Final work : Assessment of throughflow closure models for a modern axial compressor

Abstract

This master’s thesis is dedicated to the assessment of various closure models for Navier- Stokes-based throughflow modelling. This is done in the context of a high-subsonic flow compressor with highly loaded blades of three-dimensional design. The averaging cascade of Adamczyk is employed to identify the unclosed terms in the Navier-Stokes throughflow equations. The terms of major importance are identified based on the literature and related to the physical flow features that they represent. Empirical models for the blade profile loss, deviation angle, tip leakage loss, and end-wall boundary layer are then selected from the literature. The accuracy of these models is assessed through three approaches. First, two-dimensional blade-to-blade computational fluid dynamics simulations of a stator blade row are performed to analyse various empirical models for profile loss and deviation. This analysis confirms that compressibility effects need to be accounted for at elevated Mach number, particularly for prediction at off-design incidence angle. The profile loss model of König is shown to be more accurate than the model of Lieblein in this respect. The deviation angle models of Carter, Lieblein and Wu Dong-Run are shown to give reasonable predictions at design incidence angle. The second approach is to feed the empirical models with circumferentially averaged results of three-dimensional computational fluid dynamics simulations of the entire compressor. This reveals the deficiency of König’s model for incidence angles much smaller than the predicted minimum loss incidence angle. Two tip leakage models of Lakshminarayana are also assessed in this context. In the third approach, the empirical models are implemented in a Navier-Stokes throughflow model. The resulting radial distributions of loss and deviation are analysed for all blade rows at nominal operating conditions. Finally, the results are discussed in terms of isentropic efficiency, pressure ratio, and total temperature ratio of the entire compressor operating at off-design conditions.