scholarly journals Numerical and Experimental Investigation of the 4-Quadrant Behavior of Different Mixed Flow Diffuser Pumps

2019 ◽  
Vol 4 (1) ◽  
pp. 3 ◽  
Author(s):  
Stefan Höller ◽  
Helmut Benigni ◽  
Helmut Jaberg
Keyword(s):  
Centrifugal Pump ◽  
Flow Direction ◽  
Operating Conditions ◽  
Operation Condition ◽  
Mixed Flow ◽  
Rotation Direction ◽  
Computational Fluid Dynamics Cfd ◽  
Low Specific Speed ◽  
Abnormal Operating Conditions ◽  
Good Agreement

Besides operating a centrifugal pump under normal conditions there are additional operating conditions possible; for example, a pump operated as turbine. Another example would be a pump trip where there are several abnormal operating conditions possible when the direction of flow and/or the direction of rotation are changing. The machine behavior in every possible operation condition can be represented by the complete pump characteristics, often called the 4-quadrant (4Q) behavior of a centrifugal pump. To gather the 4Q behavior, a test rig allowing the flow direction as well as the rotation direction to be reverted is necessary, with time-consuming measurements at variable positive and negative discharge in both directions of rotation the complete pump characteristics are evaluated. In the present study, an approach to investigate the complete pump characteristics by means of computational fluid dynamics (CFD) calculations is presented. With steady-state calculations and additional transient CFD investigations in the normal operating conditions, the whole pump characteristics were calculated accurately. Two different types of mixed flow diffuser pumps were investigated—one equipped with adjustable impeller blades, the second one with comparable low specific speed. Experimental verifications have shown a remarkably good agreement. Furthermore, an exemplary numerical waterhammer analysis shows the successful application of the presented approach.

Flow Field Instability and Rotordynamic Impedances for an Open Impeller Centrifugal Pump in Transient Four-Quadrant Regimes

2020 ◽  
Author(s):  
Md Shujan Ali ◽  
Farzam Mortazavi ◽  
Alan Palazzolo
Keyword(s):  
Flow Field ◽  
Centrifugal Pump ◽  
Turbulence Model ◽  
Flow Direction ◽  
High Energy ◽  
Operating Conditions ◽  
Mesh Deformation ◽  
Pump Impeller ◽  
Transient Regimes ◽  
Dynamic Forces

Abstract The American Petroleum Institute (API) level 2 rotordynamic stability analysis requires determination of possible destabilization forces on a compressor or pump impeller. Dynamic forces in transient regimes are often excluded although a turbomachine impeller may experience transient operation intentionally or accidentally. The centrifugal pump head, flow direction, rotation and torque can be both positive and negative in transient regimes. For example, in a renewable energy application, pump flow direction and rotation are reversed to generate power from the imposed fluid head. The complete characteristics of a centrifugal pump correspond to all four quadrants (4Q) of operation, to encompass all possible operating conditions. It is required to understand centrifugal pump impeller dynamic forces and rotordynamic responses for all 4Q for design, fault diagnostic, instability analysis, upset conditions (such as water hammer, surge etc.) and for reliable operation of high energy density machines. In the open literature, whirling impeller rotordynamic analyses appears only for normal pump operation. Centrifugal pump dynamic forces, rotordynamic impedances and flow instabilities of an open impeller are reported for 4Q operating regimes in this paper. A transient Computational Fluid Dynamics (CFD)-based model is implemented which is applicable to nonaxisymmetric turbomachinery components, such as with a volute and/or vaned diffuser. Whirling motion of the impeller is modeled by imposing mesh deformation at the impeller walls. A phase modulated multi-frequency mesh deformation method is imposed for better numerical efficiency. Reynolds Averaged Navier-Stokes (RANS) equations with the Shear Stress Transport (SST) turbulence model along with a transitional bypass turbulence model are employed for the CFD solution. The results show the underlying flow field instability and stall cells responsible for the impedance shapes. Furthermore, the model is employed for determining the dependence of the outputs on specific speed to extract rotordynamic forces more efficiently. Impeller dynamic forces are found to scale with the size of the impeller for the same eccentricity ratio and the same flow coefficient. Strength of impeller rotating stalls has dependence on whirl frequency ratio.

scholarly journals Numerical Study on Performance Characteristics of Draft Tube of Mixed Flow Hydraulic Turbine

2012 ◽  
Vol 10 ◽  
pp. 48-52
Author(s):  
Ruchi Khare ◽  
Vishnu Prasad
Keyword(s):  
Coming Out ◽  
Draft Tube ◽  
Numerical Study ◽  
Flow Simulation ◽  
Hydraulic Turbine ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Mixed Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Overall Performance

Draft tube is an important component of the hydraulic reaction turbine and affects the overall performance of turbine to a large extent. The flow inside the draft tube is complex because of the whirling flow coming out of runner and its diffusion along the draft tube. The kinetic energy coming out of runner is recovered in draft tube and part of recovery meets the losses. In the present work, the computational fluid dynamics (CFD) has been used for flow simulation in complete mixed flow Francis turbine for performance analysis for energy recovery, losses and flow pattern in an elbow draft tube used in Francis turbine at different operating conditions. The overall performance of the turbine at some typical operating regimes is validated with the experimental results and found to be in close comparison.DOI: http://dx.doi.org/10.3126/hn.v10i0.7103 Hydro Nepal Vol.10 January 2012 48-52

scholarly journals Numerical analysis for the effect of tip clearance in a low specific speed mixed-flow pump

2019 ◽  
Vol 11 (3) ◽  
pp. 168781401983222 ◽  
Author(s):  
Zhiyi Yu ◽  
Wenwu Zhang ◽  
Baoshan Zhu ◽  
Yongjiang Li
Keyword(s):  
Optimization Design ◽  
Flow Direction ◽  
Tip Clearance ◽  
Mixed Flow ◽  
Ansys Cfx ◽  
Unsteady Simulation ◽  
Low Specific Speed ◽  
Specific Speed ◽  
External Characteristics ◽  
Flow Pump

To study the influence of tip clearance on performance (external characteristics, pressure fluctuation and tip loss) of a low specific speed mixed-flow pump, unsteady simulation was performed for the whole flow passage with five tip clearance sizes ( δ0 = 0 mm, δ1 = 0.10 mm, δ2 = 0.25 mm, δ3 = 0.75 mm and δ4 = 1 mm). The reliability of the numerical methodology was verified in external characteristics (efficiency, head and power) and fluctuation. The performance of the pump was obtained under different discharges and tip clearance sizes using ANSYS CFX. The results showed that the variation of tip clearance size has greater effect on the external characteristics under large discharges. Meanwhile, along the flow direction, the fluctuation coefficients near the impeller shroud increase gradually with the smaller tip clearance sizes ( δ = 0.10 and 0.25 mm), while for the larger tip clearance sizes ( δ = 0.75 and 1.00 mm), the significant increase of fluctuation near the shroud of impeller inlet is closely associated with the clear leakage vortex and the large region of low pressure. Besides, with the increase of tip clearance size, the effect of tip clearance will become more remarkable under different discharge conditions. According to this study, for the optimization design of such pumps, the size of the tip clearance is suggested to be about 0.9% times the blade height at middle of the impeller passage.

An analytical method for determining the optimum number of blades of the compound impeller in a low specific speed centrifugal pump

2020 ◽  
Vol 234 (6) ◽  
pp. 576-587
Author(s):  
Yu-Liang Zhang ◽  
Wen-Guang Li
Keyword(s):  
Centrifugal Pump ◽  
Analytical Method ◽  
Full Length ◽  
Optimum Number ◽  
Centrifugal Pumps ◽  
Design Point ◽  
Closed Type ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Good Agreement

Reasonable methods for determining the optimum number of blades in a low specific speed centrifugal pump with closed-type impeller with splitters, i.e. compound impeller have been rather rare in the literature so far. In the article, a new analytical method was put forward to determine such an optimum number of blades by including the effect of turbulent boundary layer over impeller blades. Three conventional impellers with different numbers of full-length blades and two compound impellers with different numbers of splitters were designed and manufactured. The corresponding performance tests were then conducted. Results showed that the optimum numbers of blades exist for two kinds of impeller in terms of head at design point, pump efficiencies at design point and best efficiency point, and slope of head-flow rate curve at shut-off point. The estimated optimum numbers of blades are in good agreement with the numbers based on the experiments. The conventional impellers with full-length blades are more prone to the hump phenomenon than the compound impellers at the optimum numbers of blades. For the compound impellers, however, the hump effect is negligible at the optimum number of blades, and their head and efficiency are higher than those for the impellers with full-length blades. The method is applicable to compound impeller design in low specific speed centrifugal pumps.

scholarly journals Effects of the outlet position of splitter blade on the flow characteristics in low-specific-speed centrifugal pump

2018 ◽  
Vol 10 (7) ◽  
pp. 168781401878952 ◽  
Author(s):  
Jinfeng Zhang ◽  
Guidong Li ◽  
Jieyun Mao ◽  
Shouqi Yuan ◽  
Yefei Qu ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Suction Side ◽  
Trailing Edge ◽  
Pressure Surface ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Good Agreement

To elucidate the influences of the outlet position of splitter blades on the performance of a low-specific-speed centrifugal pump, two different splitter blade schemes were proposed: one located in the middle of the channel and the other having a deviation angle at the trailing edge of splitter blade toward the suction side of the main blade. Experiments on the model pump with different splitter blade schemes were conducted, and numerical simulations on internal flow characteristics in the impellers were studied by means of the shear stress transport k- ω turbulence model. The results suggest that there is a good agreement between the experimental and numerical results. The splitter blade schemes can effectively optimize the structure of the jet-wake pattern and improve the internal flow states in the impeller channel. In addition, the secondary flow and inlet circulation on the pressure surface of main blade, the flow separation on the suction side of splitter blade, the pressure coefficient distributions on blade surface can achieve an evident amelioration when the trailing edge of splitter blade toward the suction side of the main blade is mounted at an appropriate position.

Development of High-Efficient Centrifugal Pump Through Optimization of Its Volute Tongue and Expeller Vane

2021 ◽  
Author(s):  
Abubaker Ahmed Mohammed Mohammedali ◽  
Ki-Seong Kim
Keyword(s):  
Centrifugal Pump ◽  
Design Parameters ◽  
Outer Diameter ◽  
Hydraulic Efficiency ◽  
Centrifugal Pumps ◽  
Axial Thrust ◽  
High Efficient ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Optimization ◽  
Good Agreement

Abstract Centrifugal pumps are often used for pumping liquids from one priority area to another, which require to work effectively in terms of performance and reliability. The objective of this study is enhancing the hydraulic performance and reliability of a centrifugal pump based on computational fluid dynamics (CFD) optimization. The shapes of expeller vane and volute tongue were optimized based on the following six design parameters; outer diameter, exit angle, front and rear heights, back sidewall gap, and tongue angle. The hydraulic efficiency and axial thrust were chosen as the optimization objectives. In this sense, a design of experiment (DOE) technique was utilized to generate 45 design samples. A response surface modeling (RSM) approach was employed to investigate the interaction between the parameters and objectives. The accuracy of the numerical simulation was verified by the experimental data and showed a good agreement. The optimization was found to improve the hydraulic efficiency by 2.92%, whereas the axial thrust was decreased by 7.51%.

Characterization of Brush Seal Permeability

2016 ◽  
Author(s):  
Thomas G. Gresham ◽  
Brian K. Weaver ◽  
Houston G. Wood ◽  
Alexandrina Untaroiu
Keyword(s):  
Porous Media ◽  
Cfd Simulation ◽  
Flow Direction ◽  
Pressure Ratio ◽  
Operating Conditions ◽  
Backing Plate ◽  
Physical Mechanisms ◽  
Brush Seal ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through

A basis for the study of flow through a brush seal is established by applying the fundamentals of porous media fluid mechanics. Permeability, the measure of a medium’s ability to transmit flow, is one of the most important factors needed to characterize a brush seal’s ability to reduce leakage. Previous studies have indicated that the performance of a brush seal is highly dependent on operating conditions. By investigating how the permeability is affected by the operating conditions (pressure ratio specifically), further understanding of the performance of this type of seal is developed. Experimental data in the literature was used in tandem with computational fluid dynamics (CFD) simulation results in order to characterize how the permeability of a single-stage brush seal changes as the pressure ratio changes. For each value of pressure ratio, the permeability of the CFD model was adjusted until the leakage calculated from the model matched experimentally measured values. The physical mechanisms behind the observed variations in permeability are discussed. Explanations are proposed based on flutter and deformation of the bristles and how these phenomena can affect the internal tortuosity of the bristle pack. As pressure across the bristles increases, it is expected that they will bend under the backing plate to align with the flow direction in the clearance region, but the increase in pressure will also act to compress the bristle pack in the flow direction, decreasing the spacing between bristles and reducing their ability to move relative to each other, thereby reducing the effective permeability of the bristle pack. By demonstrating the dependence of permeability on operating conditions, it is shown that the common assumption of constant permeability coefficients can often result in an insufficient model. Assumptions regarding the model of a bristle pack as an isotropic porous media are discussed, and the validity and utility of this model are assessed. This paper provides important insight into what a reasonable value of permeability of a typical brush seal is, and how that value may change as a function of operating conditions.

Laser Velocimeter Measurements of Axial Velocity Field in the NASA Supersonic Fan Rotor

2001 ◽  
Author(s):  
J. Lepicovsky ◽  
E. P. Braunscheidel ◽  
R. J. Bruckner ◽  
D. L. Tweedt
Keyword(s):  
Experimental Data ◽  
Mach Number ◽  
Axial Velocity ◽  
Operating Conditions ◽  
Laser Doppler Velocimeter ◽  
Computational Data ◽  
Supersonic Regime ◽  
Computational Fluid Dynamics Cfd ◽  
Point Data ◽  
Good Agreement

An analysis of laser Doppler velocimeter (LDV) data for the axial velocity flowfield in the rotor of the Mach 2 inlet flow supersonic throughflow fan (SSTF) is presented in this paper. The paper starts with a short description of the SSTF test package to highlight the specifics of the SSTF operation. It is followed by a detailed description of a dedicated LDV system for measurement in a supersonic throughflow fan and the experience gained. Most of the experimental data presented were acquired in a low supersonic throughflow regime (inlet Mach number of 1.4). The results and conclusions presented are based mainly on the experimental data only. A limited amount of computational fluid dynamics (CFD) predictions were used for comparison with the experimental results. The CFD methods, however, are not discussed in this paper. As shown in this paper, a reasonably good agreement between the LDV data and the CFD predictions was found for the low supersonic throughflow regime. The design point data (inlet Mach number of 2.0) exhibited an unexpectedly high noise in the velocity data in comparison with the data for low supersonic throughflow operating conditions. For the off-design supersonic regime (shock in rotor), substantial differences exist between the experimental and computational data.

Numerical Investigation of Pressure Pulsation in Vaneless Region of a High Speed Centrifugal Pump

2019 ◽  
Author(s):  
Yongshun Zeng ◽  
Min Yang ◽  
Yuqing Zhai ◽  
Zhifeng Yao ◽  
Fujun Wang ◽  
...  
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Pressure Pulsation ◽  
Simulation Method ◽  
Operating Conditions ◽  
Pressure Pulsations ◽  
Flow Rates ◽  
Rotor Stator Interaction ◽  
Frequency Components ◽  
Good Agreement

Abstract The pressure pulsation due to rotor-stator interaction (RSI) is unavoidable for high-speed centrifugal pump when operating under different conditions. The frequency components of pressure pulsation in the vaneless region are the most complex, and the pressure pulsation characteristic plays an important role in pump structural stress analysis. A numerical simulation method is used to obtain the hydraulic performances of a high-speed centrifugal pump with 9857 r/min at the range of flow rates between 48.1 to 155.0 m3/h. The head and efficiency under different operating conditions have good agreement with experimental results, with maximum deviations in 3.82% and 5.37%, respectively. The results show that the level of the pressure pulsation from the inlet to the outlet of the impeller increased gradually, and the pressure pulsations between the short blades are greater than that between the long and short blades. In the diffuser, the pressure pulsation is the highest near the tongue, whereas it is lower in the region between the two tongues, and this region is defined as the vaneless region. The pressure contours in the vaneless region almost have no change, while they near the tongue are densely distributed, revealing the mechanism of uneven pressure pulsation distribution. Moreover, there is a high radial velocity distribution near the tongue in the vaneless region, indicating that there may be a jet-wake pattern occured in this region.

Numerical Research of Film Boiling Heat Transfer Around a Vertical Short Cylinder With Flat or Hemispherical Ends

2016 ◽  
Vol 138 (7) ◽  
Author(s):  
Rubén Arévalo ◽  
Alberto Abánades ◽  
Luis Rebollo
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Vertical Cylinder ◽  
Operating Conditions ◽  
Film Boiling ◽  
Loss Of Coolant Accident ◽  
Computational Fluid Dynamics Cfd ◽  
Experimental Values ◽  
The Individual ◽  
Abnormal Operating Conditions

Film boiling is a heat transfer mechanism that might appear in different processes, such as cryogenics, metallurgical, and nuclear reactors during abnormal operating conditions, as happens during a loss of coolant accident. In this research, film boiling around a finite vertical cylinder was studied by means of computational fluid dynamics (CFD) simulations, considering six cases that include three different levels of surface temperature and two different shapes of the cylinder ends: flat and hemispherical ends. Volume of fluid (VOF) method for the treatment of multiphase flow was used, and a user-defined function was programed to consider the exchange of mass and energy between the phases. The simulations were performed with a vertical cylinder of 32 mm in diameter and 32 or 64 mm in high for flat ends or hemispherical ends, respectively, placed in a two-dimensional axisymmetric domain of 0.125 m × 0.25 m. Results obtained for the heat flux show a periodic fluctuating behavior in time as a consequence of periodical variations in the thickness of the vapor film around the cylinder. A wavy liquid–vapor interface is observed as is reported in the experimental works. The simulations results are compared with the experimental values reported in literature as well as with values obtained from correlations. The results show that the computational code used captures reasonably well the physics involved in the film boiling, being obtained that average heat flux to the case of hemispherical ends is 15.6% higher than for the case of flat ends, versus 15.2% showing experiments and 1.6% calculated combining correlations for the individual surfaces. It shows that use of correlations in this way is not appropriate in film boiling because it does not take into account the interactions between the different surfaces.

Sign in / Sign up

Export Citation Format

Share Document