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 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 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”.

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.”

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.

CFD Analysis of Unsteady Flow Interactions in a Centrifugal Compressor Stage

2000 ◽  
Author(s):  
A. Koumoutsos ◽  
A. Tourlidakis ◽  
R. L. Elder
Keyword(s):  
Steady State ◽  
Flow Field ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Fourier Transforms ◽  
Flow Analysis ◽  
Design Flow ◽  
Compressor Stage ◽  
Vaned Diffuser ◽  
Centrifugal Compressor Stage

This paper describes the unsteady flow analysis in a centrifugal compressor stage using a three dimensional CFD algorithm. The flow unsteadiness arising from the interaction between the impeller and the diffuser has been analysed using an algorithm suitable for equal or multiple number of rotor and diffuser blades. The multi-block, structured grid CFD code TASCflow was used as a basis and algorithm development was undertaken to provide the required capability of modelling the unsteady interactions of the impeller and the diffuser. The centrifugal compressor stage studied consists of an impeller with splitters and a vaned diffuser. The results presented are for off-design flow conditions where some experimental results were available for comparison. The results obtained for the steady-state model show a good agreement with the measurements. In general the unsteady flow field obtained show a reasonable agreement with experimental data and demonstrates significant differences when compared to the steady state results especially in terms of the velocity field. A detailed analysis of the unsteady flow field is carried out using Fourier transforms of velocity and pressure at various locations of the flow field and the level of unsteadiness is determined as distributed to various frequencies. The unsteadiness in the impeller passage is much less than in the diffuser where a strong coupling is predicted in the vaneless space.

Investigation of Unsteady Flow Field in a Vaned Diffuser of a Transonic Centrifugal Compressor

2006 ◽  
Vol 129 (4) ◽  
pp. 686-693 ◽  
Author(s):  
Seiichi Ibaraki ◽  
Tetsuya Matsuo ◽  
Takao Yokoyama
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Transonic Compressor ◽  
Inlet Conditions

Transonic centrifugal compressors are used with high-load turbochargers and turboshaft engines. These compressors usually have a vaned diffuser to increase the efficiency and the pressure ratio. To improve the performance of such a centrifugal compressor, it is required to optimize not only the impeller but also the diffuser. However the flow field of the diffuser is quite complex and unsteady because of the impeller located upstream. Although some research on vaned diffusers has been published, the diffuser flow is strongly dependent on the particular impeller exit flow, and some of the flow physics remain to be elucidated. In the research reported here, detailed flow measurements within a vaned diffuser were conducted using a particle image velocimetery (PIV). The vaned diffuser was designed with high subsonic inlet conditions marked by an inlet Mach number of 0.95 for the transonic compressor. As a result, a complex three-dimensional flow with distortion between the shroud and the hub was observed. Also, unsteady flow accompanying the inflow of the impeller wake was confirmed. Steady computational flow analysis was performed and compared with the experimental results.

Investigation of Unsteady Flow Field in Vaned Diffuser of a Transonic Centrifugal Compressor

2006 ◽  
Author(s):  
Seiichi Ibaraki ◽  
Tetsuya Matsuo ◽  
Takao Yokoyama
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Centrifugal Compressor ◽  
Pressure Ratio ◽  
Flow Analysis ◽  
Three Dimensional ◽  
Flow Measurements ◽  
Vaned Diffuser ◽  
Transonic Compressor ◽  
Inlet Conditions

Transonic centrifugal compressors are used with high-load turbochargers and turboshaft engines. These compressors usually have a vaned diffuser to increase the efficiency and the pressure ratio. To improve the performance of such a centrifugal compressor, it is required to optimize not only the impeller but also the diffuser. However the flow field of the diffuser is quite complex and unsteady because of the impeller located upstream. Although some research on vaned diffusers has been published, the diffuser flow is strongly dependent on the particular impeller exit flow, and some of the flow physics remain to be elucidated. In the research reported here, detailed flow measurements within a vaned diffuser were conducted using a particle image velocimetery (PIV). The vaned diffuser was designed with high subsonic inlet conditions marked by an inlet Mach number of 0.95 for the transonic compressor. As a result, a complex three-dimensional flow with distortion between the shroud and the hub was observed. Also, unsteady flow accompanying the inflow of the impeller wake was confirmed. Steady computational flow analysis was performed and compared with the experimental results.

Influence of taper, Reynolds number and Mach number on the secondary flow field of a highly loaded turbine cascade

1997 ◽  
Vol 211 (4) ◽  
pp. 309-320 ◽  
Author(s):  
A Duden ◽  
L Fottner
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Flow Field ◽  
Secondary Flow ◽  
Strong Influence ◽  
Three Dimensional ◽  
Surface Flow ◽  
Secondary Loss ◽  
Secondary Flow Field ◽  
Highly Loaded

The meridional divergence of low-pressure turbines has a strong influence on their secondary flow field. This paper describes experimental and numerical investigations on two highly loaded linear turbine cascades with the same blade profile and stacking but with parallel end walls and divergently tapered end walls respectively. The effects of taper, Reynolds number (1.2 × 105, 5 × 105) and Mach number (0.30, 0.59, 0.80) are discussed. Data were obtained using pneumatic probes, pressure tappings and surface flow visualizations. Calculations were performed with the three-dimensional Navier—Stokes solver BTOB3D. The investigations show a strong influence of the taper on the pressure distribution and an unexpected high rise in secondary loss. In both cascades the secondary loss coefficient rises with reduced Reynolds number and Mach number respectively.

scholarly journals Feasibility Study on Oil Droplet Flow Investigations Inside Aero Engine Bearing Chambers: PDPA Techniques in Combination With Numerical Approaches

1995 ◽  
Author(s):  
A. Glahn ◽  
M. Kurreck ◽  
M. Willmann ◽  
S. Wittig
Keyword(s):  
Numerical Methods ◽  
Flow Field ◽  
Flow Analysis ◽  
Field Analysis ◽  
Oil Droplet ◽  
Droplet Flow ◽  
Aero Engine ◽  
Secondary Air ◽  
Numerical Approaches ◽  
Engine Bearing

The present paper deals with oil droplet now phenomena in aero engine bearing chambers. An experimental investigation of droplet sizes and velocities utilizing a Phase Doppler Particle Analyzer (PDPA) has been performed for the first time in bearing chamber atmospheres under real engine conditions. Influences of high rotational speeds are discussed for individual droplet size classes. Although this is an important contribution to a better understanding of the droplet flow impact on secondary air/oil system performance, an analysis of the droplet flow behaviour requires an incorporation of numerical methods because detailed measurements as performed here suffer from both strong spatial limitations with respect to the optical accessibility in real engine applications and constraints due to the extremely time consuming nature of an experimental flow field analysis. Therefore, further analysis is based on numerical methods. Droplets characterized within the experiments are exposed to the flow field of the gaseous phase predicted by use of our well-known CFD code EPOS. The droplet trajectories and velocities are calculated within a Lagrangian frame of reference by forward numerical integration of the particle momentum equation. This paper has been initiated rather to show a successful method of bearing chamber droplet flow analysis by a combination of droplet sizing techniques and numerical approaches than to present field values as a function of all operating parameters. However, a first insight into the complex droplet flow phenomena is given and specific problems in bearing chamber heat transfer are related to the droplet flow.

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