Transonic Axial Compressors Loss Correlations: Part I — Analysis and Update of Loss Models

The quest for greener, more efficient aircraft engines, along with the continuous growth of the aviation sector expected in the next decades, are the main drivers for the development of innovative aero-engine configurations to reduce CO2 and NOx emissions. To achieve such goal, new compression system technologies are currently being designed and investigated. These emerging components are characterized by atypical and complex flow fields, requiring to explore, since the early stages of the design process, a wide design space in quest of the highest efficiency regions. Thanks to their simplicity, reduced order loss models are a valuable preliminary design tool that can be easily parametrized to provide a deep survey of the design space. Nevertheless, they often rely on semi-empirical correlations, whose validity range is often too narrow or, in general, not matching with the flow conditions of interest for modern turbomachinery applications.

The present work focuses on the entropy generation mechanisms occurring in modern transonic axial compressors. In particular, it aims at defining a set of loss correlations capable of estimating the contribution and the span wise distribution of the various loss sources, which could readily be employed in the analysis and design process of state-of-art transonic axial compressors.

In part I, the main entropy generation mechanisms are described together with a review of the most commonly employed loss modelling approaches. Focus is set on those based on the most solid physical bases and that proved robustness toward input parameters. The most promising loss models are then deeper investigated and updated, through physically based considerations, to increase both the accuracy of their predictions and their ranges of validity. In particular, the contributions considered in this study are profile loss, shock loss, end-wall loss, and tip-clearance loss.

In part II, the accuracy of the selected loss models is assessed through experimental and numerical validation, using available data on a state-of-art transonic low aspect ratio compressor stage, whose characteristics lay outside the correlations’ validity ranges. A detailed description of the implementation of the various loss models will be also provided.