The need was identified to develop an analytical performance prediction code for subsonic multistage
axial compressors that can be included in network analysis software. It was found that
performance calculations based on an elementary one-dimensional meanline prediction method
could achieve remarkable accuracy, provided that sound models are used for the losses, deviation
and the onset of rotating stall. Consequently, this study focuses on gaining more expertise on the
modelling of losses in such compressors through investigating the mechanisms responsible, the
methods of predicting them, their implementation and possible usage.
Internal losses are seen as mechanisms that increase the entropy of the working fluid through the
compressor and it was found that, at a fundamental level, all internal losses are a direct result of
viscous shearing that occurs wherever there are velocity gradients. Usually the methodology
employed to predict the magnitudes of these mechanisms uses theoretically separable loss
components, ignoring the mechanisms with negligible velocity gradients. For this study these
components were presented as: Blade profile losses, endwall losses including tip leakage and
secondary losses, part span shroud losses, other losses, losses due to high subsonic Mach numbers
and incidence loss. A preliminary performance prediction code, with the capability of
interchanging of the different loss models, is presented. Verification was done by comparing the
results with those predicted by a commercial software package and the loss models were
evaluated according to their ease of implementation and deviation from the predictions of the
commercial package. Conclusions were made about the sensitivity of performance prediction to
using the different loss models.
Furthermore, the combination of loss models that include the most parameters and gave the best
comparison to the commercial software predictions was selected in the code to perform
parametric studies of the loss parameters on stage efficiency. This was done to illustrate the
ability of the code for performing such studies to be used as an aid in understanding compressor
design and performance or for basic optimization problems.
It can therefore be recommended that the preliminary code can be implemented in an engineering
tool or network analysis software. This may however require further verification, with a broader
spectrum of test cases, for increased confidence as well as further study regarding aspects like
multi-stage annulus blockage and deviation / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2004.
| Identifer | oai:union.ndltd.org:NWUBOLOKA1/oai:dspace.nwu.ac.za:10394/431 |
| Date | January 2003 |
| Creators | Swift, William James |
| Publisher | North-West University |
| Source Sets | North-West University |
| Detected Language | English |
| Type | Thesis |
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