Diffuser Blade Research Articles

Efficiency improvement and pressure pulsation reduction of volute centrifugal pump through diffuser design optimization

To investigate the effects of load distribution parameters of the diffuser vanes on the efficiency and pressure pulsation of the volute centrifugal pump, the diffuser shape was designed using an inverse design method, and an optimization method was proposed for the diffuser blade load distribution based on the combination of Latin hypercubic sampling, artificial neural network, and non-dominated sorting genetic algorithm-II. Steady and unsteady simulations were performed by solving the three-dimensional Reynolds-averaged Navier–Stokes equations using the shear stress transport k−ω turbulence model. The results obtained from Pearson correlation analysis revealed that the slope values Ks and Kh of the shroud and hub load distribution curves had the most significant effect on the pump head and efficiency. Compared with those of the original model, the efficiency and head of the optimized volute centrifugal pump under the design conditions increased by 3.8 and 3.5 %, respectively. The pressure pulsation intensities in the vaneless regions were effectively mitigated for the optimized volute centrifugal pump. The pressure pulsation coefficients at three times the diffuser vane frequency (3fDIF) reduced by 58.5 and 43.8 % at monitoring points M1 and M2, in the impeller outlet, respectively. The pressure pulsation coefficients at the impeller blade passing frequency (fBPF) reduced by 6.5 and 14.4 % at monitoring points M3 and M4 in the diffuser inlet, respectively. The results showed that the optimized diffuser improved the overall performance of the volute centrifugal pump, and demonstrated the feasibility of the optimization method.

Influence of internal flow structure on flow energy losses in a centrifugal pump with splitter blades using entropy generation theory

Centrifugal pumps are essential in various industrial applications, including renewable energy. To maximize the pump’s overall performance, estimating flow energy losses (FEL) is crucial. However, due to internal flow complexity, it is necessary to employ new methods and approaches to better understand FEL mechanisms. This study uses entropy generation theory to investigate the relationship between FEL and various flow patterns in all pump hydraulic components. Numerical simulations were conducted using a 3-dimensional incompressible unsteady flow at four different flow coefficients. The delayed detached eddy simulation (DDES) model was used, and the results showed good agreement with experimental data compared to the SST k-w model. Emphasis was given to the flow energy losses and the relative and absolute velocity distribution in the impeller and diffuser components at various flow coefficients. Flow energy losses primarily occur in the impeller (70%) followed by the diffuser (23%). Impeller losses are concentrated at the outlet region due to the wake-jet phenomena (28.6%), splitter blades region (15.3%), and impeller’s leading edge (LE) (10.7%). Vaned diffuser losses occur in the vanless zone (stator-rotor interaction) and near leading/trailing edges.Moreover, wall shear stress and the significant relative velocity gradient near the walls of the impeller and diffuser blades are the main contributors to the FEL in this region. This study provides insights into a better understanding of FEL mechanisms and highlights areas for improving pump performance.

Condensation mechanism and pressure fluctuation of a steam centrifugal compressor based on a non-equilibrium condensation model

In this paper, the condensation mechanism and pressure fluctuation of a steam centrifugal compressor are deeply studied based on a non-equilibrium condensation model. The wet steam model is generated to predict the flow characteristics and the condensation of the steam centrifugal compressor. The effect of different inlet temperatures on the steam condensation characteristics is deeply explored. Numerical results show that the steam condensation phenomenon on the high span surface is increasingly obvious, and the mass fraction of liquid steam first increases and then decreases with the increase in temperature. The droplet particle diameter and the droplet number gradually increase with the increase in temperature. It is also found that the blade loading on the impeller blade also becomes more unstable with the increase in inlet temperature. The amplitude spectrum of pressure fluctuation on the both sides of impeller blade and diffuser blade is analyzed through the fast Fourier transform. The pressure fluctuation in the flow channel becomes severe first and then becomes stable with the increase in temperature, which is well consistent with the variation trend of liquid mass fraction. The quantitative relationship between condensation strength and operating temperature is established to explore the variation trend essence of surface-average wetness fraction of different span surfaces at different inlet temperatures, which further reveals the condensation sensitivity to temperature at different blade heights. It is further found that the condensation strength on the low span surface and the average wetness fraction of steam condensation in the flow field increasingly decrease with the increase in inlet temperature.

Numerical Investigation of Rotor and Stator Matching Mode on the Complex Flow Field and Pressure Pulsation of a Vaned Centrifugal Pump

The match of rotor and stator blades significantly affects the flow field structure and flow-induced pressure pulsation characteristics inside the pump. In order to study the effects of the rotor and stator matching mode on the complex flow field and pressure pulsation of a centrifugal pump with a vaned diffuser, this paper designs three different vaned diffusers (DY5, DY8 and DY9) and uses the DDES (Delayed Detached Eddy Simulation) numerical method combined with structured grids to simulate the unsteady flow phenomena of the model pump under rated conditions. The results show that, under different rotor and stator matching modes, the pressure pulsation spectrum is dominated by the blade passing frequency and its harmonics. The matching mode of the rotor and stator significantly affects the time–frequency domain characteristics of the pressure pulsation inside the pump, and it is observed that the pressure pulsation energy of vaned diffusers with more blades is significantly smaller than that of fewer-blade vaned diffusers in comparison to the energy of the pressure pulsation at the blade passing frequency and within the 10–1500 Hz frequency band. Combined with the distribution characteristics of the complex flow field inside the pump, it can be found that increasing the number of vaned diffuser blades can reduce the energy of flow-induced pressure pulsation, improve the distribution of high-energy vortices in the interaction zone and stabilize the flow inside the centrifugal pump effectively.

Study on transient flow behaviors in a three-stage helico-axial multiphase pump under slug flow condition from wellhead

Oilfield recovery often has extreme flow patterns of slug flow, and its gas volume fraction (GVF) still fluctuates strongly after being buffered by a homogenizer. After entering the multiphase pump, it causes transient fluctuations in pump performance, which challenges the stable operation of the multiphase pump. This paper simulates the flow field in a three-stage multiphase pump using the Euler–Euler two-fluid model and the shear stress transport k-omega (SST k−ω) turbulence model with the buffered slug flow as the boundary conditions. The results show that the differential pressure and torque of each impeller vary with the fluctuation of the inlet gas volume fraction (IGVF) and the maximum fluctuation rate reaches 36.48% and 32.97%, respectively; the maximum fluctuation rate of axial force and radial force is 1.02% and 51.18%, respectively, and the buffered slug flow has limited effect on the axial force. The main factor of pressure pulsation is the fluctuation of GVF flow and the interaction of static and dynamic. The main frequency in the impeller is the fluctuation frequency of the GVF or the diffuser blade frequency. The main frequency in the diffuser is the impeller blade frequency and its double frequency. The fluctuation frequency of the GVF is the secondary frequency, and the amplitude is relatively stable.

Theoretical and experimental investigation on the stall inception of low-speed axial compressors with swept rotor blades

The effect of rotor blade sweep on the flow stability of low-speed axial compressors is investigated by means of theoretical model, numerical simulations and experimental measurements. Four compressors with forward or backward swept rotors are carefully designed by modifying the tip element location of the baseline rotor. Steady simulation results show that the designed aerodynamic sweep in this work hardly changes the pressure rise and efficiency characteristics of the compressor, which ensures the comparability between these compressors regarding flow stability. The developed stall inception prediction model based on global linear stability analysis and eigenvalue theory is employed to evaluate the stall boundary of compressors after blade sweep designs, and results indicate that the forward sweep slightly improve the flow stability, while the backward sweep has significant deterioration effect. What's more, the circumferential propagation frequency of the perturbation wave at stall onset changes little after the sweep design. The steady and dynamic measurements in experiments for different rotor blades verifies the theoretical conclusions and the prediction accuracy of the theoretical model. Through steady and unsteady flow field analysis, it is found that the forward sweep reduces the diffusion factor, elementary work and blade loading at the rotor tip region, while the backward sweep has the opposite effect and enhances the interaction between the tip leakage flow and the primary flow, which is deemed the contributors to their effect on flow stability.

Düşey Milli Eksenel Bir Pompada Zamana Bağlı Akışın Deneysel Olarak İncelenmesi

Due to the changes in the system characteristics, pumps may have to be operated far away from the design point, such as in part-load or over-load operating points. Operating the pumps far away from the design point may cause fluctuations in the flow. As a result of the fluctuations mechanical problems in the pump structure may occur. In order to overcome the problem, the operating characteristics of the pump must be determined at part load operating conditions as well as design point operating condition. In this study, flow inside a vertical shaft axial flow pump is investigated experimentally. The experimental setup is designed and constructed for the laboratory tests. The pump which is designed and manufactured is tested in the test setup. The performance of the pump is determined by measuring the flow rate, inlet and outlet pressures, rotational speed and power input of the pump. The part load and over load operating regions are determined. Pressure variations are measured at various performance points with the piezoelectric pressure transducer placed in between impeller and diffuser blade passage. Simultaneously, comparisons are made with the vibration spectrums obtained in the pump.

PATTERNS OF GAS FLOW IN A HIGH-PRESSURE CENTRIFUGAL COMPRESSOR

The development of three-dimensional modeling and analysis of the flow based on the solution of Reynolds-averaged Navier–Stokes equations allows to better determine the characteristics and flow parameters, but requires significantly more time spent on simulation and proof or verification of mathematical models in order to obtain minimal calculation errors. The aim of the work is to determine gas flow patterns in a high-pressure centrifugal compressor based on numerical methods for calculating the flow and to compare the integral characteristics with experimental data. The adequacy of the mathematical model with a displacement of the mass flow rate by 0.3 kg/s was confirmed. Nevertheless, the maximum mismatch of the determination of the total pressure ratio is equal to 8% in the zone of optimal values with flow displacement. The maximum error of determining efficiency is 9%. In the zone of optimal values, if the flow rate characteristic is shifted, the error of efficiency calculating does not exceed 2%. The pressure distribution along the impeller blades and the diffuser blades showed ways to optimize the blade shape to increase the compressor efficiency: there is an intersection of the lines for the optimal mode of the rotor blade; the splitter blade works in normal mode, but the distribution can be improved by changing the blade shape in the initial section; the intersection of the pressure lines for the optimal mode indicates the insufficient quality of the diffuser, which can be improved by changing the shape of the blade. For a more qualitative mathematical description of the flow patterns in the compressor, it is advisable to use the SST turbulence model, with a larger number of elements. The compressor characteristics were obtained numerically and the integral parameters of operation were determined. Keywords: high-pressure centrifugal compressor, numerical simulation, mathematical modeling, performances, adequacy

NUMERICAL SIMULATION OF GAS FLOW PATTERNS AND CHARACTERISTICS OF A CENTRIFUGAL COMPRESSOR

The design of compressors based on one- and two-dimensional flow calculations has reached the limit of development by achieving the maximum efficiency of devices. Further development is possible by conducting expensive experiments or by analyzing the results of the modern mathematical models of three-dimensional flow calculations based on the Reynolds-averaged Navier-Stokes equations. To improve the characteristics of the centrifugal compressor and improve the flow part with the subsequent change in the shape and location of the compressor impeller blades, threedimensional flow calculations were performed. Calculations were made using the Ansys CFX software with a student license. The effect of mesh on the integral flow characteristics is analyzed. There is a qualitative coincidence of the compressor performances, as well as gas flow patterns, and separation zones with experimental data. The research uses a sectoral approach to modeling. Calculations based on different turbulence models were compared and it was found that the models based on the "k – ε" model give practically identical results. Compared with the experimental data of the compressor, the Eddy Viscosity Transport Equation turbulence model showed a significant error in determining the total-to-total polytropic efficiency, this value is underestimated by more than 7 %. Due to an increase in the mass flow rate in the compressor, the velocity in the blade diffuser increases significantly and the flow separates from the blades. Based on the comparison of Mach number contours, in addition to flow separation from the diffuser blades, flow separation from the splitter walls and impeller blades are also observed, even at low mass flow rates. The influence of the sector approach on the calculation results and the mutual location of the impeller sector and the blade diffuser sector require further research, which will be the subject of further research.

Machine learning based on computational fluid dynamics enables geometric design optimisation of the NeoVAD blades

The NeoVAD is a proposed paediatric axial-flow Left Ventricular Assist Device (LVAD), small enough to be implanted in infants. The design of the impeller and diffuser blades is important for hydrodynamic performance and haemocompatibility of the pump. This study aimed to optimise the blades for pump efficiency using Computational Fluid Dynamics (CFD), machine learning and global optimisation. Meshing of each design typically included 6 million hexahedral elements and a Shear Stress Transport turbulence model was used to close the Reynolds Averaged Navier–Stokes equations. CFD models of 32 base geometries, operating at 8 flow rates between 0.5 and 4 L/min, were created to match experimental studies. These were validated by comparison of the pressure-flow and efficiency-flow curves with those experimentally measured for all base prototype pumps. A surrogate model was required to allow the optimisation routine to conduct an efficient search; a multi-linear regression, Gaussian Process Regression and a Bayesian Regularised Artificial Neural Network predicted the optimisation objective at design points not explicitly simulated. A Genetic Algorithm was used to search for an optimal design. The optimised design offered a 5.51% increase in efficiency at design point (a 20.9% performance increase) as compared to the best performing pump from the 32 base designs. An optimisation method for the blade design of LVADs has been shown to work for a single objective function and future work will consider multi-objective optimisation.

Topology optimization for fluid flow devices modeled through the Multiple Reference Frame approach

Fluid flow devices have been algorithmically designed through optimization methods, and this task is relatively complex for flow machines. Particularly, one recent development is the use of the topology optimization method for this task, which is capable of achieving possibly non-intuitive geometries and even auxiliary structures, such as splitter blades without ever imposing them as a condition for the design. The design of the rotating part of the rotor has already been previously considered. However, in the presence of stationary parts surrounding the rotor, such as diffuser blades, the fluid flow behavior may change, meaning that it may be interesting to consider this different dynamic in the design. One possible approach for this is the Multiple Reference Frame approach, which considers the fluid flow dynamics inside the rotor being computed in the rotating reference frame, whilst the fluid flow dynamics outside the rotor is being computed in the stationary reference frame. In particular, this implies the need for some changes in the topology optimization formulation, also impacting the choice of objective functions. Therefore, here the topology optimization method is formulated for the Multiple Reference Frame approach, and a new combination for the multi-objective function is proposed. The discrete design variable configuration from the Topology Optimization of Binary Structures approach is adopted with some adjustments to account for the Multiple Reference Frame approach. The fluid flow is chosen to be laminar or turbulent. Numerical examples are presented in 2D for the rotor-diffuser in order to consider some aspects that affect the overall topology optimization design.

Investigation of high-speed deep well pump performance with different outlet setting angle of space diffuser

As one of the important equipment for pumping groundwater, how to improve the operation performance of deep well pump has been a research hotspot. At present, most of the deep well pump hydraulic design research mainly focuses on the low speed condition, and there is still a lack of systematic research on the internal flow theory and design method of the high speed deep well pump. In this paper, numerical simulation is used to investigate the performance change law of high speed deep well pump under different space diffuser blade outlet setting angles, and the performance test of the design scheme model is used to verify the accuracy of numerical simulation. The hydraulic loss inside the space diffuser and the velocity moment at the outlet are quantitatively analyzed. The results shown that the outlet setting angle of 90° is a relatively optimal solution. Under the designed outlet setting angle, the hydraulic loss in the first-stage space diffuser decreases with the increase of the flow rate, and the average hydraulic loss in the space diffuser at all levels fluctuates between 16% and 20%. With the increase of the number of stages, the velocity moment at the outlet of the space diffuser also increases gradually, and the change trend of the velocity moment at the outlet of the first-stage space diffuser under different outlet setting angles is relatively consistent. This research can provide reference for the optimal design and application of high speed deep well pump.

Influence of Diffuser Vane Thickness on Centrifugal Compressor Performance

The structure of diffuser vanes has a significant influence on the performance of centrifugal compressors. To research the influence of diffuser vane thickness on the overall performance and internal flow condition of the centrifugal compressor. This paper takes a centrifugal compressor as the research object. By changing the diffuser vane thickness, and using three-dimensional fluid simulation technology to carry out simulation research. The results show that the thinner diffuser vanes can greatly improve the efficiency, flow rate and outlet temperature of the centrifugal compressor. For internal local fluid characteristics, thin diffuser blades have lower internal heat load. However, the local flow of fluid is not consistent with the change of vane thickness.

Numerical investigation on the unsteady vortical structure and pressure pulsations of a centrifugal pump with the vaned diffuser

To investigate the internal flow structures and the emanating pressure pulsations in a centrifugal pump with a vaned diffuser, the numerical method DDES (delayed detached eddy simulation) combined with a structured computational grid were employed to simulate the unsteady flow phenomenon of the model pump at the rated working condition. The vortical structures and pressure amplitudes at the blade passing frequency were mainly investigated. Results show that a significant difference, observed for pressure pulsations at the monitoring points from the suction side to the pressure side of the diffuser blade, and a high pressure amplitude is generated at the point near the suction side. The phenomenon is caused by the vorticity sheet interacting with the diffuser blade, and high turbulence is induced at the corresponding region leading to intense pressure pulsation. Evident attenuation of pressure pulsation is generated from the leading edge to the trailing edge of the diffuser blade. Significant vorticity sheets are formed around the trailing edges of the impeller and diffuser. Vortex street is generated at the diffuser trailing edge as indicated by the alternate shedding of positive and negative vortices and the horseshoe vortex is captured within the wake flow. Intense interaction is caused by the cutting impact of the volute tongue on the large scale vortices from the diffuser. The obtained results will contribute to a better understanding of unsteady flow and pressure pulsations in the centrifugal pump with a vaned diffuser.

A Methodology and Information System for Computing and Optimization of Impellers and Vanned Diffusers Geometry Parameters

Abstract The study aims to develop an information-computing complex for computer design of a centrifugal compressor with parallel calculation of stages and optimization of the geometric parameters of the impellers and the diffusers. The paper presents a universal methodology and computerized information system of the main geometry parameter determination and optimization of the centrifugal compressor impellers and vanned diffusers. Optimization of cross-sectional areas of the input and output channels of the impeller and diffuser blade channels is held using a gradient descent method by gas flowrate quadratic integral deviation criteria. The information-computing complex is built on the algorithm proposed by the authors and implemented as a computer program with a human-machine interface. Calculation data are written in the form of numerical arrays with the possibility of interpolating data and obtaining graphical dependencies.

Stall Behavior in an Ultrahigh-Pressure-Ratio Centrifugal Compressor: Backward-Traveling Rotating Stall

AbstractThis paper describes the stall mechanism in an ultrahigh-pressure-ratio centrifugal compressor, composed of a double-splitter impeller, radial diffuser, and axial diffuser. A model comprising all impeller and diffuser blade passages is used to conduct unsteady simulations that trace the onset of instability in the compressor. Backward-traveling rotating stall waves appear at the inlet of the radial diffuser when the compressor is throttled. Six stall cells propagate circumferentially at approximately 0.7% of the impeller rotation speed. The detached shock of the radial diffuser leading edge and the number of stall cells determine the direction of stall propagation, which is opposite to the impeller rotation direction. Dynamic mode decomposition is applied to instantaneous flow fields to extract the flow structure related to the stall mode. This shows that intensive pressure fluctuations concentrate in the diffuser throat as a result of changes in the detached shock intensity. The diffuser passage stall and stall recovery are accompanied by changes in incidence angle and shock wave intensity. When the diffuser passage stalls, the shock-induced boundary–layer separation region near the diffuser vane suction surface gradually expands, increasing the incidence angle and decreasing the shock intensity. The shock is pushed from the diffuser's throat toward the diffuser leading edge. When the diffuser passage recovers from the stall, the shock wave gradually returns to the diffuser throat, with the incidence angle decreasing and the shock intensity increasing. Once the shock intensity reaches its maximum, the diffuser passage suffers severe shock-induced boundary–layer separation and stalls again.

Effect of the number of blades on diffuser unsteady loss of centrifugal pump

Abstract In recent years, an unshrouded impeller is being developed for rocket turbopumps to reduce production costs and disk friction losses. However, the internal flow structure in a diffuser influenced by an impeller has not been clarified yet. In this study, we focused on the investigation of unsteady flow in turbopumps with unshrouded impellers and vaned diffusers by experiments and CFD. Furthermore, we investigated the effect of changing the number of blades of the impeller and diffuser on the unsteady losses in the diffuser. First, we measured the static pressure at the shroud side in the impeller and the velocity at the diffuser inlet and outlet. Second, we confirmed the accuracy of the CFD by comparing CFD results with experimental results. Third, we investigated unsteady losses in diffusers by CFD. We could confirm increased entropy at the suction surface and shroud side because of the tip leakage and the vortex. Finally, we changed the number of impeller blades or diffuser blades. In conclusion, the loss region at the suction surface and the high-pressure region at pressure surface in the unshrouded impeller were mixed and caused unsteady losses through the diffuser. And diffuser efficiency decreased because channel width in diffuser became narrower by the number of diffuser blades increasing.

Simulation and experiment research on liquid channel of diffuser blade by electrochemical machining

Aiming to solve the problems of the low electrolyte flow rate at leading edge and trailing edge and poor uniformity of the end clearance flow field during the electrochemical machining (ECM) of diffuser blades, a gap flow field simulation model was established by designing three liquid-increasing channels at the leading edge and the trailing edge of the cathode. The simulation results indicate that the liquid-increasing hole channel (LIHC) with an outlet area S of 1.5 mm2 and a distance L from channel center to edge point of 3.2 mm achieves optimal performance. In addition, the experiment results show that the optimized cathode with liquid-increasing hole channel (LIHC) significantly improves the machining efficiency, accuracy, and surface quality. Specifically, the feed speed increased from 0.25 mm/min to 0.43 mm/min, the taper decreased from 4.02° to 2.45°, the surface roughness value of the blade back reduced from 1.146 to 0.802 µm. Moreover, the roughness of the blade basin decreased from 0.961 to 0.708 µm, and the roughness of the hub reduced from 0.179 to 0.119 µm. The results prove the effectiveness of the proposed method and can be used for ECM of other complex structures with poor flow field uniformity.

Improvement of Unstable Flow in a Low Solidity Cascade Diffuser of Centrifugal Compressor by Multi-Objective Optimization

A compressor for turbochargers is commonly required improving efficiency and expanding the operating flow rate range. Though an aerofoil type diffuser shows better pressure recovery than conventional vaneless diffuser, it is difficult to design the aerofoil type diffuser under conditions of wide change of the flow angle. An innovative design of a Low Solidity circular cascade Diffuser (LSD) was proposed for flow range enhancement of cascade diffuser¸ and an interesting function of the LSD is introduced. At small flow rate conditions, low energy fluid near the diffuser side wall spread between the diffuser blade, and low energy fluid moves to the leading edge of the adjacent blade, then low energy fluid merged with main flow and suppress the flow separation. The phenomena spread to circumferential direction, and whole of the LSD blades show high stability for separation under a large angle of attack. In this study, LSD is designed for compressors of turbocharger by using a Genetic Algorithms (GA) with meta-model of an Artificial Neural Networks (ANN). The final goal of this study is to optimize the LSD with having secondary flow effect under low flow rate conditions.

Numerical and experimental study in pressure pulsation and vibration of a two-stage centrifugal pump under cavitating condition

Instantaneous cavitating turbulent flow in a two-stage centrifugal pump with diffuser was simulated using a hybrid RANS/LES model and rotating corrected-based cavitation model in this paper. The predicted results of numerical simulation were in good agreement with the experimental results. The mechanism of pressure pulsation in the two-stage centrifugal pump was discussed. Some representative main frequencies of pressure pulsation such as main blade passing frequency, sub-blade passing frequency and intersection frequency of impeller blade and diffuser blade were analyzed systematically. Uncertainty estimation was used to ensure the accuracy of experimental results and it was also used to analyze the variation of pressure pulsation and vibration signals at different positions with the intensification of cavitation degree in the centrifugal pump. According to the results of uncertainty estimation, the center frequency of 1/3 octave band and the root mean square method were used to evaluate the energy change of the pressure pulsation signals and vibration signals at different frequency bands as the cavitation number decreases. The characteristics of pressure pulsation and vibration signals at different positions were analyzed in different frequency bands.