Volute Interaction Research Articles

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.

Effect of volute tongue angle on the performance and flow unsteadiness of an automotive electronic cooling pump

Automotive electronic cooling pump is the core component of the new energy vehicle cooling system, with the exclusive advantages of high efficiency and low vibration which will bring a broad market prospect. However, the rotor–volute interaction between impeller blades and volute tongue is a severe problem which can result in the performance degradation and unsteady flow fields of pumps. The influences of volute tongue angle on hydraulic performance and fluid stability are investigated in this study. The flow loss inside the pump is visualized by means of the entropy production theory, while the pulsations of pressure and radial force of the rotor are compared by unsteady computational fluid dynamics simulation. The results show that entropy production is an effective tool to visualize the loss distribution which allows accurate assessment of pump performance. Specifically, the pressure pulsation intensity near the volute tongue is larger and the main frequency of the radial force is the blade passing frequency. With the increase of volute tongue angle, the hydraulic efficiency under large flow conditions is improved, with an alleviated rotor–volute interaction intensity, and greatly reduced fluctuations of pressure and radial force. The main significance of this study is that it provides a new perspective to investigate the optimization design for automobile electronic cooling pumps.

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.

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.

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.

Numerical and Experimental Study on the PressureDistribution ina Volute of High-Speed Centrifugal Fan with Impeller- Volute interaction(English)

Numerical and Experimental Study on the PressureDistribution ina Volute of High-Speed Centrifugal Fan with Impeller- Volute interaction(English)

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.

Studies on the Influence of Various Blade Outlet Angles in a Centrifugal Pump when Handling Viscous Fluids

In this study the centrifugal pump performances with different blade outlet angles are tested when handling water and viscous oils as Newtonian fluids. Also, this study shows a numerical simulation of the three-dimensional fluid flows inside the centrifugal pump with different blade outlet angles. For these numerical simulations the SIMPLEC algorithm is used for solving governing equations of incompressible viscous/turbulent flows through the pump at different operating conditions. The k-e turbulence model is adopted to describe the turbulent flow process. These simulations have been made with a steady calculation using the multiple reference frames (MRF) technique to take into account the impeller- volute interaction. Numerical results are compared with the experimental characteristic curve for each viscous fluid. The results show that when the outlet angle increases, the centrifugal pump performance handling viscous fluids improves. This improvement is due to decrease of wake at the exit of impeller. Also the results show that the well-known jet/wake flow model is not found in the impeller simulations.

Aerodynamically Induced Radial Forces in a Centrifugal Gas Compressor: Part 2—Computational Investigation

Radial loads and direction of a centrifugal gas compressor containing a high specific speed mixed flow impeller and a single tongue volute were determined both experimentally and computationally at both design and off-design conditions. The experimental methodology was developed in conjunction with a traditional ASME PTC-10 closed-loop test to determine radial load and direction. The experimental study is detailed in Part 1 of this paper (Moore and Flathers, 1998). The computational method employs a commercially available, fully three-dimensional viscous code to analyze the impeller and the volute interaction. An uncoupled scheme was initially used where the impeller and volute were analyzed as separate models using a common vaneless diffuser geometry. The two calculations were then repeated until the boundary conditions at a chosen location in the common vaneless diffuser were nearly the same. Subsequently, a coupled scheme was used where the entire stage geometry was analyzed in one calculation, thus eliminating the need for manual iteration of the two independent calculations. In addition to radial load and direction information, this computational procedure also provided aerodynamic stage performance. The effect of impeller front face and rear face cavities was also quantified. The paper will discuss computational procedures, including grid generation and boundary conditions, as well as comparisons of the various computational schemes to experiment. The results of this study will show the limitations and benefits of Computational Fluid Dynamics (CFD) for determination of radial load, direction, and aerodynamic stage performance.

Numerical Simulation of Impeller–Volute Interaction in Centrifugal Compressors

A numerical procedure to predict the impeller–volute interaction in a single-stage centrifugal compressor is presented. The method couples a three-dimensional unsteady flow calculation in the impeller with a three-dimensional time-averaged flow calculation in the volute through an iterative updating of the boundary conditions on the interface of both calculation domains. The method has been used to calculate the flow in a compressor with an external volute at off-design operation. Computed circumferential variations of flow angles, total temperature, and pressure are shown and compared with measurements. The good agreement between the predictions and measurements confirms the validity of the approach.

NUMERICAL CALCULATION OF 2D, UNSTEADY FLOW IN CENTRIFUGAL PUMPS: IMPELLER AND VOLUTE INTERACTION

A numerical model is developed for calculating the two-dimensional, unsteady, incompressible and turbulent flow within the rotating impeller and stationary volute of an industrial centrifugal pump. The objective is the investigation and comprehension of the instantaneous behaviour of centrifugal pumps, aiming at the reduction of vibrations, radial forces and hydraulic noise. The computation is performed within a blade-to-blade streamtube for the impeller and a tube normal to the axis of rotation for the volute. The equations to be solved are the unsteady Reynolds-averaged Navier–Stokes equations along with the continuity equation and the unsteady κ–ϵ equations for turbulence modelling. The finite volume method is applied for space discretization and an implicit scheme for time discretization. A multidomain overlapping grid technique is used for matching together the relative flow field calculated within the rotating impeller and the absolute one calculated within the stationary volute. In this way the impeller and volute interaction is directly taken into account. The numerical model is validated for a centrifugal pump of N q=32 under design flow conditions. Comparisons between calculation and measurements show fairly good agreement.