By W. Rodi and N. Fueyo (Eds.)
Read or Download Engineering Turbulence Modelling and Experiments 5. Proceedings of the 5th International Symposium on Engineering Turbulence Modelling and Measurements Mallorca, Spain, 16–18 September, 2002 PDF
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Additional resources for Engineering Turbulence Modelling and Experiments 5. Proceedings of the 5th International Symposium on Engineering Turbulence Modelling and Measurements Mallorca, Spain, 16–18 September, 2002
Of interest here, however, is not the absolute level of accuracy of the predictions but the trend with variation of flow. Despite the scatter in absolute level of efficiency, all of the simulations show a roughly linear increase in efficiency with flow giving peak efficiency close to the choke point, roughly in agreement with the trend from the test data. This behaviour of transonic compressor rotors had previously been explained by Freeman and Cumpsty (1989) using a relatively simple one-dimensional control volume analysis of the inlet region of a transonic axial cascade.
Design systems can then be automated to produce blade profiles with similar loading distributions and boundary layer shape factor according to specified design rules derived form those good designs previously used, Gallimore (1999). These arguments are very useful for designers to justify their lack of interest in turbulence modelling but cannot be carried too far. There are, of course, many critical aspects of the flow that are fundamentally related to the turbulence model, and where accurate predictions of near-wall flows would be more than welcome by most designers - in particular for separation, heat transfer, losses and wall friction.
Once calibrated in this way, the corrections are then used for a new design. Secondly, the good designer carefully considers only the differences in the simulations between the various competing designs and uses these to rank the designs. Thirdly, designers can use CFD to copy features into a new design from an earHer good design (perhaps even without detailed imderstanding of the real flow mechanisms responsible for the good performance). For example, a velocity distribution on a blade profile which experience shows gives rise to low losses (such as front loading of a subsonic compressor blade, Ginder (1991)) may be repeatedly used in new designs even if a full understanding of the mechanisms leading to the low loss is unavailable.