Impeller Volute Research Articles

Performance improvement of multi-blade centrifugal fan based on impeller outlet flow control

The impeller of the multi-blade centrifugal fan significantly impacts the fan's internal flow field and aerodynamic performance. To improve the axial flow distribution along the impeller and suppress the blade passage backflow at the impeller outlet of multi-blade centrifugal fans, a method of variable chord length blade design is proposed. Simultaneously, optimization models are established with static pressure and efficiency as objectives. By altering the control points of the Bezier curve, the leading-edge profile of the impeller is optimized. The results indicate that using variable chord length blades can expand the operating range of the multi-blade centrifugal fan. The maximum flow rate improvement reaches 10.6%. Significant enhancements in the aerodynamic efficiency of the multi-blade centrifugal fan are observed at low flow rates, with a maximum improvement of 4.9%. The variable chord length blade design method enables adjustment of the axial flow distribution at the impeller outlet to better match the impeller's flow requirements. This leads to increased outlet flow on both the shroud and hub sides of the impeller, consequently reducing the backflow area on both sides and improving the blade passage backflow phenomenon. Moreover, variable chord length blades facilitate a more uniform circumferential flow distribution at the impeller outlet, reducing the diversion pressure of the volute tongue, mitigating flow separation within the blade passage, weakening the interaction between the impeller and the volute tongue, and lowering energy losses in the impeller–volute tongue regions. Consequently, this enhances the aerodynamic performance of multi-blade centrifugal fans.

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

Aerodynamic design and acoustic effect study of key geometric parameters of a sirocco fan

A sirocco fan (forward-curved centrifugal fan), including impeller blades and volute, is designed, and the empirical value ranges of several significant design parameters are discussed and summarized fromthe perspective of both aerodynamics and practical structure. Unsteady-flow numerical simulation and radiated sound-field calculation by indirect boundary element method are combined to evaluate its aerodynamic and acoustic performances. Both the discrete noise source from the rotating impeller and broadband noise source from the volute are considered. Obvious flow separation occurs in the flow passage of impeller blades due to large angle of attack, and the tongue region is the major noise source area due to the small impeller-tongue gap. Therefore, parametric studies for blade installation angle and impeller-tongue gap are performed. Analyses of flow- and sound-field indicate that appropriate reduction of blade geometry incidence angle weakens the flow separation, thereby improving both the aerodynamic and acoustic performances, and reasonable increase of the impeller-tongue gap has a remarkable noise reduction effect for the major noise source area near the volute tongue. The optimized sirocco fan meets the requirement of the industrial project, i.e., the far-field A-weighted sound power level lower than 64.0 dB(A), and achieves larger volume flow rate and total pressure rise. The results also imply that fast steady-flow numerical simulation result is indicative of the acoustic performance to some extent if the acoustic evaluation is urgent. Furthermore, optimization of the key structural parameters in the stage of design is preferable in practical engineering, instead of taking follow-up noise reduction measures.

Pressure and Flow Rate Fluctuations in Single- and Two-Blade Pumps

Abstract A comparative study on the highly unsteady flow field in single- and two-blade pumps is performed. Stationary pump characteristics, as well as pressure and flow rate fluctuations, are presented. Wall pressure fluctuations were measured in the suction and pressure pipe as well as at several locations within the volute casing by piezoresistive transducers. Flow rate fluctuations were evaluated by a recently presented measurement system based on an electromagnetic flowmeter (Melzer et al. 2020, “A System for Time-Fluctuating Flow Rate Measurements in a Single-Blade Pump Circuit,” Flow Meas. Instrum., 71, p. 101675). Measurements were accompanied by three-dimensional (3D) flow simulations with the open-source cfd software foam-extend. A thorough grid study and validation of the simulation were performed. By a complementary analysis of measurement and simulation results, distinctive differences between both pump types were observed, e.g., flow rate and pressure fluctuation magnitudes are significantly higher in the single-blade pump. In relation to the respective mean values, flow rate fluctuation magnitudes are one order lower than pressure fluctuation magnitudes for both pumps. For the two-blade pump, fluctuations attenuate toward overload irrespective of the particular pump circuit, while they rise for the single-blade pump. 3D simulation results yield detailed insight into the spatially and temporally resolved impeller–volute interaction and reveal that the single-blade impeller pushes a high-pressure flow region forward in a way as a positive displacement pump, resulting in an inherently fluctuating velocity and pressure distribution within the volute.

Geometrical effects on performance and inner flow characteristics of a pump-as-turbine: A review

A pump-as-turbine is a hydraulic machine that can operate as a pump and turbine at the same time. Pump-as-turbine happens to be the most appropriate method for meeting the world’s energy demands, particularly in rural and isolated areas of a country. Furthermore, the operating cost of microhydropower systems is lower compared to conventional hydrodynamic turbines, but it requires high initial investment. Pump-as-turbine has been applied in many engineering fields such as irrigation, sewage, reverse osmosis, water distribution systems, farms, small pump storage power house, and pressure dropping valves. However, pump-as-turbine operates inefficiently at part-load due to lack of flow control device. In addition, the pump generates high flow instabilities in pump-as-turbine mode due to the shift of the best efficiency point toward higher head and discharge. This study extensively discusses the flow mechanism, modifications, and flow instabilities in the pump-as-turbine mode operation. First, the mechanism of the pump-as-turbine can be described as drawing out mechanical energy from the flow in the reverse mode. Since the energy drawn mainly depends on the major hydraulic components of the pump (impeller and volute), many studies have been conducted on the impeller and volute. It can be concluded that high amount of hydraulic losses is generated in pump-as-turbine mode operation. This can partly be attributed to the fixed geometrical parameters such as the stationary volute. To increase the usage of pump-as-turbine, it is very crucial to predict their performance in advance before manufacturing, which requires the understanding of the flow behavior as a result of geometrical parameters. In order to improve the energy conversion and understand the flow behavior in the centrifugal pump functioning as pump-as-turbine, the key geometrical parameters should be carefully designed. The designs of the main geometrical parameters do affect not only the hydraulic performance of pump-as-turbine but also the operational instability. The operational instability of hydraulic machines mainly depends on the pressure and the velocity fluctuation intensity generated within the flow passage as a result of the impeller–volute interaction. The magnitudes of the instabilities have the tendency to cause noise, vibration, harshness, and cavitation which reduces the life span of the hydraulic machine. Moreover, appropriate selection of the pump and unavailability of pump data contribute to the challenges faced. Finally, this review proposes specific solutions in terms of geometrical modifications and improvement of the computational design methods to handle the hydraulic losses faced during the pump operation; thus, this study can serve as a point of reference for a pump-as-turbine performance optimization.

Volute profile design of the squirrel cage fan based on a B-spline curve under space limitation

The cut volute profile is far and widely used in the squirrel cage fan to meet the space limitation of range hood systems. The cut volute profile often causes unreasonable impeller–volute interference and the aerodynamic performance of the fan to drop. A numerical model combined with the neural network and the genetic algorithm of a squirrel cage fan volute for a range hood is presented in this paper. The secondary non-uniform B-spline curve represents the volute profile variation law, and its control points are used as design variables to meet space constraints. The goal of global optimization is to maximize the efficiency and volume flow rate. As a result of the optimization, the internal flow loss of the fan is reduced compared with the prototype. The volume flow rate and efficiency are increased by over 4.4% in case of optimized volute than the original configuration of the volute.

Design and Verification of a Single-Channel Pump Model based on a Hybrid Optimization Technique

This paper handles a hybrid multiple optimization technique to concurrently enhance hydraulic efficiency and decrease unsteady radial forces resulting from fluid-induced vibration of a single-channel pump for wastewater treatment. A single-channel impeller and volute was optimized systematically by using a hybrid particle swarm optimization and genetic algorithm coupled with surrogate modeling. Steady and unsteady Reynolds-averaged Navier–Stokes analyses were conducted to optimize the internal flow path in the single-channel pump. Design variables for controlling the internal flow cross-sectional area of the single-channel impeller and volute in the single-channel pump were chosen to concurrently optimize objective functions with hydraulic efficiency and the unsteady radial forces resulting from impeller–volute interaction. The optimization results clearly showed that the arbitrary cluster optimum design considerably enhanced hydraulic efficiency and decreased the unsteady radial forces concurrently, compared to the reference design. Finally, the hydraulic performance of the optimized prototype model was verified experimentally. Then, it was proved that the proposed technique is a practical tool for designing a single-channel pump.

Three-objective optimization of a single-channel pump for wastewater treatment

The impeller and volute of a single-channel pump used for wastewater treatment were simultaneously optimized to improve the hydraulic efficiency and reduce unsteady radial force sources due to the impeller–volute interaction. Steady and unsteady Reynolds-averaged Navier–Stokes equations were solved with the shear stress transport turbulence model as the turbulence closure model using tetrahedral grids to analyze the internal flow in the single-channel pump. Five design variables related to the internal flow cross-sectional areas of the impeller and volute were selected to simultaneously optimize the hydraulic efficiency, the sweep area of the radial force during one revolution, and the distance of the mass center of the sweep area from the origin as the three objective functions. The response surface approximation model and genetic algorithm were employed to obtain three-dimensional Pareto-optimal solutions representing the trade-off between the efficiency and the radial force sources. The results of the three-objective optimization show that the representative clustered optimum designs enhanced the efficiency and reduced the radial force sources simultaneously in most cases, compared to the reference design. In addition, it was confirmed that the trade-off between the efficiency and the radial force sources clarifies with controlling the internal flow cross-sectional areas of the impeller and volute of the single-channel pump.

A Quantitative Evaluation Method for Impeller-Volute Tongue Interaction and Application to Squirrel Cage Fan With Bionic Volute Tongue

The impeller–volute tongue interaction strongly influences the aerodynamic performance of squirrel cage fan. To quantitatively evaluate the level of impeller–volute tongue interaction, we propose two parameters, i.e., recirculated flow coefficient and reversed flow coefficient based on a careful inspection of flow pattern near the volute tongue of a squirrel cage fan. Inspired by the good aerodynamic characteristics of owl wing, particular effort is made to develop a bionic design of volute tongue to improve the impeller–volute tongue match. The aerodynamic performances of both the squirrel cage fans with original volute tongue (OVT) and bionic volute tongue (BVT) are numerically and experimentally analyzed. The results show that, by employing the bionic design of volute tongue, the squirrel cage fan can achieve higher aerodynamic performance than that with OVT. Better match between impeller and volute tongue is obtained with smaller recirculated flow coefficient and reversed flow coefficient, validating the effectiveness of the proposed parameters to quantitatively evaluate the level of impeller–volute tongue interaction. In addition, the bionic design of volute tongue is beneficial for the improvement of flow quality and for the relief of abrupt pressure variation and axial nonuniformity of flow near the volute tongue. This work is helpful for a deep understanding of complex flow pattern in squirrel cage fan.

Numerical Studies of BPF Pressure Pulsation in Centrifugal Ventilators

There is a link between pressure pulsations in the centrifugal ventilator working cavity and its noise level on blade passing frequencies (BPF). They result from non-stationary hydrodynamic interaction between the impeller flow and volute casing. Pressure pulsations depend on quality of hydraulic profiling of ventilator. The amplification of pressure pulsations can happen due to matching of frequencies of oscillations with acoustic resonance frequencies. In ventilators the length of acoustic waves can be comparable to the size of the casing. Therefore, the variation of rotation speed, number of rotor blades, the fan installation in the ventilation system can substantially modify amplitudes of pressure pulsations due to the resonance inside the ventilator cavity. Various numerical studies of BPF pressure pulsation in ventilators are undertaken using the method and software package based on a representation of non-stationary motion of a compressible medium as a superposition of acoustic and vortex modes. In this case non-linear equations for unsteady vortex motion of an incompressible liquid are solved with a bigger time step. Wave equation relative to the pressure pulsations considering acoustic impedances on the borders of computational domain is solved by an explicit method. As a result, the whole processor time for both modes of oscillations is reduced and accuracy of prediction for the acoustical mode is improved.

Effects of the impeller–volute tongue interaction on the internal flow in a low-specific-speed centrifugal pump with splitter blades

To investigate the effects of the main blades and splitter blades interacting with the volute tongue on the internal flow in a low-specific-speed centrifugal pump, the Reynolds-averaged Navier–Stokes equation, coupled with SST k-ω turbulence model, is employed to simulate the transient turbulent flow in the whole flow passage. The numerical simulation results have been verified with the experimental measurements by comparing the head and efficiency. The pressure fluctuation caused by impeller–volute tongue interaction, including time–history and frequency characteristics, is calculated and analyzed at five monitoring points adjoining the impeller outlet and tongue, as well as the torque of a single main blade and a single splitter blade. After that, both the energy loss and vorticity distributions on the middle section are discussed when the impeller rotates to four circumferential positions relative to the cutwater. The results show that the maximum pressures at the monitoring points occur before the blades reach the closest circumferential position with respect to the cutwater, and the peak pressure near the trailing edge of splitter blades is larger than main blades. There is only one torque peak of a single blade in one revolution when the angle between the monitoring blade and tongue is about 15°. Additionally, the torque peak arises before the torque valley, but the pressure valley at monitoring points in the impeller comes earlier than the pressure peak. Both the energy loss and vorticity are enlarged around the volute tongue evidently after the blades pass by the cutwater, and the splitter blades produce more unsteadiness and energy dissipation than main blades.

Numerical Modeling of the Flow Inside a Centrifugal Pump: Influence of Impeller–Volute Interaction on Velocity and Pressure Fields

To analyze the centrifugal pump NS32 using numerical model and predicting the performance of a fluid flow in complexes geometry, we conduct several numerical simulation with different turbulence models. To evaluate the effect of turbulence model on the flow characteristics, the k-\({\varepsilon}\), SST and SST-CC turbulence models were tested. The simulations have been made using the multiple reference frames (MRF) technique to take into account the impeller–volute interaction. The computational domain is composed of two parts, a stator (volute) and a rotor (impeller). The impeller–volute interaction has been simulated using the frozen–rotor interface model for the steady-state calculations and the Rotor–Stator model for the unsteady ones. The distributions of velocity and pressure are computed using the Reynolds-Averaged Navier Stokes approach for a wide range of operating flow rates. To analyze the internal flow, simulation was carried out for several relative positions between the impeller blades and the volute tongue. In fact, the pressure fluctuations were numerically measured at five locations along the impeller and compared to experimental measurements. In addition, the unsteady pressure head evolution versus time was followed up. Then, an experimental validation of global and local characteristics of the pump was carried out.

Design Method for the Volute Profile of a Squirrel Cage Fan With Space Limitation

The uncontinuous volute profile (UVP) is widely used in the squirrel cage fan to meet the space limitation in the air conditioning system. However, it usually causes an obvious performance drop due to the unreasonable impeller–volute interaction. This paper employs two improved design methods, i.e., downsized volute profile (DVP) and partial flow volute profile (PVP), to enhance the aerodynamic performance of the fan installed in a limited space. Experimental results validate the positive effects of these two design methods on the aerodynamic performance. The results obtained by the flow simulation reveal that the pressure field inside the fan with the improved volute profiles is much more uniform than that with the UVP; thus, the improved volute profiles are beneficial for the increase of the fan pressure rise and the reduction of the flow loss. For the investigated fan, it is suggested that the design method of the DVP is more suitable for slight space limitation, while the design method of the PVP is more suitable for significant space limitation.

Research on Unsteady Pressure Fluctuation within the whole Flow Passage of a Fire Turbopump

The unsteady pressure fluctuation is one of the major factors affecting the operational stability of a fire turbopump. Based on the experimental operation conditions of the turbopump, the inner unsteady flow field in the turbopump is simulated by computational fluid dynamics (CFD), and the pressure fluctuations at the zones near the turbine suction chamber, the turbine impeller inlet, the turbine outlet and the interface of pump impeller/volute are investigated by time-frequency analysis methods. The results show that high pressure fluctuation can be observed near the interface of turbine impeller-guide vane and the interface of pump impeller–volute caused by rotor-stator interaction (RSI). Moreover, turbine pressure fluctuation frequencies are identified as the 14 times and 26 times of rotating frequency and the fluctuant amplitude depends on the guide vane inlet angle; whereas, pump pressure fluctuation frequencies are observed at the times of the blade passing frequency (BPF), while the frequencies higher than 10 times of BPF have less effect on the pump vibrations. The results of unsteady pressure pulsation could be used to guide the optimum design of the fire turbopump, which is in favor of obtaining more stable performance of the turbopump.

Centrifugal compressor performance assessment under different impeller tip clearance sizes from far to near stall conditions

Impeller tip clearance is a key parameter in design process of a centrifugal compressor which has influential effects on its aerodynamic and thermodynamic performances. Interaction of tip leakage flow with the main stream could be the major source for occurrence of stall phenomenon. In the present investigation, two impeller tip clearances of small and large sizes are investigated under different flow coefficients assigned to “design”, “low flow” and “high flow” conditions. Flow field is precisely simulated utilizing solution of the Reynolds-Averaged Navier-Stokes equations. Influence of the impeller stall on the volute flow field is studied. Structure of vortical flows within the impeller passages and volute are demonstrated in details. Numerical results showed that the flow within the volute becomes stall-prone while the flow within the impeller stalls. In contrast to the high flow case, the low flow condition was more prone for the stall occurrence. Performance tests were also conducted on Iran University of Science and Technology (IUST) centrifugal compressor test rig for validation of the numerical results.

Study of Pressure Fluctuations and Induced Vibration at Blade-Passing Frequencies of a Double Volute Pump

Strong impeller–volute interaction is a major source of high-pressure pulsations and vibration in high-powered pumps. The present study aims at establishing the foundation for correlating the pressure field with the vibration of the pump and identifying effective solutions to reduce flow-induced vibration in double volute pumps. Experiments were carried out on a model boiler feed pump stage to investigate the distribution of the pressure fluctuations inside the pump and pump vibration under different operating conditions. Critical zones of high-pressure fluctuations have been identified near the volute tongues, indicating strong impeller–volute interaction due to improper radial gap design. Vibrations closely follow the behavior of the pressure fluctuations under different operating conditions. High speeds combined with off-design flow rates result in higher pressure fluctuations inside the pump, which in turn excite vibrations of pump components. Measurements at discharge and suction pipes cannot represent the true behavior or the magnitudes of pressure fluctuations inside the pump, and hence cannot be correlated to pump vibration with fidelity. The clearance between impeller and volute tongues needs to be optimized by experimentation to minimize flow-induced pump vibration.

Unsteady Analysis of Impeller-Volute Interaction in Centrifugal Pump

An unsteady numerical analysis has been carried out to study the strong impeller volute interaction of a centrifugal pump with six backward swept blades shrouded impeller. The numerical analysis is done by solving the three-dimensional Reynolds Averaged Navier-Stokes codes with standard k-<TEX>${\varepsilon}$</TEX> two-equations turbulence model and wall regions are modeled with a scalable log-law wall function. The flow within the impeller passage is very smooth and following the curvature of the blade in stream-wise direction. However, the analysis shows that there is a recirculation zone near the leading edge even at design point. When the flow is discharged into volute casing circumferentially from the impeller outlet, the high velocity flow is severely distorted and formed a spiraling vortex flow within the volute casing. A spatial and temporal wake flow core development is captured dynamically and shows how the wake core diffuses. Near volute tongue region, the impeller/volute tongue strong interaction is observed based on the periodically fluctuating pressure at outlet. The results of existing analysis also proved that the pressure fluctuation periodically is due to the position of impeller blade relative to tongue.

The performance of a centrifugal fan with enlarged impeller

The influence of enlarged impeller in unchanged volute on G4-73 type centrifugal fan performance is investigated in this paper. Comparisons are conducted between the fan with original impeller and two larger impellers with the increments in impeller outlet diameter of 5% and 10% respectively in the numerical and experimental investigations. The internal characteristics are obtained by the numerical simulation, which indicate there is more volute loss in the fan with larger impeller. Experiment results show that the flow rate, total pressure rise, shaft power and sound pressure level have increased, while the efficiency have decreased when the fan operates with larger impeller. Variation equations on the performance of the operation points for the fan with enlarged impellers are suggested. Comparisons between experiment results and the trimming laws show that the trimming laws for usual situation can predict the performance of the enlarged fan impeller with less error for higher flow rate, although the situation of application is not in agreement. The noise frequency analysis shows that higher noise level with the larger impeller fan is caused by the reduced impeller–volute gap.

Prediction of Leakage Flow in a Shrouded Centrifugal Blood Pump

This article proposes a phenomenological model to predict the leakage flow in the clearance gap of shrouded centrifugal blood pumps. A good washout in the gap clearance between the rotating impeller surfaces and volute casing is essential to avoid thrombosis. However, excessive leakage flow will result in higher fluid shear stress that may lead to hemolysis. Computational fluid dynamics (CFD) analysis was performed to investigate the leakage flow in a miniaturized shrouded centrifugal blood pump operating at a speed of 2000 rpm. Based on an analytical model derived earlier, a phenomenological model is proposed to predict the leakage flow. The leakage flow rate is found to be proportional to h(α) , where h is the gap size and the exponent α ranges from 2.955 to 3.15 for corresponding gap sizes of 0.2-0.5 mm. In addition, it is observed that α is a linear function of the gap size h. The exponent α compensates for the variation of pressure difference along the circumferential direction as well as inertia effects that are dominant for larger gap clearances. The proposed model displays good agreement with computational results. The CFD analysis also showed that for larger gap sizes, the total leakage flow rate is of the same order of magnitude as the operating flow rate, thus suggesting low volumetric efficiency.

Experimental and numerical analyses of micro rotary shaft pumps

This paper presents experimental and numerical results obtained with micro rotary shaft pumps (RSP). Impellers with a diameter of 2.5 mm, different outlet widths and blade number were coupled with semicircular volutes with different eccentricities. Experimental data for every impeller–volute couple were reported and include the flow rate, head and overall efficiency. Different rotational speeds were tested up to 24 000 rpm, obtaining pressure increases up to 5.7 kPa and flow rates up to 80 ml min−1. The non-dimensional performance was also computed obtaining the maximum head coefficient of 0.49 and the maximum flow coefficient of 0.138. Furthermore, experimental data were compared with 3D time-dependent CFD simulations. The focus of the simulation was to study the flow field structure inside the impeller and in the volute. Moreover, CFD data allowed for the calculation of the hydraulic efficiency of the pump and for the impeller to highlight the stator rotor interference influence on the pump characteristics, as well as to show the distribution of losses inside the volute.