A Study on Impeller-Diffuser Interaction: Part II — Detailed Flow Analysis

2002 ◽  
Author(s):  
Kai U. Ziegler ◽  
Heinz E. Gallus ◽  
Reinhard Niehuis
Keyword(s):  
Strong Influence ◽  
Flow Analysis ◽  
Pressure Side ◽  
Wake Region ◽  
Vaned Diffuser ◽  
Flow Configuration ◽  
Noticeable Reduction ◽  
Radial Gap ◽  
Vane Angle ◽  
Highly Loaded

The interaction between impeller and diffuser is considered to have strong influence on the flow in highly loaded centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time averaged flow configuration in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated stage allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. In part I it was shown that smaller radial gaps improve diffuser pressure recovery, whereas impeller efficiency is hardly affected. Part II focuses on the reasons for these effects. Measurements with a laser-2-focus velocimeter in the highly unsteady flow field between the impeller exit region and diffuser throat were performed at three different diffuser geometries allowing a detailed flow analysis. Especially the unsteady results show that for a smaller radial gap more impeller wake fluid is conveyed towards the highly loaded diffuser vane pressure side reducing its loading and leading to a better diffusion in the diffuser channel. Concerning the impeller flow, it was found that a smaller radial gap is leading to a noticeable reduction of the wake region at impeller exit. The experimental results are intended to be published as an open CFD testcase under the name “Radiver”.

A Study on Impeller-Diffuser Interaction—Part II: Detailed Flow Analysis

2003 ◽  
Vol 125 (1) ◽  
pp. 183-192 ◽  
Author(s):  
Kai U. Ziegler ◽  
Heinz E. Gallus ◽  
Reinhard Niehuis
Keyword(s):  
Flow Field ◽  
Strong Influence ◽  
Flow Analysis ◽  
Test Case ◽  
Wake Region ◽  
Vaned Diffuser ◽  
Noticeable Reduction ◽  
Radial Gap ◽  
Vane Angle ◽  
Highly Loaded

The interaction between impeller and diffuser is considered to have strong influence on the flow in centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time-averaged flow field in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated compressor allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. In Part I it was shown that smaller radial gaps improve diffuser pressure recovery, whereas impeller efficiency is hardly affected. Part II focuses on the reasons for these effects. Measurements with a laser-2-focus velocimeter in the highly unsteady flow field between the impeller exit region and diffuser throat were performed at three different diffuser geometries allowing a detailed flow analysis. Especially the unsteady results show that for a smaller radial gap more impeller wake fluid is conveyed towards the highly loaded diffuser vane pressure side reducing its loading and leading to a better diffusion in the diffuser channel. Concerning the impeller flow, it was found that a smaller radial gap is leading to a noticeable reduction of the wake region at impeller exit. The experimental results are intended to be published as an open CFD test case under the name “Radiver.”

A Study on Impeller-Diffuser Interaction: Part I — Influence on the Performance

2002 ◽  
Author(s):  
Kai U. Ziegler ◽  
Heinz E. Gallus ◽  
Reinhard Niehuis
Keyword(s):  
Strong Influence ◽  
Vaned Diffuser ◽  
Flow Losses ◽  
Extensive Test ◽  
Radial Gap ◽  
Operating Points ◽  
Vane Angle ◽  
Compressor Efficiency ◽  
Probe Measurements ◽  
Highly Loaded

The interaction between impeller and diffuser is considered to have strong influence on the flow in highly loaded centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time averaged flow configuration in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated stage allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. Part I deals with the integral flow losses and the diffusion in impeller, diffuser and the entire compressor. An extensive test series with steady probe measurements at impeller exit and diffuser exit was performed at 10 different diffuser geometries and different operating points. The results show that in most cases smaller radial gaps are leading to a more homogeneous flow field at diffuser vane exit and to a higher diffuser pressure recovery resulting in a higher compressor efficiency. On the other hand, impeller efficiency is hardly affected by the radial gap. In part II measurements with a laser-2-focus velocimeter are presented illuminating the reasons for the effects found. The experimental results are intended to be published as an open CFD testcase under the name “Radiver”.

Boundary Layer and Loss Analysis in a Film Cooled Vane

2001 ◽  
Author(s):  
Giovanna Barigozzi ◽  
Giuseppe Benzoni ◽  
Antonio Perdichizzi
Keyword(s):  
Boundary Layer ◽  
Flow Analysis ◽  
Suction Side ◽  
Wake Flow ◽  
Generation Process ◽  
Pressure Side ◽  
Wake Region ◽  
Trailing Edge ◽  
Loss Analysis ◽  
Coolant Injection

The paper reports on boundary layer and wake flow analysis in a fully covered, film cooled vane without trailing edge ejection. The investigation, carried out in a low speed wind tunnel for linear cascades, has been mainly focused on the loss generation process due to coolant injection. The investigated region includes the rear part of pressure and suction side boundary layers and the wake region, up to a chord length downstream of the trailing edge. All measurements have been performed at mid-span, air being used as coolant flow. The same measurements have been also performed on a solid blade cascade, i.e. without cooling holes. Boundary layer profiles, integral parameters together with mean and turbulent quantities are presented. It results that the showerhead promotes transition on the suction side, giving rise to a thicker boundary layer all over the surface. On the pressure side, the boundary layer remains laminar up to the trailing edge, as high acceleration prevents transition. The wake region seems not to be strongly altered by the coolant injection. Boundary layer profiles and downstream 5-hole probe traverses have been used to compute loss coefficient distributions all over the blade surface and in the downstream region. Coolant injection strongly increases the profile losses along the suction side, while a much smaller contribution from the pressure side has been found. These increases are mainly due to coolant injection in the vane front part.

Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry: Part II—Detailed Flow Analysis

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Stefan Ubben ◽  
Reinhard Niehuis
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Flow Analysis ◽  
Industrial Applications ◽  
Experimental Investigations ◽  
Stall Margin ◽  
Diffuser Flow ◽  
Radial Gap ◽  
The Impact ◽  
Vane Angle

Adjustable diffuser vanes offer an attractive design option for centrifugal compressors applied in industrial applications. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall is still not satisfying. This two-part paper summarizes results of experimental investigations performed with an industrial-like centrifugal compressor. Particular attention was directed toward the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser, and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed. In Part I it was shown that an one-sided diffuser clearance is able to contribute to an increase in flow range, stall margin, pressure ratio, and efficiency. In order to reveal the relevant flow phenomena, in Part II the results of detailed measurements of the pressure distribution at diffuser exit and particle image velocimetry (PIV) measurements inside the diffuser channel performed at three clearance configurations and three diffuser angles at a fixed radial gap are discussed. It was found that, for defined diffuser configurations, the clearance flow amplifies the diffuser throat vortex capable to reduce the loading of the highly loaded vane pressure side and to support a more homogenous diffuser flow. It turned out that the co-action of the geometry parameter diffuser vane angle and diffuser clearance height is of particular importance. The experimental results are published as an open computational fluid dynamics (CFD) testcase “Radiver 2.”

Flow Analysis in a Pump Diffuser—Part 2: Validation and Limitations of CFD for Diffuser Flows

1997 ◽  
Vol 119 (4) ◽  
pp. 978-984 ◽  
Author(s):  
F. A. Muggli ◽  
K. Eisele ◽  
M. V. Casey ◽  
J. Gu¨lich ◽  
A. Schachenmann
Keyword(s):  
Turbulence Model ◽  
Flow Separation ◽  
Static Pressure ◽  
Flow Analysis ◽  
Measurement Data ◽  
Pressure Rise ◽  
Pressure Recovery ◽  
Navier Stokes ◽  
Vaned Diffuser ◽  
Highly Loaded

This paper describes an investigation into the use of CFD for highly loaded pump diffuser flows. A reliable commercial Navier-Stokes code with the standard k-ε turbulence model was used for this work. Calculations of a simple planar two-dimensional diffuser demonstrate the ability of the k-ε model to predict the measured effects of blockage and area ratio on the diffuser static pressure recovery at low loading levels. At high loading levels with flow separation the k-ε model underestimates the blockage caused by the recirculation in the flow separation region and overestimates the pressure recovery in the diffuser. Three steady-state calculations of a highly loaded vaned diffuser of a medium specific speed pump have been carried out using different inlet boundary conditions to represent the pump outlet flow. These are compared to LDA measurement data of the flow field and demonstrate that although the Navier-Stokes code with the standard k-ε turbulence model is able to predict the presence of separation in the flow, it is not yet able to accurately predict the static pressure rise of this highly loaded pump diffuser beyond the flow separation point.

A Study on Impeller-Diffuser Interaction—Part I: Influence on the Performance

2003 ◽  
Vol 125 (1) ◽  
pp. 173-182 ◽  
Author(s):  
Kai U. Ziegler ◽  
Heinz E. Gallus ◽  
Reinhard Niehuis
Keyword(s):  
Flow Field ◽  
Field Configuration ◽  
Test Case ◽  
Vaned Diffuser ◽  
Flow Losses ◽  
Extensive Test ◽  
Radial Gap ◽  
Operating Points ◽  
Vane Angle ◽  
Probe Measurements

The interaction between impeller and diffuser is considered to have strong influence on the flow in centrifugal compressors. However, the knowledge about this influence is still not satisfying. This two-part paper presents an experimental investigation of the effect of impeller-diffuser interaction on the unsteady and the time averaged flow field configuration in impeller and diffuser and the performance of these components. The flat wedge vaned diffuser of the investigated compressor allows an independent adjustment of diffuser vane angle and radial gap between impeller exit and diffuser vane inlet. Attention is mainly directed to the radial gap, as it determines the intensity of the impeller-diffuser interaction. Part I deals with the integral flow losses and the diffusion in impeller, diffuser and the entire compressor. An extensive test series with steady probe measurements at impeller exit and diffuser exit was performed at 10 different diffuser geometries and different operating points. The results show that in most cases smaller radial gaps are leading to a more homogeneous flow field at diffuser vane exit and to a higher diffuser pressure recovery resulting in a higher compressor efficiency. On the other hand, impeller efficiency is hardly affected by the radial gap. In Part II, measurements with a laser-2-focus velocimeter are presented illuminating the reasons for the effects found. The experimental results are published as an open CFD test case under the name “Radiver.”

Internal Flow Analysis in a Two-Channel Pump Used for Salt Transportation

2018 ◽  
Author(s):  
Jiaqi Wang ◽  
Xianwu Luo ◽  
Wanming Li ◽  
Bin Ji
Keyword(s):  
Particle Concentration ◽  
Flow Analysis ◽  
Internal Flow ◽  
Leading Edge ◽  
Pressure Side ◽  
Operation Condition ◽  
Static State ◽  
Erosion Risk ◽  
Salt Particle ◽  
Blade Leading Edge

Two-channel pumps usually have very complicated flow field due to the special impeller geometry. The present paper treats the internal flow analysis based on numerical simulation so as to investigate the pumping performance and passage erosion for a two-channel centrifugal pump used for transporting salt particles. The static state flows are calculated by applying RANS method and k-omega SST turbulence model. The numerical results indicate that there are strong circulation flows near the impeller inlet and blade pressure side, and zones with high turbulent kinetic energy near impeller exit when the pump is operated under the designed flow rate i.e. Qd. Pressure decay is also found at the rear part of blade pressure side. At the operation condition of 1.3Qd, the internal flow becomes better. Further, the numerical analysis based on Eulerian-Lagrangian method shows the trajectory of salt particle, salt particle concentration and erosion rate in the pump. It is noted that the salt particles go smoothly in the flow passage due to the large section size of the pump, and there is severe erosion at the blade leading edge and the wall of volute casing due to strong impingement and high particle concentration. Thus, these areas such as blade leading edge and the wall of volute casing are the zones with high erosion risk in the two-channel pump.

A Numerical Study on Performances of Centrifugal Compressor Stages With Different Radial Gaps

2000 ◽  
Author(s):  
K. Sato ◽  
L. He
Keyword(s):  
Centrifugal Compressor ◽  
Stokes Equations ◽  
Numerical Study ◽  
Axial Compressor ◽  
Navier Stokes ◽  
Centrifugal Impeller ◽  
Vaned Diffuser ◽  
Navier Stokes Equations ◽  
Performance Predictions ◽  
Radial Gap

A numerical study of 3D unsteady flows in centrifugal compressor stages solving the Navier-Stokes equations is presented. The emphasis is on the effect of the radial gap between blade rows on the aerodynamic performance. In the numerical tests, Krain’s centrifugal impeller was combined with a DCA (Double Circular Arc) type radial vaned diffuser. The compressor stages with three settings of radial gap ranging from 5 to 15 percent of the impeller trailing edge radius are configured and unsteady flow simulations are carried out to compare the time-averaged efficiencies. The performance predictions show that the efficiency is deteriorated if the radial gap between blade rows is reduced with intensified blade row interaction, which is in contradiction to the general trend for axial compressor stages. In the centrifugal compressors tested, wake chopping by diffuser vanes, which usually benefits efficiency in axial compressor stages, causes unfavourable wake compression through the diffuser passages to deteriorate the efficiency.

A Simulation of the Unsteady Interaction of a Centrifugal Impeller With its Vaned Diffuser: Flows Analysis

1994 ◽  
Author(s):  
W. N. Dawes
Keyword(s):  
Flow Analysis ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Centrifugal Impeller ◽  
Vaned Diffuser ◽  
Time Resolved ◽  
High Loss ◽  
Swirl Angle ◽  
Unsteady Interaction ◽  
Unsteady Effects

The aim of this paper is to help advance our understanding of the complex, three-dimensional, unsteady flow associated with the interaction of a splattered centrifugal impeller and its vaned diffuser. A time-resolved simulation is presented of the Krain stage performed using a time-accurate, 3D, unstructured mesh, solution-adaptive Navier-Stokes solver. The predicted flowfield, compared with experiment where available, displays a complex, unsteady interaction especially in the neighbourhood of the diffuser entry zone which experiences large periodic flow unsteadiness. Downstream of the throat, although the magnitude of this unsteadiness diminishes rapidly, the flow has a highly distorted three-dimensional character. The loss levels in the diffuser are then investigated to try and determine how time-mean loss levels compare with the levels expected from “equivalent” steady flow analysis performed by using the circumferentially averaged exit flow from the impeller as inlet to the diffuser. It is concluded that little loss could be attributed directly to unsteady effects but rather that the principle cause of the rather high loss levels observed in the diffuser is the strong spanwise distortion in swirl angle at inlet which initiates a strong hub/comer stall.

Flow Analysis for Optimal Configuration of Hemoperfusion Device

1987 ◽  
Vol 10 (2) ◽  
pp. 115-120
Author(s):  
V. Chang ◽  
A. Battistin ◽  
R. Rodrigue ◽  
T.M.S. Chang
Keyword(s):  
Cross Section ◽  
Activated Charcoal ◽  
Flow Analysis ◽  
Flow Characteristics ◽  
Vertical Cross Section ◽  
Two Dimensional ◽  
Cylindrical Container ◽  
Flow Configuration ◽  
Normal Configuration ◽  
Inlet Tube

The objective of this experiment was to determine the flow characteristics of a hemoperfusion device. The standard device consists of a cylindrical container which is tapered towards the outlet end. Flow enters the column through a small inlet tube into the wide frontal area of the column. Having passed through the column containing collodian coated activated charcoal spheres, it leaves by the tapered outlet. In order to achieve our aim, we designed and built a two-dimensional plexiglass model consisting of a vertical cross section of the actual hemoperfusion device. Glass beads were used to simulate the artifi-cal carbon cells and a colored solution was used to enable us to visualize the flow. In the normal configuration, it was determined that stagnation and channelling were present. The model was then analysed in the inverse configuration. This way, flow inlet is through the tapered end and flow outlet is towards the wider cylindrical end. This inverse flow configuration improved the flow characteristics and eliminated most of the channelling and stagnation.

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