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Unshrouded rotor tip clearance effects in expander cycle turbines

Helmers, Lennard and Klingmann, Jens LU (2002) 2002 ASME Turbo Expo: Land, Sea and Air In Proceedings of the ASME Turbo Expo
Abstract
Steady flow in axial one-stage turbines is assessed numerically and experimentally. The simulations are performed on coarse meshes using a standard numerical approach (3D, steady state, kε-turbulence model, wall function at solid boundaries). In order to allow for conclusions drawn from these rapid numerical studies, the approach was compared with an explicit LDA (Laser Doppler anemometry) mapping of the velocity field downstream the rotor on a representative turbine stage. A two-component LDA system allowed for measurements of axial and tangential velocity components at varying depth (radius) in the flow channel, Measurements thus correspond to a full plane at constant axial position in the rotating frame of reference of the rotor.... (More)
Steady flow in axial one-stage turbines is assessed numerically and experimentally. The simulations are performed on coarse meshes using a standard numerical approach (3D, steady state, kε-turbulence model, wall function at solid boundaries). In order to allow for conclusions drawn from these rapid numerical studies, the approach was compared with an explicit LDA (Laser Doppler anemometry) mapping of the velocity field downstream the rotor on a representative turbine stage. A two-component LDA system allowed for measurements of axial and tangential velocity components at varying depth (radius) in the flow channel, Measurements thus correspond to a full plane at constant axial position in the rotating frame of reference of the rotor. Comparison between LDA velocity mapping and CFD results shows good agreement.

A series of subsequent simulations is thus used to judge the impact of varied blade/stage design parameters.

Two turbine layouts are defined for identical operating conditions and shaft power. The flow in the unshrouded rotor blade row is analyzed for the influence of varying tip clearance size and the dependency on stage velocity triangles. – Known correlations for tip clearance losses (typically used in mean line predictions) are used, though the blade row geometry considered is beyond the limits the correlations are intended for. The absolute loss level found in CFD simulations differs significantly from what is expected when using loss correlations. Still the variation with tip gap size is predicted well by some of the investigated models. As dependency of tip clearance losses on stage velocity triangles is considered, none of the tested correlations gives results consistent with the numerical simulations. The use of standard correlations ‘beyond the limits’ is thus considered to introduce high uncertainty.

Due to the good consistency between LDA and numerical results, the conclusions are considered to be valid for stage designs similar to the ones analyzed. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
loss correlation, tip clearance, CFD, LDA
in
Proceedings of the ASME Turbo Expo
publisher
American Society Of Mechanical Engineers (ASME)
conference name
2002 ASME Turbo Expo: Land, Sea and Air
external identifiers
  • other:GT2002-30338
  • scopus:0036998178
language
English
LU publication?
yes
id
67a17e64-0f4c-4279-8f3d-0f94bfc8cbd2 (old id 645303)
date added to LUP
2008-02-27 10:48:56
date last changed
2017-01-01 07:56:41
@inproceedings{67a17e64-0f4c-4279-8f3d-0f94bfc8cbd2,
  abstract     = {Steady flow in axial one-stage turbines is assessed numerically and experimentally. The simulations are performed on coarse meshes using a standard numerical approach (3D, steady state, kε-turbulence model, wall function at solid boundaries). In order to allow for conclusions drawn from these rapid numerical studies, the approach was compared with an explicit LDA (Laser Doppler anemometry) mapping of the velocity field downstream the rotor on a representative turbine stage. A two-component LDA system allowed for measurements of axial and tangential velocity components at varying depth (radius) in the flow channel, Measurements thus correspond to a full plane at constant axial position in the rotating frame of reference of the rotor. Comparison between LDA velocity mapping and CFD results shows good agreement. <br/><br>
A series of subsequent simulations is thus used to judge the impact of varied blade/stage design parameters.<br/><br>
Two turbine layouts are defined for identical operating conditions and shaft power. The flow in the unshrouded rotor blade row is analyzed for the influence of varying tip clearance size and the dependency on stage velocity triangles. – Known correlations for tip clearance losses (typically used in mean line predictions) are used, though the blade row geometry considered is beyond the limits the correlations are intended for. The absolute loss level found in CFD simulations differs significantly from what is expected when using loss correlations. Still the variation with tip gap size is predicted well by some of the investigated models. As dependency of tip clearance losses on stage velocity triangles is considered, none of the tested correlations gives results consistent with the numerical simulations. The use of standard correlations ‘beyond the limits’ is thus considered to introduce high uncertainty.<br/><br>
Due to the good consistency between LDA and numerical results, the conclusions are considered to be valid for stage designs similar to the ones analyzed.},
  author       = {Helmers, Lennard and Klingmann, Jens},
  booktitle    = {Proceedings of the ASME Turbo Expo},
  keyword      = {loss correlation,tip clearance,CFD,LDA},
  language     = {eng},
  publisher    = {American Society Of Mechanical Engineers (ASME)},
  title        = {Unshrouded rotor tip clearance effects in expander cycle turbines},
  year         = {2002},
}