Volute Tongue Research Articles

Numerical investigation of clocking effect on a centrifugal pump with inlet guide vanes

Purpose The paper aims to investigate the clocking effect on a centrifugal pump with inlet guide vanes (IGVs). Design/methodology/approach The paper uses a computation fluid dynamics (CFD) framework to solve the unsteady flows in a centrifugal pump with inlet guide vanes. The relative position between the stationary vanes and the stationary volute tongue is defined as the clocking position when IGVs inside the suction pipe rotate along the circumferential direction. Findings The results show that clocking positions have little effect on the pump head and efficiency, however their influences are obvious for the pressure fluctuation and flow field in the centrifugal pump. The maximum difference of pressure amplitude at dominant frequency reach up to 28% on the monitoring point V8 at different clocking positions under design flow rate. For the large flow rate, the clocking effect on flow field and pressure fluctuation in centrifugal pump is similar to that of design flow rate. However, the clocking effect is nearly negligible at partial flow rate, because there are reverse flows around the tongue tip and obvious vortexes forming and developing in the impeller. Those complex phenomena interacting in the centrifugal pump make the clocking effect less evident. Originality/value The numerical investigation reveals the clocking effect on a centrifugal pump with inlet guide vanes, which also valuable for the stable operation and optimal design of centrifugal pumps.

Numerical and experimental investigations of the unsteady aerodynamics and aero-acoustics characteristics of a backward curved blade centrifugal fan

A numerical study of the aerodynamic and aeroacoustic behaviors of a backward curved blade centrifugal fan was conducted under two important flow conditions: BEP and 1.3×BEP. Three-dimensional numerical simulations of the complete unsteady flow field for the whole impeller-volute configuration were used to determine the aeroacoustic sources. To locate the unsteady flow and perturbations, the near field wall pressure fluctuations at different strategic points on the volute were computed using the URANS approach. Thus the intensities and positions of the aeroacoustic sources were identified by analyzing frequency spectra. The aeroacoustic sources caused by fluctuations in the interactions of the flows leaving the impeller and volute were close to the volute tongue, and the most effective noise sources related to the flow rate were near the impeller shrouds. In addition, the unsteady flow variables provided by CFD calculations were used as inputs in the Ffowcs Williams-Hawkings equation to estimate the noise tones of the fan. The aeroacoustic calculation results showed that the volute noise was much larger than the blade noise, and the noise mainly propagated from the outlet duct of the fan. Moreover, to account for the noise propagation, three calculation methods were used by applying different solid boundaries. Compared with the other methods, the FEM method, which accounted for the complex solid boundaries, produced good agreement and showed that the complex solid boundaries cannot be neglected in aeroacoustic predictions. The calculation results showed good agreement with the experimental results.

Study of flow instability in a centrifugal fan based on energy gradient theory

Flow instability in a centrifugal fan was studied using energy gradient theory. Numerical simulation was performed for the threedimensional turbulent flow field in a centrifugal fan. The flow is governed by the three-dimensional incompressible Navier-Stokes equations coupled with the RNG k-e turbulent model. The finite volume method was used to discretize the governing equations and the Semi-implicit method for pressure linked equation (SIMPLE) algorithm is employed to iterate the system of the equations. The interior flow field in the centrifugal fan and the distribution of the energy gradient function K are obtained at different flow rates. According to the energy gradient method, the area with larger value of K is the place where the flow loses stability easier. The results show that instability is easier to generate in the regions of impeller outlet and volute tongue. The air flow near the hub is more stable than that near the shroud. That is due to the influences of variations of the velocity and the inlet angle along the axial direction. With the decrease of the flow rate, instability zone in a blade channel moves to the impeller inlet from the outlet and the unstable regions in different channels develop in opposite direction to the rotation of impeller.

Investigation of Rotor-Stator Interaction and Flow Unsteadiness in a Low Specific Speed Centrifugal Pump

Instantaneous flow dynamics induced by rotor-stator interaction are detrimental to the stable operation of centrifugal pumps. In this study, unsteady rotor-stator interaction and flow structures within a low specific-speed centrifugal pump are analysed using the Large Eddy Simulation (LES) method. For that purpose, pressure pulsation and the evolution process of a vortical structure are combined to investigate rotor-stator interaction in order to clarify the inherent correlation between pressure amplitude and vorticity distribution. The results show that distinct peaks at blade passing frequency (fBPF) are closely associated with the positions of the monitoring point due to rotor-stator interaction. An unsteady vortical structure at the near tongue region is related to the relative position of the impeller with respect to the tongue, and the upstream effect of the volute tongue significantly affects the vorticity distribution on the blade pressure side. Rotor-stator interaction is dominated by vortex shedding in the wake of the blade trailing edge and their impingement on the volute tongue with subsequent cutting and distortion. Moreover, the high-pressure amplitude is generated with the corresponding high vorticity magnitude observed as well. Therefore, it is confirmed that pressure amplitude is significantly associated with the corresponding vorticity magnitude.

Numerical investigation of influence of the clocking effect on the unsteady pressure fluctuations and radial forces in the centrifugal pump with vaned diffuser

The relative position between the diffuser vane and the volute tongue (clocking effect) has a great effect on the performance of the single-stage centrifugal pump, which however, is often ignored by designers. In this paper, the influence of clocking effect on the unsteady pressure fluctuation in a centrifugal pump and on the radial force of impeller is investigated. The hydrodynamic performance of the centrifugal pump with vaned diffuser was experimentally measured. Numerical simulation based on the Reynolds-averaged Navier–Stokes (RANS) combined with the SST k-w turbulence model was used to obtain hydrodynamic performance of the centrifugal pump. The numerical results of the hydrodynamic performance were in agreement with the experimental data. The results show that the clocking effect has great influence on the pressure fluctuation and on the unsteady radial force imposed on the impeller. When the diffuser vane approaches the volute tongue, the pressure fluctuation intensity in volute is relatively lower. Meanwhile, relatively larger radial force on the impeller and the lower efficiency are obtained when the diffuser vane is near the volute tongue. Thus, it is suggested that the volute tongue should be located near the middle of two diffuser vanes to obtain better performance.

An Investigation of Nonlinear Flow Oscillations in a High-Pressure Centrifugal Pump

High-pressure multistage pumps and their coupled piping systems, typically used in the process and power generation industry, can experience dangerous system-level instabilities. This can occur at flow coefficients well away from the surge limit and in the absence of cavitation. Such a pumping system and a related new kind of instability are the focus of this paper. A system-wide instability was observed at 0.05 times rotor frequency for flow coefficients near maximum head rise but at negative slope, thus on the stable side of the head rise characteristic. A previous study based on system-level experiments concluded that this instability differs from classical surge, cavitation surge, rotating stall, and rotating cavitation, but the underlying mechanism and necessary flow conditions remain unknown. This paper investigates the root cause of the system-wide pump instability, employing a systematic analysis of the impact of geometry changes on pump stability and performance. It is found that the upstream influence of the unsteady flow separation in the return channel leads to a time-varying incidence angle change on the volute tongue which causes periodic ingestion of low-stagnation pressure fluid into the diffuser passages. This sets up a limit cycle, promoting the system-wide instability. With the instability mechanism determined, the pump is redesigned to remove the flow separation while maintaining performance at design conditions. Unsteady numerical simulations demonstrate improved efficiency and pressure recovery at low flow coefficients. A time accurate calculation also indicates stable operation at all relevant flow conditions. The paper resolves a long-standing pump stability problem and provides design guidelines for reliable and improved performance, important to the chemical processing and power generation industry.

Numerical simulation and analysis of solid-liquid two-phase three-dimensional unsteady flow in centrifugal slurry pump

Based on RNG k-e turbulence model and sliding grid technique, solid-liquid two-phase three-dimensional (3-D) unsteady turbulence of full passage in slurry pump was simulated by means of Fluent software. The effects of unsteady flow characteristics on solid-liquid two-phase flow and pump performance were researched under design condition. The results show that clocking effect has a significant influence on the flow in pump, and the fluctuation of flow velocity and pressure is obvious, particularly near the volute tongue, at the position of small sections of volute and within diffuser. Clocking effect has a more influence on liquid-phase than on solid-phase, and the wake-jet structure of relative velocity of solid-phase is less obvious than liquid-phase near the volute tongue and the impeller passage outlet. The fluctuation of relative velocity of solid-phase flow is 7.6% smaller than liquid-phase flow at the impeller outlet on circular path. Head and radial forces of the impeller are 8.1% and 85.7% of fluctuation, respectively. The results provide a theoretical basis for further research for turbulence, improving efficient, reducing the hydraulic losses and wear. Finally, field tests were carried out to verify the operation and wear of slurry pump.

Optimization of Low-Noise and Large Air Volume Blower Based on Load Characteristic

The blower is a kind of garden machinery, which blows strong wind to clean up leaves by a centrifugal fan, but it causes a loud aerodynamic noise. To compromise the contradiction between large air flow rate and low fan noise, some optimizations are proposed to reduce fan noise without lowering its air volume. In this paper, a CFD numerical model to compute airflow field of blower is established, where the centrifugal fan is simulated by the MRF model, and theturbulent model is selected. By smoothing the transition section, improving the volute tongue and optimizing the shape and optimizing number of fan blade, the blower work performance is increased obviously. In order to find out the actual working point, both the fan and motor load characteristic curves are drawn out. The simulation results show that, at the actual working point, the speed of the centrifugal fan is reduced, while the flow rate of blower is raised up. The optimizations are applied to the blower, and the experiment of the improved blower shows the flow rate is increased 5%, and the noise is reduced 2dB.

소형 원심 압축기의 성능 향상을 위한 베인 없는 디퓨저와 볼류트 케이싱의 설계에 관한 연구

Abstract The performance improvement of a small centrifugal compressor for waste water treatment has been conducted by the design change of vaneless diffuser and volute casing. Existing two compressors use a common impeller, but the width and length of the vaneless diffuser and the cross-sectional shape of the volute casing are different, respectively. Based on the experiment of the existing two compressors and their CFD results, the designof the vaneless diffuser and the volute casing has been changed. It was found that the strength of the interaction among the volute tongues, the vaneless diffusers and the impellers of two existing/one improved compressors, was affected by the cross-sectional area and inlet radial length of the volute casing including system losses’ change. Theefficiency of the impeller with one existing design was increased as the decrease of the width of the vaneless diffuser,but losses at the diffuser were accumulated. In conclusion, approximately 2.88%p efficiency increase at the designpoint of the new compressor with the improved design has been confirmed by CFD analysis results.

Experimental and numerical study of external performance and internal flow of a molten salt pump that transports fluids with different viscosities

Molten salt centrifugal pump is used to deliver high temperature molten salt, whose performance is highly affected by the fluid viscosity. In order to investigate the external performance and internal flow of molten salt pump for different viscous fluids, especially reveal the effect of viscosity on unsteady performance, the unsteady flow in a molten salt pump was researched when the pump handles the fluids with different viscosities by numerical simulation to quantitatively clarify the effects in this article. The external performance estimated using the unsteady flow model was compared with experimental results. By taking water as the working fluid, the velocity profiles near the volute tongue were validated by the results of particle image velocimetry (PIV) measurements. It shows that the numerical simulation results agree well with the experimental results. The shaft power increases with the increase of density and viscosity. Compared with delivering water, the head and efficiency show less change for delivering low viscosity fluids (μ<0.044Pa·s), while for delivering high viscosity fluids (μ>0.044Pa·s), they all decrease significantly. Flow steadiness in the molten salt pump is mainly affected by the viscosity and the interference effect of blade. An increasing viscosity of fluid reduces the fluctuation in flow variables. The results of the study have reference significance on the development of high-performance molten salt pump and stable operation.

Numerical and Experimental Study on the Tonal Noise Generation of a Radial Fan

The main focus of this work is on the geometrical modifications can be made to the fan wheel and to the volute tongue of a radial fan to reduce the tonal noise. The experimental measurements are performed by using the in-duct method in accordance with ISO 5136. In addition to the experimental measurements, CFD (computational fluid dynamics) and CAA (computational aeroacoustics) simulations are carried out to investigate the effects of different modifications on noise and performance of the fan. It is shown that by modifying the blade outlet angle, the tonal noise of the fan can be reduced without impairing its aerodynamic performance. Moreover, it is indicated that increasing the number of blades leads to a significant reduction in the tonal noise and also an improvement in the aerodynamic performance. However, this trend is only valid up to a certain number of blades, and a further increment might reduce the aerodynamic performance of the fan. Besides modifying the impeller geometry, new volute tongues are designed and tested on the rig. It is demonstrated that the shape of the volute tongue plays an important role in the tonal noise generation of the fan. Moreover, in order to find out whether or not it is possible to reduce the tonal noise level through a destructive phase-shift generation, stepped tongues are comprehensively investigated by means of numerical simulations and experimental measurements.

Analyses of steady and unsteady flows in a turbocharger’s radial turbine

This study presents the aerodynamic behaviours of a twin-entry radial inflow turbine under steady and transient conditions. The influence of the volute tongue is depicted by a low momentum wake propagating toward the rotor entry, but its effect does not extend beyond a circumferential position of 60°, and more total pressure loss is revealed with respect to the hub side. The transient simulations carried out at different operating conditions and Fast Fourier Transform analysis of static pressure fluctuations induced by the components’ interactions have revealed a space-time periodic behaviour which has been described by a double Fourier decomposition. The flow simulations considering the two sides subject to both non-pulsatile and pulsatile flows conditions have revealed the existing rotor and tongue potential effects and interaction effects the rotor and volute, in addition to the circumferential and spanwise flow non-uniformities at the volute exit, which are more accentuated with a pulsatile flow at inlet. The results of Fast Fourier Transform analysis of temporal pressure fluctuations at the inter-space depict an unsteady behaviour related to the pulsatile frequencies which are characterised by high amplitudes. On the other hand, the spatial pressure fluctuations for the non-pulsatile and pulsatile flows conditions seem to have the same dominant modes since Fast Fourier Transform analysis was carried out at a fixed instant.

Pressure fluctuations around volute tongue of centrifugal pump

Pressure fluctuations around volute tongue of centrifugal pump

Effect of the volute tongue profile on the performance of a low specific speed centrifugal pump

In this study, we investigated the effects of volute tongue geometry variation on the head, efficiency, and radial force of a centrifugal pump. Numerical simulation modeling based on [Formula: see text] turbulence with automatic near wall treatments was used to simulate the turbulent flow. The effect of blade position with respect to the volute tongue on instantaneous pump characteristics was investigated. The parametric studies were done for cutwater gap, tongue shape, and volute tongue angle. Numerical results showed that the large cutwater gap caused lower radial force, especially at high flow rates. Investigations using various volute tongue shapes indicated that the short tongue volute decreased the radial force at design and low flow rates. Considering all aspects, the most satisfactory volute tongue angle was found to be 5° less than the outlet velocity angle of the impeller; yielding about 40% lower radial force than others at the design point.

Simulation of air jets for controlling stall in a centrifugal fan

The main goal of the present work is to analyze the three-dimensional unsteady flow field of a centrifugal fan by solving Navier–Stokes equations, coupled with the throttle condition. The results show that rotating stall occurs in the original fan when the flow rate is 4.30 m3/s, and the stall inception first appears at three impeller passages near the volute tongue and front disc. An active control method is proposed to inhibit the stall inception, which involves blowing air at the inlets of the three impeller passages. This blowing control method cannot inhibit the stall inception when the blowing speed is lower than 50 m/s. The stability margin of the centrifugal fan is extended when the blowing speed is increased from 50 to 110 m/s, while no further effect is obvious with a further increase in the blowing speed. At a blowing speed of 110 m/s, rotating stall occurs again when the fan flow reaches 3.46 m3/s. After the application of the nozzle blowing, the safety margin of the centrifugal fan is extended by 13%, and an obvious stability enhancement effect is achieved. From an engineering standpoint, this new active control method for rotating stall offers a valuable means to ensure the safe operation of a centrifugal fan.

Numerical Analysis on Effects of Inlet Bent Pipe’s Position on a Centrifugal Compressor’s Aerodynamic Noise

The inlet connection of a centrifugal compressor is a bent pipe, and a straight pipe is installed between the bent pipe outlet and impeller inlet. The effect of different lengths of the straight pipe on the aerodynamic noise of a centrifugal compressor is numerically simulated. Theresult show that it’s essential to value the inlet bent pipe’s position in the inlet and outlet aerodynamic design. With the increase of straight pipe’s length, the noise radiated from the inlet decreases. When the length is over the pipe diameter, it has little effect on the outlet noise. The increase of straight pipe’s length also makes the circumferential noise decrease. The noise is distorted at approximately 90 ° in the rotational direction of the volute tongue. The sound power level of the compressor decreases to a constant value with the length over the pipe diameter. In the engineering application on aerodynamic noise, the straight pipe’s length before impeller inlet should be longer than the pipe diameter.

Simulation of Entropy Generation under Stall Conditions in a Centrifugal Fan

Rotating stalls are generally the first instability met in turbomachinery, before surges. This 3D phenomenon is characterized by one or more stalled flow cells which rotate at a fraction of the impeller speed. The goal of the present work is to shed some light on the entropy generation in a centrifugal fan under rotating stall conditions. A numerical simulation of entropy generation is carried out with the ANSYS Fluent software which solves the Navier-Stokes equations and user defined function (UDF). The entropy generation characteristics in the centrifugal fan for five typical conditions are presented and discussed, involving the design condition, conditions on occurrence and development of stall inception, the rotating stall conditions with two throttle coefficients. The results show that the entropy generation increases after the occurrence of stall inception. The high entropy generation areas move along the circumferential and axial directions, and finally merge into one stall cell. The entropy generation rate during circumferential propagation of the stall cell is also discussed, showing that the entropy generation history is similar to sine curves in impeller and volute, and the volute tongue has a great influence on entropy generation in the centrifugal fan.

English

The three-dimensional unsteady flow field in centrifugal pump under different flows was numerically simulated based on the commercial fluent software, using standard k-&epsilon; turbulence model, SIMPLE algorithm and sliding mesh technique. The characteristics of the time domain and frequency domain of the pressure pulsations, as well as fluctuation strength were analyzed. The varying locus of transient radial force vector of the centrifugal pump with time and the varying pattern of transient radial force with time were investigated. The results show that the frequencies of the pressure pulsations are mainly the blade passing frequency at the monitoring points, and the most intense pulsation appears at the volute tongue under the same frequency; the variation cycle of the transient radial force is the same with the passing cycle of the blades, and the direction of the radial force deflects anticlockwise as flow rate increases. At the designed flow rate, the distribution region of the radial force vector is the closest to the origin point and the area of the region is the smallest, with the gentlest fluctuation. &nbsp; Key words: Centrifugal pump, transient radial force, pressure pulsation, numerical simulation.

Numerical and Experimental Study of Unsteady Flow in a Large Centrifugal Pump With Stay Vanes

The unsteady flow inside a large centrifugal pump with stay vanes was analyzed in this study. The static performance and pressure fluctuations in the pump were numerically predicted and were compared with experimental data. Considering the relative positions of the impeller to the volute tongue and stay vanes, the static performance which was obtained using a full unsteady calculation was compared with traditional steady calculation results. A comparison of the results with the experimental data showed that the operation condition farther from the design condition resulted in larger differences between the steady simulation and experimental results, with errors beyond reasonable limits, while the performance curves obtained by the unsteady calculations were closer to the experimental data. A comparison of the pressure fluctuations at four monitoring points with the experimental data showed that the amplitudes at HVS1 and HVS2 are much larger than at HD1 and HD2. The main frequency for these four monitoring points, which agreed well with the experimental data, was the blade passing frequency. The relative obvious errors in pressure fluctuations for HD1and HD2 were due to the inlet flow rate variation of the simulation. Thus, unsteady numerical simulations can be used to predict the pressure fluctuations when designing a pump.

Effects of the Radial Gap Between Impeller Tips and Volute Tongue Influencing the Performance and Pressure Pulsations of Pump as Turbine

The radial gap between the impeller tips and volute tongue is an important factor influencing the overall performance and unsteady pressure fields of the pump as turbine (PAT). In this paper, a numerical investigation of the PAT's steady performance with different radial gaps was first performed. The results show that there is an optimal radial gap for a PAT to achieve its highest efficiency. An analysis of the PAT's unsteady pressure fields indicates that the rotorstator interaction of a rotating impeller and stationery volute would cause high frequency unsteady pulsation within the volute and low frequency unsteady pressure pulsation within the impeller. The high frequency unsteady pressure pulsation would propagate through the PAT's flow channel. Thus, the unsteady pressure field within the impeller is the combined effect of these two kinds of pressure pulsations. The unsteady pressure pulsation within the outlet pipe is mainly caused by the propagation of unsteady pressure formed within the volute. With the increase of the radial gap, the amplitude of high frequency unsteady pressure pulsation within the volute caused by the rotor-stator interaction is decreased, while the amplitude of the low frequency unsteady pressure pulsation caused by the rotor-stator interaction within the impeller remains unchanged.