Abstract
Abstract While significant advances have come about for turbomachinery off-design performance characterization using computational fluid dynamics (CFD), the need for quick performance estimates at challenging off-design conditions still requires the use of lower-order models, such as mean-line analyses and through-flow tools. These inviscid tools require blade performance correlations formulated in terms of loss and turning angle as a function of blade geometric and aerodynamic parameters. Traditionally, such correlations have relied on the empirical data from blade cascade tests at nominal incidence conditions. This limitation on the applicability of the blade correlations has caused performance modeling of the sub-idle regime to be off-limits to this type of correlation-based approaches. This paper addresses the development of blade loss and deviation models applicable to the sub-idle regime using a parametric numerical approach. 2D CFD results are used to generate a model that is then applied to mean-line and through-flow analyses aimed at predicting the sub-idle map of an axial flow compressor. The model proves to be a valuable tool for quick sub-idle performance estimates and allows existing correlation-based performance prediction methods to be extended into the sub-idle regime.
Highlights
Operation below the idle speed subjects compressor blading to negative incidences far from the design point
A model for modern compressor blades subjected to high negative incidence has been generated in terms of loss coefficient and deflection angle
This could allow for early prediction of compressor sub-idle performance, which is critical to ensure whole-engine ground start and inflight relight requirements are met
Summary
Operation below the idle speed subjects compressor blading to negative incidences far from the design point. The extent of negative incidence is especially severe for downstream stages, where the lack of compression coupled to a convergent flow path causes the axial velocity to increase, while the rotor velocity remains relatively low, resulting in high flow coefficients with the subsequent drop in loading. Such off-design conditions are typically termed sub-idle operation [1]. In the case of the axial flow compressor, throughflow tools and mean-line methods are typically used to solve the conservation equations in a reduced form, employing blade performance correlations in the form of loss coefficients and deviation angles to include viscous effects stemming from the presence of blade-rows
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