Front Shroud Research Articles

Effect of Trimmed Rear Shroud on Performance and Axial Thrust of Multi-Stage Centrifugal Pump With Emphasis on Visualizing Flow Losses

Abstract Multi-stage centrifugal pumps are frequently used in high-lift applications and consume considerable energy, but suffer from poor performance and large axial force. The rear shroud of impeller is trimmed for reducing axial thrust, but this degrades performance. This study analyzes performance degradation and optimizes performance and axial force. Experiments and simulations are conducted on different ratios of rear shroud to front shroud (λ). Total pressure losses are calculated, and flow losses are visualized using the entropy generation method. Both measured and simulated performances decrease as the rear shroud is trimmed. Designs with different λ meet the head coefficient requirement of 1.1. However, λ of 0.86 has the best efficiency of 42.7%, λ of 0.83 reaches 42.5%, λ of 0.8 shows the lowest efficiency of 39.9%. Efficiency in the middle channel improves as the rear shroud is trimmed, but this cannot offset increased losses in the impeller and rear side chamber. Entropy production is exacerbated in the axial passage between impeller and rear side chamber due to the collision between impeller-driven flow and pressure-driven backflow. When λ is reduced by 0.03, axial thrust drops by 7%. To compromise between performance and axial thrust, λ should be designed at 0.83.

Improving air-water two-phase flow pumping in centrifugal pumps using novel grooved front shrouds

The present investigations aim to improve the gas-liquid two-phase transport in centrifugal pumps using a novel front shroud design with macroscopic grooves. This increases the secondary flow strength and the two-phase mixing, boosting the performance. A total of 23 different circumferential and radial groove profiles were numerically investigated to identify the best configuration leading to the highest mixing efficiency. Three different loads were considered, i.e., part load, optimal point, and overload. Additionally, the performance of the novel designs was compared with that of the established alternatives, involving two different clearance gaps and/or an inducer. While circumferential grooves already lead to a slightly improved specific delivery work, radial grooves improve noticeably the pump efficiency and deliver a very high two-phase mixing compared to other traditional pump configurations. Under conditions of optimal loading, the utilization of circumferential grooves led to a phase mixing enhancement of approximately 19.5%, whereas the implementation of radial grooves exhibited a notable improvement in mixing efficiency by 64.8% compared to the standard gap. The radial design R14 is superior to all other designs regarding efficiency and phase mixing. It is therefore recommended for transporting gas-liquid two-phase flows.

Swirl Brake Design for Improved Rotordynamic Vibration Stability Based on Computational Fluid Dynamics System Level Modeling

Abstract The accurate characterization of compressor rotordynamic coefficients during the design phase reduces the risk of subsynchronous vibration problems occurring in the field. Although rotordynamists extensively investigate discrete compressor components (such as seals and front shrouds) to tackle instability issues, integrated or system-level analysis of compressor rotordynamics is very sparse. In reality, the impeller, eye-labyrinth seal, and the front shroud heavily influence one another; and the collective dynamic behavior of the system differs from the sum of the dynamic behavior of isolated components. A computational fluid dynamics (CFD)-based approach is taken to evaluate the dynamic behavior of the system as a whole. The geometry and operating conditions in this work are based on the recent experimental study of Song et al. (2019, “Non-Axisymmetric Flows and Rotordynamic Forces in an Eccentric Shrouded Centrifugal Compressor—Part 1: Measurement,” ASME J. Eng. Gas Turbines Power, 141(11), p. 111014. 10.1115/1.4044874) on centrifugal compressor. The commercial CFD code cfx 19.0 is used to resolve Reynolds-averaged Navier–Stokes equations to quantify the eye-labyrinth seal and front cavity stiffness, damping, and added mass. The entire compressor stage is modeled to uncover the coupled behavior of the components and assess the stability of the whole system instead of just discrete components. In the current work, three CFD approaches, namely quasi-steady, transient static eccentricity, and transient mesh deformation techniques are studied and benchmarked against analytical and experimental results from the literature. Having established the efficacy of the proposed approach, four types of swirl brakes are proposed and analyzed for stability. The novel swirl brakes create negative swirls at the brake cavities and stabilize both the front shroud and the eye-labyrinth seal simultaneously.

Analysis of the axial force distribution characteristics of multistage pumps and its correlation with hydraulic property

As the centrifugal pump is running, the fluid usually flows into the impeller along pump shaft, and the fluid flows out radially by the force of the impeller. The force is mutual, so the impeller is also subjected to the reaction force of the fluid, but the distribution of this force on the blades is uneven. In addition, the front and rear shrouds of the impeller are asymmetric, which are the main causes of axial force. This paper adopts numerical calculation method studying the mechanism of axial force of impeller at all stages of multistage pump at various working conditions, and exploring the formation mechanism of shroud pressure differential force and blade twisting axial force and its variation laws of similarities and differences, analyzing the steady state and transient characteristics between axial force and hydraulic property of double-casing multistage pump. The results show that the rotational angular velocity of the fluid in the front and rear pump chamber at each stage impeller is distributed along the axial direction in three regions, the regions are pump body boundary layer, core region, and impeller boundary layer. The working surface and back surface of the blade twist have the high and low axial force area, and its distribution is staggered, at the same number of stages, the greater the flow rate, the smaller the blade twisting axial force. The shroud pressure differential force with the increase of impeller stages presents a linear increasing trend, conforms to the principle of linear superposition of cover pressure differential force. The total axial force pulsation of multi-stage pump is related to the number of secondary impeller blades, its primary frequency coincides with the secondary impeller blade frequency, increasing the flow rate can reduce the multi-stage pump axial force pulsation amplitude. The pulsation period of single-stage impeller head and efficiency are related to the number of impeller blades, the smaller the number of impeller stages, the stronger the pressure dynamic, and static interference effect of the impeller inlet and outlet. Rotation of the secondary impeller causes dynamic and static interference, which is the main reason for the pulsation of the axial force coefficient in double-casing multistage pumps, the pulsation intensity is related to the periodic generation and shedding of the blade vortex. The results of the study can be used as a reference for optimizing the axial force of double-casing multistage pumps.

Optimal design and performance improvement of an electric submersible pump impeller based on Taguchi approach

Electric submersible pump (ESP) is the core artificial lift equipment to pump production oil from underground or deep sea to the surface. Its energy efficiency significantly affects global oil market and energy consumption. To explore the effects of the impeller meridian profile on the hydraulic performance, a typical multi-stage ESP with medium specific speed was taken as the research object. Based on the statically determinate control of the shroud and hub profiles, eight parameters of the impeller meridian profile were selected as the key factors. By taking head and efficiency as optimization targets, 27 schemes were designed according to the Taguchi approach. The effect analysis method was employed to determine the primary and secondary order of the parameters. The linear relationship between the meridional parameters and the optimization target was analyzed based on regression analysis. The results show that the design of the intersection line of the front and rear shrouds in the impeller meridian has great effects on the ESP performance. The optimal model shows a significant improvement on both of efficiency and head compared with the original model. The head increases 3.5% and the efficiency increases 6.1%. This study provides new inspiration to optimize the hydraulic design of ESPs to achieve higher efficiency and lower energy consuming.

Tonal noise of voluteless centrifugal fan generated by turbulence stemming from upstream inlet gap

Volutes for radial-flow turbomachines (e.g., centrifugal fans and pumps) are spiral funnel-shaped casings that house rotors. Their function is to guide the flow from rotors to outlets and maintain constant flow speeds. Under specific conditions, however, volutes are removed (termed voluteless) to reduce flow losses and noise. In this paper, a generic voluteless centrifugal fan is investigated for the tonal noise generation at an off-design operation point. In contrast to typical tonal noise sources induced by the fan blades, we find out that another predominant source is the turbulence stemming from the clearance gap between the fan front shroud and the inlet duct. The turbulence evolves along with the front shroud and is swept downstream to interact with the top side of the blade leading edge. An obvious additional tone is observed at 273 Hz other than the blade passing frequency (BPF0) and relevant harmonic frequencies. By coarsening the mesh resolution near the inlet gap and front shroud in the simulations, we artificially deactivate the gap turbulence. Consequently, the tone at 273 Hz disappears completely. The finding indicates that the interaction between the gap turbulence and blades accounts for the tone. As the gap turbulence exists near the front shroud, this rotating wall introduces rotational momentum into the turbulence due to skin friction. Hence, this tonal interaction frequency is smaller than BPF0 with a decrement of the fan rotation frequency. To the authors' knowledge, this is the first time that voluteless centrifugal fans are studied for the gap-turbulence noise generation.

Numerical Investigation of Erosive Wear of a Centrifugal Slurry Pump Due to Solid–Liquid Flow

Abstract Centrifugal slurry pump designed for handling solid–liquid flow experiences performance reduction and shorter service life due to uneven localized erosive wear of the wetted parts. In this work, three-dimensional (3D) unsteady numerical modeling of a centrifugal slurry pump with Eulerian–Lagrangian approach coupled to the erosion model has been performed to predict the erosive wear of the pump components namely, casing and impeller. The erosion model developed to predict the erosion of the pump components of high chromium white cast iron (HCWCI) is employed, and the erosion rate distribution along the complete length and width of the casing and impeller blade surfaces namely, pressure side, suction side, front shroud, and back shroud, is determined. The numerical results showed good agreement with the experimentally measured erosion of the pump casing. It has been found that the erosion of the casing and impeller is non-uniform along the length and width. The zone of higher erosion is at the centerline and the back side of the casing, whereas, for the impeller, it is on the pressure side near the leading edge. The variation in the operating flowrate and particle size greatly influenced the material removal rate and the zone of higher erosion for the casing and impeller blade surfaces.

Influence of blade inlet angle on the performance of a single blade centrifugal pump

Single blade centrifugal pump is suitable for transporting sewage water with large obstacles in diameter, which is required to achieve high performance. The blade inlet angle is a parameter that affects the performance of the single blade centrifugal pump. However, the selection of blade inlet angle is frequently based on experiences and demonstrates certain arbitrariness. Therefore, six impellers with different blade inlet angles are designed using ANSYS Bladegen and NX software. These impellers are categorized into Groups 1 and 2. The blade inlet angle of the impellers in Group1/Group2 increases/decreases from the front shroud to the rear one, respectively. Subsequently, the numerical simulation is carried out to investigate the effect of the blade inlet angle on the performance of the single blade pump. The blade inlet angle has more obvious influence on the head, efficiency, and shaft power for the impellers in Group 1 than those in Group 2. The lowest pressure is negative for one of the impellers in Group 1. Moreover, an optimum blade inlet angle improves the pump performance. In addition, the alternating load is small on the blades of the impellers in Group 2. The present results are helpful in designing the single blade centrifugal pump and improving its performance.

Effects of hydraulic loads and structure on operational stability of the rotor of a molten-salt pump

The present study aims to evaluate the operational stability of an impeller pump transporting high-temperature molten salt. A numerical strategy incorporating the computational fluid dynamics (CFD) technique and finite element analysis was designed. The coupling between fluid flow, temperature and structure was enabled. Effects of the flow rate of molten salt on mechanical properties of the rotor were investigated. The results show that pressure distributions remain similar at the flow rates inspected. Along the shaft, temperature decreases gradually from the impeller end towards the bearings. The maximum Von Mises stress in the impeller arises at the junction between the blade and the front shroud and varies inversely with the flow rate. The deformation of the impeller is non-axisymmetric and is minimized at the design flow rate. The modal shape manifests quadratic patterns at high orders of modes. The double-volute pump structure was proposed and validated. It is evidenced that radial hydraulic forces exerted on the impeller are reduced relative to the single-volute scheme. The impeller deformation is uniformized and the maximum Von Mises stress in the pump rotor decreases.

Effect of molten salt properties on internal flow and disk friction loss of molten salt pump

Computational fluid dynamics is used to study the effect of temperature on flow structure and disk friction loss for different working fluids in a high temperature molten salt pump, which is used for concentrating solar power, the velocity profile and pressure distribution in the first stage of the pump model and the effect of the fluid property on the ring leakage, disk friction loss as well as the shear stress distribution on shroud are analyzed for the pure water and the molten salt with temperature 300?C and 565?C respectively. The main findings can be concluded as: the working fluids have little effect on pump performance and internal velocity distribution whereas the pressure of the flow field would increase with the fluid density, with the increase of the fluid viscosity, the shear stress inside the ring also increases and the total leakage can be eliminated evidently, the increase of the fluid density and viscosity show the significant responsibility for the disk friction loss, in which the fluid viscosity also increases the disk friction loss, and the viscosity is one of the most influential factors for the shroud shear stress and it can be observed that the shear stress on front shroud is higher than that on the rear shroud. It is believed that the present work can deep the understandings of the fluid structures inside the molten salt pump, which can provide some guidelines to improve the pump performance and optimize the pump structure.

Multi-Parameter Optimization and Analysis on Performance of a Mixed Flow Pump

A mixed flow pump with guide vanes was chosen as research model in this study, and eight parameters of the impeller were selected as optimization variables, including blade outlet inclination angle, blade wrap angle at hub, blade inlet angle and outlet angle at middle stream line, blade outlet width, front shroud inclination angle, hub inclination angle and vane number. Firstly, orthogonal experimental method and CFD numerical simulation method were used to produce samples, then the RBF neural network was adopted to establish the performance prediction model as the objective function, multi-island genetic algorithm was used for solving the objective function at last. Based on all the above, a method of multi-parameter optimization method on energy performance of mixed flow pump without changing the nominal diameter of impeller outlet was proposed and then verified by experiments. By this method, the pump head and efficiency at the design point of the model pump were increased by 11.5% and 4.32%, respectively. Meanwhile, the peak value of pressure pulsation coefficient at pump inlet, impeller outlet, guide vane outlet and pump outlet all decreased obviously, by a maximum decrease of 62.9%. Compared to the original model, the static pressure in the optimization model increased by 30kPa and the gradient of static pressure distribution after optimization becomes larger and more uniform. The turbulent energy intensity at the impeller outlet was reduced by 0.2m2/s2. The pressures at the 60% blade position and 80% blade position both increased by nearly 65kPa and the pressure decreased by 50kPa at the blade pressure side.

Mechanism of the Occurrence of Rotordynamic Fluid Forces on a Closed Type Centrifugal Impeller in Whirling Motion

Rotordynamic fluid forces and a mechanism of their occurrence were examined in experiments and computations for a closed type centrifugal impeller in whirling motion. The rotordynamic fluid force on a front shroud was a main component of the rotordynamic fluid force. In a clearance between the front shroud and a casing, velocity disturbances were caused by an eccentricity of the impeller and a squeeze effect due to the whirling motion of the impeller. Appling the Bernoulli equation to disturbed swirling flow in the clearance in a relative coordinate fixed on the whirling motion, the pressure disturbance which generated the rotordynamic fluid force could be reasonably explained.

Numerical analysis of flow structure and energy loss in an impeller side chamber of a molten salt pump

The internal flow structure and the energy loss in the first stage impeller side chamber of a molten salt pump for solar thermal power generation were investigated numerically. The flow field in the model pump was simulated based on the RANS equation using the standard k-? turbulence model. The results indicate that the rotating speed of core flow in the front impeller side chamber is higher than the tangential velocity at the maximal radius of the front shroud. However, the core flow in the rear impeller side chamber gives an opposite trend. Meanwhile, the radial velocity at the boundary-layer separation point on the front impeller side chamber stationary wall decreases initially and then increases with the radius while it only decreases in the rear impeller side chamber. For the energy loss, the percentage of the disk friction loss to total energy consumption reduces as the flow rate increases, while the absolute value of disk friction loss on the front shroud keeps almost constant and the loss on the rear shroud decreases with the increasing flow rate.

The Fluid Force on a Whirling Columnar Rotor

In the operation of hydro turbines and pump, self-excited vibration can occur due to fluid force which is generated as a response to the vibration and is called rotordynamic fluid force. The tangential component of rotordynamic fluid force has large impact on the stability of rotors. Characteristics of the tangential fluid force acting on a whirling columnar rotor which is modelled on the front shroud of a Francis turbine during self-excited vibration were investigated in computation in the present study. The angular velocity of the whirling motion of the rotor and the tangential force could be normalized by the axial velocity of axial leakage flow through the clearance between the rotor and the casing and the square of it, respectively. In the range of large whirling velocity, the tangential force was caused by a pressure distribution in the case without axial leakage flow. In the range of small whirling velocity, it is known that the tangential force is generated by the inertia of axial leakage flow. In the range of middle whirling velocity, the tangential force was found to be caused by both effects of whirling motion of the rotor in static fluid and the inertia of axial leakage flow. The pressure distribution without axial leakage flow was due to pressure loss in the wake of the rotor in addition to effects of shear stress and discharge from /suction into the clearance.

Theoretical Estimates of Rotordynamic Fluid Forces on a Front Shroud of Francis Turbine Caused by Leakage Flow

Theoretical Estimates of Rotordynamic Fluid Forces on a Front Shroud of Francis Turbine Caused by Leakage Flow

Effect of innovative circular shroud fences on a centrifugal fan for augmented performance - A numerical analysis

This paper presents the influence of circular front and back shroud fences on the performance of a backward swept centrifugal fan impeller handling air. The analysis is carried out to determine the main characteristics of the fan i.e. the variation of head and theoretical efficiency for various flow coefficients. The circular fence size is optimized parametrically by varying its diameter and the location on the shroud surface. The effect of the shroud fences on the flow field was analyzed for the fences placed on both front and back shroud surfaces of the impeller separately. The numerical simulation is carried out using an appropriate k - e turbulence model. The relative flow inside the impeller passages is modeled using the standard sliding mesh technique. The numerical results for the base model (i.e. without the fence) are validated against experimental results obtained from the test rig built specially for validation study and are found to have good agreement. It is found from the analysis that the average percentage increase in head coefficient is significant and is about 2 % higher as compared to the base model for the optimized geometrical configuration of diameter ratio and radial fence location as determined in the study. The optimized geometrical configuration also yields a higher theoretical efficiency of about 2.3 % corroborating the improvement in head coefficient with respect to the base model. Hence the efficacy of optimally placed circular fence on the performance of centrifugal fan is established in this numerical study.

Ansys CFX numerical study of stages centrifugal compressor with low-flow rate coefficient

The article presents results of applying the methods of computational fluid dynamics for model low-flow rate stages of centrifugal compressors with flow rate coefficient F = 0.028. The computational domain of a model centrifugal compressor for CFD-simulation consists of the following elements: inlet chamber, impeller, vaneless diffuser, return channel, outlet chamber, shaft seal labyrinth, front and back shroud leakage. Full-scale experimental studies were conducted to model stage 028 in air at an inlet pressure of p* = 1 atm. Numerical research for stage 028 held with flow rate coefficient F=(0.019-0.046) for three variants trailing edge of the impeller. According to the results of numerical research are constructed performances of stages centrifugal compressor and conducted verification of results. Estimated discrepancy between the results of numerical researches on the model with shaft seal labyrinth and without shaft seal labyrinth.

Fluid-structure interaction analysis of an impeller for a high-pressure booster pump for seawater desalination

A High-pressure booster pump (HPBP) is an essential piece of equipment in a Seawater reverse osmosis (SWRO) system. As the corerotating component in the HPBP, the impeller operates extensively in a high-pressure and corrosive environment and its work status directly affects the reliability of the pump device. The vibration characteristics of the rotor were analyzed using fluid-structure interaction theory to determine the characteristics that would ensure the long-term safe operation of the HPBP. The stress and deformation analysis was performed on a partitioned solution for an impeller in a moving fluid, and the modal analysis of the impeller was conducted in still fluid based on a monolithic solution. The influence of the impeller shroud thickness on the resulting vibration characteristics was investigated by using three modifications of the impeller. A comparison of the results with the initial impeller geometry was then carried out under partial load operations. Three commonly used materials for an impeller were also evaluated. The three-dimensional turbulent flow was modeled utilizing the SST k-ω turbulence model, and the numerical results were verified by the experimental data. The results show that natural frequency of the 20CrMnTi is the highest among the three materials for each order mode, followed by 00Cr17Ni14Mo2Ti (316L) and HT250Ni2Cr. Increasing the rear shroud thickness would result in a notable reduction in its deformation. Evidently, the thicker the front and rear shrouds, the lower the shroud deformations. Among the three operating points, the displacement fields of the impeller were quite akin. An outward displacement growth was observed within the impeller hub to the outer diameter, thereby leaving both shrouds with a local maximum on the blade passage. Additionally, higher equivalent stress values were observed at the junction between the blade and the shroud. These results reveal the deformation and stress affecting the impeller, which then enables identification of and provides specific theoretical guidance for the optimization of the structural design of the pump.

Numerical investigations on effect of wear-ring clearance on performance of a submersible well pump

A typical submersible well pump was investigated in this article. The whole flow field of submersible well pump was numerically simulated by computational fluid dynamics software. The influence of clearance of wear-rings on the external characteristic and internal flow field was analyzed through comparing the calculation results with experimental results. The result of the numerical simulation shows that changing clearance of front wear-ring has a greater impact on pump performances than changing clearance of back wear-ring, and the head and efficiency of pump decrease with the increase in the size of clearance. Especially when the size of clearance is larger than 0.5 mm, decreasing becomes more obvious. When the front and back wear-ring size of the clearance comes to 1.0 mm, the efficiency decreases from the highest point of 75.31% to 65.44% at rated flow, and the head of pump decreases about 3.5 m. When the size of clearance is 0.2 mm, reverse-flow will appear in the front shroud cavity of the impeller, and leakage from back wear-ring through the balance hole into the impeller, which has a little influence on the flow field of the impeller inlet.

Numerical Analysis of Stress and Deformation of Impeller in the Mixed Flow Pump Based on Fluid-structure Interaction

To improve the operational reliability of mixed flow pumps, the two-way coupling fluidstructure interaction method is applied to investigate stresses and deformations of the impeller. The Reynolds-averaged Navier–Stokes equation, coupled with the SST k-ω turbulent model, is solved in the fluid domain by using ANSYS CFX, while transient structure dynamics in the structural domain are calculated with the finite element method. The accuracy of the numerical results has been verified by experimental pump performance. The results show that the flow rate definitely has a noticeable effect on both deformations and stresses. With the flow rate increasing, the impeller deformation decreases, as well as the stress, which is completely different from centrifugal pumps, but similar to axial pumps. Moreover, a local maximum deformation occurs in the middle of blade inlet, and the maximum stress of the entire impeller fluctuates periodically. On the same shroud, the stress on the suction side is higher than the pressure side along the intersection path; and on the same side, the mean stress on the rear shroud is larger than the front shroud. This study can help understand the distribution of both deformations and stresses in the impeller and provide guidance for improving the operation safety of mixed flow pumps.