| Summary: | A fully elliptic computational method for the analysis of steady viscous flow
in high speed subsonic centrifugal compressor impellers with tip leakage, is
presented. A generalised curvilinear, non-orthogonal grid is utilised and the timeaveraged
Navier-Stokes equations are transformed and expressed in a fully
conservative form. The discretisation of the governing equations is performed
through finite volume integration. The solution procedure employs a non-staggered
variable arrangement and a SIMPLE based method for coupling the velocity and
pressure fields. The turbulence effects are simulated with the use of the k-e model,
modified to account for rotation and streamline curvature, and the near-wall viscous
phenomena are modelled through the wall function method.
The numerical model is implemented for the flow prediction in a series of
two and three dimensional test cases. Incompressible flow predictions in twodimensional
cascades and three-dimensional ducting systems with different
geometrical features and inlet conditions are initially performed and the numerical
results are compared against available experimental data. The final objective of the
present study is achieved through the comparative study of the predictions obtained
against the results of Eckardt's experimental investigation of the viscous
compressible flow in a high speed radial impeller operating at design condition and
in a backswept impeller at design and off-design conditions. In addition, the flow is
simulated in the passages of the Rolls Royce GEM impeller which was tested at
Cranfield at design and off-design flow rates.
A jet/wake pattern was discerned in all the simulated centrifugal compressor
cases and a good overall agreement was achieved with the measured wake formation
and development; and, encouraging results were obtained on the evolution of the
secondary flows. The tip leakage effects influenced the loss distribution, the size and
the location of the wake flow pattern at the rotor exit. The effects of the flow mass
rate on the detailed flow pattern and on the compressor performance have been well
represented. In certain cases, the quality of the present predictions is an
improvement over that obtained by other "state-of-the-art" Navier-Stokes solvers.
In conclusion, the developed finite volume flow model has captured a large number
of complex flow phenomena encountered in the tested impellers and is expected to
provide a useful aerodynamic analysis tool for stationary or rotating, axial or radial
turbomachinery components.
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