Impeller Area Research Articles

The influence of ring clearance on the performance of a double-suction centrifugal pump

Due to the complex structure of a double-suction pump's suction chamber, the flow in the pump's cavity is often ignored in numerical simulations because of difficulties in structured hexahedral meshing. However, the wear ring clearance interlinking the pump chamber leads the fluid at the impeller inlet directly to the impeller area. This significantly impacts the pump's internal flow field, so the influence of the clearance on the internal flow of a double-suction pump cannot be ignored. This paper develops four three-dimensional double-suction pump models with different wear ring clearances to investigate their influence on pump performance, and structured hexahedral meshes were used for all the computational domains. The clearances varied from 0.2 to 0.5 mm in 0.1 mm increments. The influences of the clearance on the energy loss, external characteristics, and internal flow field distribution of the pump were simulated via a verified computational fluid dynamics method. The results show that the wear ring leakage decreases with the flow rate and increases with wear ring clearance. The increase in backflow leads to an internal flow disorder inside the impeller, resulting in a decreased head and efficiency. Energy loss is mainly caused by increasing the turbulence entropy production with an increasing wear ring clearance. Also, the low-pressure region in the pump cavity expands to the volute with increasing clearance, and the impeller outlet pressure decreases. This study's research on wear ring clearance provides a reference for the design and application of double-suction centrifugal pumps.

Mixing tank hydrodynamics and mixing efficiency for propeller impellers

In this study, the distribution of axial and radial velocities with the use of a PIV laser system was determined and the mixing power in a mixing tank with narrow and wide propeller impellers was measured. The pumping capacity and secondary circulation values in the mixing tank were calculated and on this basis, the energy efficiency of the operation of both types of propeller impellers was determined and compared with the efficiency of turbine impellers with inclined blades. It turned out that propeller impellers with wide blades are most effective as regards the amount of energy that should be supplied to the mixing tank to achieve the required mixing time. It was found that the share of pumping capacity in the total secondary circulation is almost twice as high as the share of induced circulation. Correlation equations for the dependence of the mixing power and dimensionless flow numbers on the pitch of the propeller blade were also formulated. All the results obtained were compared with the works of other authors. The paper also found that propeller impellers with a variable angle of inclination of the blade α depending on the current radius do not meet the theoretical assumption of a constant axial velocity of the liquid flowing out from of the impeller zone. For small radii of the impeller the explanation for this observation is the presence of the hub and shaft in the axis of the mixer and the effect of liquid slip for the steep agitator blades near the hub. For radii close to the radius of the stirrer, the reason is generation of induced circulation as the expense of the kinetic energy of the liquid flowing out of the impeller area.

Numerical study on the performance of centrifugal blood pump with superhydrophobic surface.

In order to reduce the blood damage of an artificial heart pump and optimize its hydraulic performance, a centrifugal blood pump with superhydrophobic characteristics is proposed in this study. To study the influence of superhydrophobic surface characteristics on the performance of centrifugal blood pumps, the Navier slip model is used to simulate the slip characteristics of superhydrophobic surfaces, which is realized by the user defined function of ANSYS fluent. The user defined functions with different values of slip length are verified by two benchmark solutions of laminar flow and turbulence in the pipeline. The blood pump model adopts the designed centrifugal blood pump, and its head, hydraulic efficiency and hemolysis index are calculated. The Navier slip boundary condition (a constant slip-length of 50 μm) is applied to the walls of the blood pump impeller and a volute at different positions, and the influence of the superhydrophobic surface on the performance of the blood pump at the design point Q = 6 L/min was compared and analyzed. The results show that the centrifugal blood pump model used in this paper has good blood compatibility and meets the design requirements; the superhydrophobic surface can significantly reduce the scalar shear stress in the blood pump. At the design point, when the slip length is 50 μm, the mass-average scalar shear stress in the impeller area and the volute area reduction rate is about 5.9%, the hydraulic efficiency growth rate is about 3.8%, the hemolysis index reduction rate is about 18.4%, and the pressure head changes little with a growth rate of 0.3%. Centrifugal blood pumps with superhydrophobic surfaces can improve the efficiency of blood pumps and reduce hemolysis. Based on these encouraging results, vitro investigations for actual blood damage would be practicable.

Numerical Calculation of Solid-Liquid Two-Phase Flow in Open-Design Vortex Pump

This paper mainly based on the CFD platform, numerical simulation of the internal flow field in the open-design vortex pump under different solid particle concentration and particle size is carried out to explore the flow trajectory characteristics of solid particles in the impeller channel and the lateral cavity, as well as the distribution characteristics of solid particles, and calculate the sliding velocity of particles in the impeller channel. The results show that at different solid particle concentrations, the solid volume fraction f in the front and rear cover plate area of the blade is high and that in the middle area is low; The solid volume fraction f decreases gradually from the working face to the back, and the solid particles are widely distributed in the inlet area. Due to the asymmetry of the volute structure, the particle concentration in the inlet area corresponding to the casing tongue is significantly higher than that in other areas; Due to the existence of circulating flow and through flow, the solid particles are distributed in a circular direction in the lateral cavity, and the particle concentration in the middle region is large; In the impeller area corresponding to the casing tongue, the sliding velocity of solid particles decreases with the increase of particle size, and the sliding velocity values of 0.5mm and 1.0mm particle sizes are close.

Investigation of the hydrodynamic characteristics of an axial flow pump system under special utilization conditions

In actual operation, axial flow pump stations are often used for various special purposes to meet changing needs. However, because the hydrodynamic characteristics of axial flow pump systems are still unclear when used for special purposes, there are many risks when pump systems are used for special purposes. To explore the hydrodynamic characteristics of an axial flow pump system under special utilization conditions, a high-precision full-feature test bench for an axial flow pump system is established in this paper. For the first time, an energy characteristics experiment and a pressure fluctuation measurement for a pump are carried out for a large axial flow pump system model under zero head, reverse pump and reverse power generation conditions. Then, ANSYS CFX software is used to solve the continuous equation and Reynolds average Navier–Stokes equation, combined with the SST k–ω turbulence model, and the characteristic curve and internal flow field of the pump system under special conditions are obtained. Finally, the numerical simulation results are compared with the experimental results. The results show that the velocity gradient distribution in the pump is uniform under the near zero head condition (NZHC), and there is no obvious flow collision and reflux phenomenon in the pump. Compared with the designed condition (DC), the peak-to-peak value (PPV) of pressure pulsation at the inlet of the impeller decreased by 67.16%, and the PPV at the outlet of the impeller decreased by 8.14% at H = 0 m. The maximum value of the main frequency amplitude (MFA) in the impeller area appears at the impeller inlet. Under reverse pump conditions (RPC), the phenomenon of unstable flow in the pump system is obvious, and a large range of recirculation zones appears in the nonworking face of the blade. Compared with the DC, the PPV of the impeller inlet at the optimal point of RPC increased by 122.61%, and the impeller outlet PPV increased by 11.37%. The maximum value of MFA in the impeller area appears at the impeller inlet. Under the reverse power generation condition (RPGC), no obvious flow separation was found in the nonworking face of the impeller. Compared to the DC, the PPV of the impeller inlet at the optimal point of the RPGC increased by 65.34%, and the PPV of the impeller outlet increased by 206.40%.

Analysis of the Formation Mechanism and Evolution of the Perpendicular Cavitation Vortex of Tip Leakage Flow in an Axial-Flow Pump for Off-Design Conditions

To understand the formation mechanism and evolution process of the perpendicular cavitation vortex (PCV) of an axial flow pump for off-design conditions, turbulent cavitating flows were numerically investigated using the rotation curvature-corrected shear stress transport (SST-CC) turbulence model and the Zwart–Gerber–Belamri cavitation model. In this work, the origin and evolution of a PCV were analyzed through a high-speed photography experiment and numerical simulation. The results showed that the PCV came from a secondary tip leakage vortex (S-TLV) and was aggregated by the action of the re-entrant jet, combined with the cavitation bubbles driven by the radial flow to form the cavitation vortex (CV). With the joint action of leakage jet lifting and TLV entrainment, the PCV was reoriented and gradually became perpendicular to the chord direction. Then, the PCV and TLV collided, mixed, and entrained, which formed a strong pressure pulsation. The PCV was gradually divided into upper and lower parts. One part was combined with the residual part of the TLV and flowed to the next blade, and the other part flowed out of the impeller area along the axial direction. At the same time, the generation, evolution, and dissipation of the PCV formed high pulsation amplitudes and frequencies in the middle and rear above the blade suction.

Numerical analysis of the effects of gas-phase properties on the internal characteristics and wear in a centrifugal pump

Centrifugal pumps are indispensable in aquaculture engineering. The existence of bubbles is inevitable in a centrifugal pump and may affect the performance of the pump which delivers solid-liquid two-phase flow. Thus, this study aims to analyze the effects of gas-phase properties on the internal characteristics of a centrifugal pump by using a computational fluid dynamic code based on Eulerian multiphase mode and a standard k–ε two-equation turbulence model. Results show that gas-phase properties, such as concentration and diameter, affect the absolute pressure and the phase distribution in the centrifugal pump. The gas-phase distribution on the working faces of blades is greater than forces on the back face of the blades. The larger the diameter of the gas-phase is, the easier it is to be concentrated; Thus, the working face of the blades is prone to cavitation and corrosion, and with the increase of the bubble size, the cavitation corrosion of the back surface of the impeller becomes more serious. The solid-phase velocity and static pressure distribution increase with increasing concentration or diameter of gas-phase. The solid-phase is more easily leave the impeller area and enter the volute because of the existence of gas-phase, which may lead to abrasion of volute. The existence of gas makes the solid velocity distribution in the centrifugal pump more uneven, which may cause uneven wear of the centrifugal pump. The obtained results by this method can reveal the effects of gas-phase properties and wear on the internal characteristics in centrifugal pumps and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.

PIV experimental study on flow structure and dynamics of square stirred tank using modal decomposition

Stirred mixing is one of the important unit operations in the chemical, petroleum, pharmaceutical and food industries. The mixing of liquids is achieved by a rotating shear flow field formed by a periodic jet flow from the impeller. In this work, we investigated the flow structure in a square stirred tank without baffles and with a Rushton impeller (RT) using particle image velocimetry (PIV) technique. The instantaneous flow fields were obtained as a function of various rotations per minute (rpm) for the impeller (N=120, 150, 180, 210 and 240 rpm), while phase-resolved velocity information was obtained for N=150 rpm. The proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) methods were applied to analyze the velocity fields, flow structure and dynamic information in the absence of impeller area. As demonstrated by the results, there is a wide range of spatial and temporal scales throughout the process. The high energy parts exist in two kinds of structures except for the average fluid flow. The instability phenomenon results from the cyclic shear flow and the trailing vortices structure caused by the periodic jet near the blade passage frequency. As the Reynolds number is on the rise, the periodic flow increases, the random turbulence is reduced, and the flow tends to the ultimate stable state. The square section acts like baffles to change the direction of the fluid circumferential velocity while increasing the radial and tangential flow, which is conducive to mixing. This study provides a basis for understanding the flow structure and unsteady characteristics in a square stirred mixing tank.

Numerical Investigation of Flow Field Behaviour and Pressure Fluctuations within an Axial Flow Pump under Transient Flow Pattern Based on CFD Analysis Method

In this present work, CFD numerical method is applied to analyses the flow field in an axial flow pump qualitative and quantitative analyses. Qualitative analysis for these parameters comprise static pressure variations, dynamic pressure variations, velocity magnitude, turbulent kinetic energy, shear stress. Quantitative analysis including the pressure fluctuations in frequency domain analysis under different operation conditions. Also, sliding mesh method and turbulence model type k-epsilon are used. Various monitoring points are stalled in order to analyses pressure fluctuation mechanism in the impeller blade. The numerical results revealed that the flow field for pressure and velocity are increase start from the suction side of the pump to discharge side. Also, the results found that the high pressure occurs at the discharge side along the axial direction of the impeller. The maximum value of pressure fluctuations is occurred at tip blade region due to high interaction flow at this particular area. Moreover, the pressure decreases as flow rate in the pump increases. Additionally, the results shown that the pressure fluctuations have four peaks and four valleys the similar impeller blades number. Furthermore, there are different positive and negative pressure regions, the negative pressure area occurs due to lower pressure zone at inlet impeller area and hence which can lead to cause occurrence of cavitation in this specific area. The current numerical demonstration results can help the researches for further axial flow pump design.

PIV experimental study on the flow field characteristics of axial flow blood pump under three operating conditions

In order to investigate the internal flow field of an axial blood pump, two-dimensional (2D) particle image velocimetry (PIV) was applied to test the blood pump under three different conditions. Acquiring the images of inlet, front guide vane, impeller, back guide vane and outlet area, the distribution of internal flow field was then analysed. The rotation speed of the blood pump was set to 6000, 7000 and 8000 r/min, respectively. The results show that the flow field of blood pump is stable relatively at the inlet area. Some vortices and reflux existed due to the block of guide vane in the import and impeller area. With the increase of rotating speed, the overall disturbance degree of flow field increases. Under the condition of low rotation speed, the flow field acceleration is insufficient. Under the medium rotation speed condition, the flow field is stable and the velocity distribution is even. Under the condition of high rotating speed, the number of vortices in the flow field increased significantly, the flow separation phenomenon at the impeller was obvious and more unstable flow appeared at the back guide vanes and outlet area.

PIV Experimental Study of the Axial Flow Blood Pump’s Internal Flow Field Under Pulsatile Condition

Taking the axial flow blood pump as the research object, we used the particle image velocimetry (PIV) to measure the flow distribution of inlet, outlet and impeller at the changing rotation speed. Effects of the acceleration and deceleration process on the change of internal flow field were compared and analyzed. The experimental results show that the flow field of inlet and outlet area of the blood pump is stable at the constant working speed, but the vortex and reflux exist in the impeller area. However, acceleration of the impeller increases the flow field’s volocity and disturbance. Deceleration of the impeller rotation speed reduces the flow velocity, and the flow state of overall flow field is relatively stable. Design of the pulsatile blood pump should be optimized in order to reduce the occurrence of hemolysis in the process of acceleration and deceleration.

Effect of Impeller Condition on Blower Performance, Case Study: Impeller of K-2201 in Pt. Pertamina RU III

The performance of blower depends on impeller condition. This paper is to discuss the open face impeller condition related to performance based on performance curve provided by the manufacturer. The impeller condition is observed under three different conditions. The first condition is that the impeller area is covered by 3 mm thick of fouling. The second condition is that there is a 1 mm of rubbing on the vane and the third condition is the impeller after being repaired. The datas are taken by the actual operation condition. The observed data is then calculated and plotted on OEM performance curve. The result shows that the first condition has the lowest performance; the produced head is 47% lower than the OEM’s.

Lumped Capacitance and Three-Dimensional Computational Fluid Dynamics Conjugate Heat Transfer Modeling of an Automotive Turbocharger

One-dimensional wave-action engine models have become an essential tool within engine development including stages of component selection, understanding system interactions, and control strategy development. Simple turbocharger models are seen as a weak link in the accuracy of these simulation tools, and advanced models have been proposed to account for phenomena including heat transfer. In order to run within a full engine code, these models are necessarily simple in structure yet are required to describe a highly complex 3D problem. This paper aims to assess the validity of one of the key assumptions in simple heat transfer models, namely, that the heat transfer between the compressor casing and intake air occurs only after the compression process. Initially, a sensitivity study was conducted on a simple lumped capacity thermal model of a turbocharger. A new partition parameter was introduced αA, which divides the internal wetted area of the compressor housing into pre- and postcompression. The sensitivity of heat fluxes to αA was quantified with respect to the sensitivity to turbine inlet temperature (TIT). At low speeds, the TIT was the dominant effect on compressor efficiency, whereas at high speed αA had a similar influence to TIT. However, modeling of the conduction within the compressor housing using an additional thermal resistance caused changes in heat flows of less than 10%. Three-dimensional computational fluid dynamics (CFD) analysis was undertaken using a number of cases approximating different values of αA. It was seen that when considering a case similar to αA = 0, meaning that heat transfer on the compressor side is considered to occur only after the compression process, significant temperature could build up in the impeller area of the compressor housing, indicating the importance of the precompression heat path. The 3D simulation was used to estimate a realistic value for αA which was suggested to be between 0.15 and 0.3. Using a value of this magnitude in the lumped capacitance model showed that at low speed there would be less than 1% point effect on apparent efficiency which would be negligible compared to the 8% point seen as a result of TIT. In contrast, at high speeds, the impact of αA was similar to that of TIT, both leading to approximately 1% point apparent efficiency error.

Noise reduction of dry vacuum pump using the boundary element method to model impeller blade passage frequency

Acoustic field analysis was conducted to propose noise reduction measures for the suction housing of a vacuum pump used in dentistry. The target frequency for reduction was selected by measuring the sound pressure level during steady-state operation, allowing identification of the primary noise sources through intensity and vibration measurements. The impeller area was analyzed by designing a full-scale analytic model for sound field analysis using reverse engineering, including precise 3D modeling. The inner boundaries were then separately extracted to complete a model for acoustic analysis. The characteristics of the inner suction housing area were analyzed using the Boundary Element Method (BEM). Noise reduction measures were proposed by analyzing the characteristics of the suction housing with respect to the differences in excitation frequency brought about by changing the number of impeller blades used. The acoustic frequency response function (FRF) of the inner suction housing was obtained by applying BEM. The relationships between the suction housing and the noise source were investigated to propose noise reduction measures. The proposed measure of reducing impeller blade number was validated by showing that it would avoid resonance in the suction housing by moving the BPF to a lower frequency. Thus, this study proposed the reduction of the number of impeller blades to reduce the noise of the current suction housing design considerably while maintaining its performance.

Experimental and numerical analysis on noise reduction in a multi-blade centrifugal fan

In this work, analysis on noise source and reduction in a multi-blade centrifugal fan used for air-conditioners was carried out by experimental and numerical methods. Firstly, an experimental system using microphone mounted on volute surface for measuring surface pressure fluctuations of volute was designed and introduced, then surface pressure fluctuations of the whole volute for a multi-blade centrifugal fan were measured by this system, and the inlet noise for this fan was also obtained. And then, based on the experimental results, the aerodynamic noise source of the studied fan was analysed. The surface pressure fluctuations of the volute showed that there were largest surface pressure fluctuations near the volute tongue, and peaks appeared at the Blade Passing Frequency (BPF). The spectra of fan inlet noise showed that the peaks also appeared at BPF, and noise levels in a wide range of frequency were also larger. Secondly, the internal flow of the fan was simulated by commercial software under the same conditions with the experiment, and then the fluid flow and acoustic power field were obtained and discussed. The contours of acoustic power level showed that the larger noise was generated at the impeller area close to the outlet of scroll and at the volute tongue, which is same as that from experiment. Based on all of the results, we can find that the vortex noise is an important part of fan noise for the studied fan, and the rotation noise also cannot be neglected. Finally, several reduction methods that are thought to be effective based on experimental and numerical results were suggested.

Large eddy simulations of the turbulent flow in a stirred reactor

Large eddy simulations of a baffled reactor stirred with a single Rushton turbine were performed. The turbine was positioned at mid-height in the reactor. The unsteady spatially filtered incompressible Navier–Stokes equations have been solved numerically. These large eddy simulations (LES) provide details of the flow field that cannot be obtained with the so-called Reynolds averaged equations and corresponding models. The un-resolved scales have been modelled implicitly through the truncation errors of the discretisation. The motion of the blades was described as time-dependent momentum sources. The time-averaged flow properties, mean flow and turbulence, have been studied. Phase averaging was used to characterize the flow relative to the impeller blades. Power spectral density and correlations, both in time and space were investigated. The results have been compared with the experimental data from several sources and also with the data from other simulations. Comparing our data with measurements we see an overall good agreement both qualitatively and quantitatively. In the impeller stream we observe an acceleration of the flow in the radial direction due to the trailing vortex pair. This acceleration can also be deduced from published experimental and numerical data. There are however some discrepancies concerning velocity fluctuations in the impeller area. These discrepancies are probably caused by inaccuracy in the impeller description.

Substrate gradients in bioreactors: origin and consequences

Gradients of glucose in time and space are shown in a 30 m3 cultivation of Saccharomyces cerevisiae grown in minimal medium to a cell density of 20 gl−1. The fed-batch concept was used with glucose as the limiting component which was fed continuously to the process. As the mean glucose concentration declined throughout the process, the level of glucose was at all times different in three sampling ports (bottom/middle/top) of the reactor. These gradients were furthermore shown to depend on the feed position. This means that if the feed was supplied in the relatively stagnant mixing zone above the top impeller, the gradients were more pronounced than by feed in the well mixed bottom impeller zone. A rapid sampling system was constructed, and continuous glucose samples of every 0.15 s were analysed from a point of the reactor. Fifty samples were collected with this system, but the amount and frequency is possible to change. The results of these series show a variance of the glucose concentration where at one stage, a peak appeared of a relative difference in concentration of 40 mgl−1. The pattern of these rapid glucose fluctuations was shown to depend on the turbulence level at the location of the feed. It was shown, that the fluctuations were more pronounced when the feed was localised in a relatively stagnant area than in the well-mixed impeller area, where the deviation from the mean was negligible. The fluid flow, in the impeller (gassed and ungassed) and bulk area (ungassed) of the reactor, was characterised by turbulence measurements using thermal anemometry. These types of areas resembles well the different areas of sampling as mentioned above. The turbulent frequencies in these areas were in the range of 10−1 to 104 Hz with the highest amplitudes at low frequencies. The spectra depicts a uniform time scale for all zones, especially at the low frequencies. The dominance of low frequency, high amplitude flow variations and the observed short-time oscillations in substrate concentration support the hypothesis of substrate transport over fairly long distances without substantial mixing both in the impeller, but especially, in the bulk zone of the reactor.

Effect of Area Ratio on the Performance of a 5.5:1 Pressure Ratio Centrifugal Impeller

A centrifugal impeller which was initially designed for a pressure ratio of approximately 5.5 and a mass flow rate of 0.959 kg/s was tested with a vaneless diffuser for a range of design point impeller area ratios from 2.322 to 2.945. The impeller area ratio was changed by successively cutting back the impeller exit axial width from an initial value of 7.57 mm to a final value of 5.97 mm. In all, four separate area ratios were tested. For each area ratio a series of impeller exit axial clearances was also tested. Test results are based on impeller exit surveys of total pressure, total temperature, and flow angle at a radius 1.115 times the impeller exit radius. Results of the tests at design speed, peak efficiency, and an exit tip clearance of 8 percent of exit blade height show that the impeller equivalent pressure recovery coefficient peaked at a design point area ratio of approximately 2.748 while the impeller aerodynamic efficiency peaked at a lower value of area ratio of approximately 2.55. The variation of impeller efficiency with clearance showed expected trends with a loss of approximately 0.4 points in impeller efficiency for each percent increase in exit axial tip clearance for all impellers tested. The data also indicated that the impeller would probably separate at design area ratios greater than 2.748. An analysis was performed with a quasi-three-dimensional inviscid computer code which confirmed that a minimum velocity ratio was attained near this area ratio thus indicating separation. These data can be used to verify impeller flow models which attempt to account for very high diffusion and possible separation.