are in good agreement of discrepancy. Serious cavitation could be observed within the pump when the flow rate reached 1300 m3/h. Meanwhile, the effect of the blade number on the cavitation intensity was extremely obvious. The cavitation area at the inlet edge of the blades significantly reduced when the blade number increased from three to six. In addition, the turbulent kinetic energy within the pump was more uniformly distributed. This demonstrates that the blade number can be reasonably chosen to improve the internal flow pattern within the pump, which could provide a theoretical basis for the practical application of high-specific-speed centrifugal pumps.

Research on energy conversion characteristics in impeller of Helico-Axial Multiphase Pump during crude transportation

Abstract: In order to explore the influence of different crude viscosity on the energy conversion characteristics of impeller of Helical-Axial Multiphase Pump, it was carried out numerical simulation which based on the standard k-ε equation and Euler multiphase flow model under different viscosity. At the same time, Helical-Axial Multiphase Pump was analyzed internal flow structure of by experiments when transported water. The changes of pressure, GVF（gas volume fraction）, flow field and pressurization are obtained in impeller with different viscosity and IGVF（inlet gas volume fraction）.The results show that liquid viscosity is greater, the inlet pressure of impeller increasing, velocity vector is greater near rim and hub side, increasing of turbulent kinetic energy of the hub side and rim side, resulting in greater flow loss. The pressurization capacity of impeller is weakened, making its head is lower. At the same time, the fluctuation of GVF from inlet to outlet is smaller, and the low GVF area is mainly concentrated in high pressure area. The viscosity has a greater impact on static pressure energy of the first half of impeller, and a smaller impact on the second half of impeller, and the power of impeller is mainly concentrated in the first half of impeller.

CFD Simulation of Centrifugal Pump with Different Impeller Blade Trailing Edges

Abstract: The centrifugal pump is one of the most widely used types of power machinery in the field of ship and ocean engineering, and the shape of the impeller blade trailing edge has an important influence on their performance. To reveal the mechanism of the effect of different trailing edges on external performance, the internal flow of 16 types of impeller blade trailing edges of a centrifugal pump, consisting of Bezier trailing edges, rounding on the pressure side, cutting on the suction side, and the original trailing edge is studied by numerical simulation. The reverse flow, shaft power, and energy loss distribution in the impeller and diffuser along the streamwise direction are analyzed by calculating them on each micro control body sliced from the fluid domain. The entropy production theory and Ω-vortex identification method are used to display the magnitude and location of energy loss and the vortex structure. Finally, a static structural analysis of the impeller with different trailing edges is performed. The results show that different impeller trailing edges can clearly affect the efficiency of the pump, i.e., the thinner the trailing edge, the higher the efficiency, with the thickest model reducing efficiency by 5.71% and the thinnest model increasing efficiency by 0.59% compared to the original one. Changing the shape of the impeller trailing edge has a great influence on the reverse flow, shaft power, and energy loss near the impeller trailing edge and diffuser inlet but has little influence on the leading part of the impeller. The distribution of local entropy production rate, energy loss, and reverse flow along the streamwise direction shows similar rules, with a local maximum near the leading edge of the impeller due to the impact effect, and a global maximum near the impeller trailing edge resulting from strong flow separation and high vortex strength due to the jet-wake flow. Thinning the impeller trailing edge and smoothing its connection with the blade can reduce the vortex strength and entropy production near the impeller trailing edge and diffuser inlet, improve the flow pattern, and reduce energy loss, thus improving the pump efficiency. In all models, the maximum equivalent stress is less than 6.5 MPa and the maximum total deformation is less than 0.065mm. The results are helpful for a deeper understanding of the complex flow mechanism of the centrifugal pump with different blade trailing edges.

Study on the blade squealer tip affecting tip leakage flow and performance of a multiphase pump

Abstract: To improve the adverse effects of tip leakage flow on the multiphase pump, a method to design a squealer tip on the impeller blade was proposed in this paper. The effect of the squealer tip on external characteristic, tip clearance flow characteristic and energy dissipation of the multiphase pump are analyzed. Research results indicate that the blade squealer tip can effectively improve hydraulic efficiency of the multiphase pump. At the optimal efficiency point, the head and hydraulic efficiency of the multiphase pump with squealer tip increased by 3.62% and 4.15% respectively compared with the original model. The influence of tip leakage flow in the axial rear half passage of the multiphase pump impeller is far greater than that in the axial forward half passage, especially on the back position in the middle of the impeller passage. The squealer tip can restrain the reverse of leakage flow from the pressure side to the suction side of the impeller blade and the clearance leakage flow of the model with squealer tip is smaller than that of the original model. The squealer tip on blade will reduce the energy dissipation caused by unsteady flow in the mainstream. The research results in this paper can provide theoretical support for effectively restraining the influence of the tip leakage vortex on the mainstream of the helicon-axial multiphase pump, and contribute to engineering practice value of improving the performance of the multiphase pump.

Gas-liquid Transport Behaviors and Mass Transfer Mechanism During Oxygen Dissolution and Evolution Processes in a Micropump

Abstract: On-orbit refueling and space circulation technologies involve the use of a space micropump to transport gas-liquid mixed fluids, which affects the gas-liquid mass transfer and dynamic behaviors. To predict dynamic mass transfer processes, our proposed dissolved and released models were applied to space micropump calculation after the verification of dissolved oxygen concentration and micropump energy characteristics. The mass transfer characteristics and gas-liquid states were investigated by combining the correlation analyses. The results show that the dissolved concentration and the volume fraction are considered to be strongly related to the mass transfer rate, and the effect of turbulence kinetic energy cannot be ignored particularly in impeller and volute. Based on this, the gas-liquid state parameters are focused on unidirectional dissolved and bidirectional released-dissolved conditions. The released gas occupied the head of the suction surface of the long blades and developed downstream, and its presence causes a significant gas increase in downstream. According to the mass-transfer characteristics comparisons, the oxygen increment deceases as the inlet dissolved oxygen concentration increases, exhibiting the similarity of two-film theory. In addition, the evolution increases the fluctuation in the gas volume fraction and the total hydraulic loss. The current study provides guidance for the fueling gas-liquid mixed delivery status, and the dissolved gas concentration must be controlled strictly to avoid the evolution of gas to ensure the safety and decrease the flow loss.

Research on Pressure Fluctuation Induced by Tip Leakage Vortex of Axial Flow Circulating Pump under Unpowered Driven Conditions

Abstract: Axial flow circulating pumps (AFCP) are one of large marine steam turbine unit for large-sized ships. One peculiar operation condition for AFCP is when a ship cruises beyond a certain speed, the energy of pump inflow is able to completely overcome the frictional resisting moment of the pump itself, thereby driving the impeller to rotate. Such a condition is also known as the unpowered driven condition (UDC). At this time, the fluid is in the artesian flow state. In this paper, pressure fluctuation and inner flow of the AFCP under UDCs and different inflow conditions are analyzed using DDES turbulence model. It is found that the intensity of TLV decreases from the leading edge to the trailing edge of the blade, and the amplitude of pressure pulsation caused by TLV also decreases. Due to the jet wake structure at the blade trailing edge, the amplitude of pressure fluctuation at the trailing edge of the blade increases by 7.8% under the optimal UDC. In addition, the compression-expansion term determines the strength of TLV's core, thus affecting the amplitude of pressure fluctuation. The viscous dissipation effect of TLV can cause high frequency components of pressure fluctuation.

Flow Capacity Optimization of a Squirrel Cage Fan with a New Rounded Rectangle Volute under Size Limitation

Abstract: Squirrel cage fans (SCFs) are widely used in a variety of household appliances. Due to the restriction on installation size, the design of high-efficiency SCFs with high flow capacities is an important topic. In this study, we proposed a novel rounded rectangle volute profile (RRVP) for the design of compact high-flow SCFs. At first, we used computational fluid dynamics (CFD) to simulate the aerodynamic performances of three SCFs having the same impeller but different volutes, which were the common logarithmic-spiral volute profile, the cutting volute profile, and the RRVP volute at the maximum flow rate working condition. The CFD simulations indicate that the fan with RRVP volute has the highest flow rate at the maximum flow rate working condition. Then, we proposed a parameterization method for the RRVP with 16 control variables. The multiobjective evolutionary algorithm based on decomposition (MOEA/D) and Kriging model was used to optimize the aerodynamic shape of the compact SCF with an RRVP volute. Twenty-three control variables were used in the multiobjective optimization process, including the optimization of the blade angles and the impeller position. Optimization results show that the maximum volumetric flow rate of the optimal SCF with an RRVP volute increases from 147.1 cubic feet per minute (CFM) to 191.1 CFM, and the fan efficiency also increases from 32.21% to 33.5%, compared with the original SCF with the common logarithmic-spiral volute. Two main factors were found to increase the flow capacity and efficiency of the optimal SCF under strict size constrains. First, the RRVP became smooth and large, which reduced the flow loss and increased the flow cross-section; second, the eccentrically mounted impeller of the optimal fan enlarged the flow section near the outlet of the volute.

Transient Hydrodynamic Behavior of a Pump as Turbine with Varying Rotating Speed

Abstract: The working condition of a centrifugal pump as a turbine (PAT) is often unsteady. The rotating speed of a PAT constantly varies as the flow and load change, resulting in transient hydrodynamic behaviors between different working conditions. During the transition, the PAT undergoes a severe change in performance and complicated internal flow structures. In previous work, the fixed rotating speed of a PAT was mostly considered using computational fluid dynamics. To investigate the transient behavior of a PAT, relevant simulation tools are developed to depict transient flow conditions, and the corresponding transient speed of the impeller is calculated. Both large and small fluctuation transitions are simulated for the practical application of the PAT. The simulated results are first verified by experiments. The results show that the rotating speed significantly affects the performance and stability of the PAT. The rapid increment in flow rate and rotating speed lead to large energy dissipation in the internal flow field of the PAT. The range of high efficiency of the PAT expands and migrates to the high flow rate range. The efficiency in the transition condition started a cyclic growth after the flow reached 60 m3/h, and it reached a peak at around 80 m3/h, which was about 5% lower than the calculated value in a quasi-steady state. In the range of high rotating speeds, the rotating speed of the impeller and the operational stability are sensitive to flow fluctuation. The internal flow fields during transition conditions are analyzed as well. The obtained results can be utilized as a reference for studying the hydrodynamic characteristics and stability of fluid machinery in the transition under transient flow conditions.

Numerical Simulation on the Influence of Inlet Flow Characteristics on the Performance of a Centrifugal Compressor

Abstract: Although inlet bent pipes are usually adopted due to limited installation space, the influences of different bend pipes on the inlet flow characteristics and performance of centrifugal compressors are still unclear. The numerical simulation of a centrifugal compressor is established and validated by experimental results with the case of a straight inlet pipe. Then, the internal flow characteristics of the centrifugal compressor with a 90-degree bent pipe (p90) and Z-shaped bent pipe (pz) are simulated and discussed. The results show that the adoption of two inlet bent pipes reduces the performance of the centrifugal compressor to a certain extent, which reduces more greatly with pz, with a maximum reduction of 6.82% in pressure ratio and 14.83% in efficiency, respectively. The pressure ratio and efficiency reduction of the centrifugal compressor both increase with the increment of distortion degree, which maintains the increasing trend as the flow rate increases, and the maximum distortion degree of p90 and pz reaches 0.0351 and 0.0479, respectively. The reduction degree of the pressure ratio shows a power–law relationship with the distortion degree, while the reduction degree of efficiency shows an exponential relationship with it. The flow characteristics at the outlet section of the inlet pipe affect the flow field distribution at the inlet of the impeller, and the distortion area ranges of the total pressure and axial velocity at the inlet of the impeller are near 72°–144° in the circumferential direction for p90, while those of pz are close to 108°–180° and 288°–360°. When the flow with a high distortion degree enters the impeller, a large area with high turbulent kinetic energy is formed in the downstream flow channel, resulting in an increase in the flow loss.

A Review of Turbine and Compressor Aerodynamic Forces in Turbomachinery

Abstract: Aerodynamic forces due to blade-tip clearance eccentricity are a known destabilizing source in rotating machinery with unshrouded impellers. Dynamic forces also appear in shrouded impellers, due to changes in the pressure in the gap between the impeller casing and its shroud. These are load-dependent forces typically characterized by a cross-coupled stiffness coefficient (k > 0). This paper reviews the archival literature for quantification of blade-tip clearance induced forces and impeller-casing forces in both unshrouded and shrouded turbines and compressors. Most distinctive are the lack of experimental results and the indiscriminate application of simple formulas to predict k, including Alford’s and Wachel’s equations. The disparity in estimations of the destabilizing k extends to recent CFD models and results. Hence, rotordynamic predictions vary widely. This review reveals that engineering practice ignores accurate physical models that could bridge the gap between practice and theory. As the energy market shifts toward carbon capture and hydrogen compression, accurate knowledge of aerodynamic forces from unshrouded compressors and open impellers will become necessary in multi-stage rotors.

Experimental and Numerical Study on Cavitation Effects in Centrifugal Pumps

Abstract: 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.

Influence of hydroabrasive wear of impeller blades on head of centrifugal pump

Abstract: The results of experiments on studying the nature of changes in the concentration and dispersion of solid suspended particles showed that the highest average monthly sediment concentration is 2.5...3.8 kg/m3, and sometimes in rainy weather, the maximum water turbidity reaches 7kg/m3. In the composition of solid mechanical impurities, a significant amount consists of particles with a grain size of 0.1-0.05mm. Observations have established that particles larger than 0.01 mm at a low flow velocity in the supply channel and the water intake chamber of the pumping station were easily deposited in them. Siltation volumes at various stations ranged from 20 to 60%. As a result, the hydraulic resistance increased, which led to a decrease in the pump head. The wear of parts of centrifugal pumps in natural conditions was also studied, and the dependences of wear on the characteristic dimensions and duration of their operation are given. The results of micrometering of the working parts of the pumps showed that the blades of the impellers along the length and width wear out unevenly both in size and shape. This is explained by the fact that when the hydroabrasive flow moves in the interblade space, the kinetic energy of solid particles and their local concentration increase due to an increase in the values of centrifugal and Coriolis forces along the radius of the impeller.

Design Strategy for Inlet Conditions of Supercritical CO2 Centrifugal Compressors

Abstract: To improve the aerodynamic performance and suppress the condensation in supercritical CO2 centrifugal compressors, a design strategy is proposed in this paper. The inlet compression factor and density are adopted to study the compressor performance and flow characteristics by solving three-dimensional Reynolds-averaged Navier-Stokes equations with condensable gas. The results indicate that in the range of operating conditions studied, increasing inlet compression factor or density, the condensation area will decrease. However, the pressure ratio will also decrease. By the means of decreasing inlet compression factor and increasing density, the inlet conditions alter from baseline conditions (7.69 MPa, 305.15 K) to optimization conditions (8.40 MPa, 305.54 K). The condensation area decreases by a large margin and the peak efficiency increases from 73.2% to 75.4%, while the pressure ratio remains unchanged. The design strategy provides a new idea for supercritical CO2 compressors to improve the performance and suppress the condensation at impeller inlet.