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This study presents the assessment of a viscous throughflow model applied to high subsonic flow for two modern compressors designed by Safran Aero Boosters. Blades forces terms resulting from the averaging of the Navier-Stokes equations are computed using correlations from the literature. In particular, the optimal incidence angle, the profile loss and the deviation angle are estimated with empirical models. However, these correlations are not adapted for modern blade geometries and high Mach number flows. Therefore, the first aim of this work has been to assess the validity of the correlation predictions using a blade-to-blade approach. The three correlations have been investigated separately. The comparisons between the correlation predictions and the results of the cascade simulations used as reference revealed the necessity to calibrate the correlations. As a result of this observation, the optimal incidence angle is first corrected by adding a correction factor. The predictions for the profile losses are accurate for the two compressors once the angle of incidence is corrected. This study mainly focuses on the calibration of the deviation angle. Three strategies are investigated to calibrate the deviation angle correlation. The first calibration tunes the empirical coefficients of the correlation via an algorithm. The second calibration revises the terms included in the correlation and adds a contribution. These two strategies prove successful. The third method, based on a genetic algorithm, attempts to generate a polynomial function depending on the geometric parameters to characterise the deflection angle. This third method still needs to be tuned for a higher number of cases. The first two calibrated correlations are implemented in the throughflow model, and the resulting performance maps are analysed by comparison with higher-fidelity results. The modified correlations yield significant improvements in performance predictions. A sensibility analysis is finally carried out based on the stagger angle variability. The comparison with higher-fidelity results demonstrates the validity and reliability of the throughflow model with the two enhanced correlations.
Throughflow model --- Correlation --- Deviation angle --- Profile loss --- Optimal incidence --- Ingénierie, informatique & technologie > Ingénierie aérospatiale
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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.
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This master thesis describes the assessment of secondary flows model for a viscous throughflow solver in the scope of two test cases. They are the classic axial compressor stage CME2 and a multi-stage axial low-pressure compressor with highly loaded blades developed by Safran Aero Boosters. The review of the literature for secondary flow models has shown that geometrical and flow parameters are of great importance in the formulation of these correlations. By the comparison with three-dimensional RANS simulations, the assessment of the reliability of different types of correlations for design and off-design conditions, various boundary layer thicknesses and blade geometries has shown that the distributions for the total pressure loss coefficient and deviation angle from Roberts are providing the most promising results. However, the implementation of Roberts’ correlations in theirs current forms in the throughflow model has not shown a substantial improvement in terms of the prediction of performance maps for the two test cases. Even tough secondary flows physics are still hardly predictable, such models can be completed by additional terms and coefficients for improving preliminary design applications. Some suggestions are discussed at the end of this thesis.
computational fluid dynamics --- meridional plane --- 3D blades --- axial compressor --- Adamczyk's cascade --- deviation angle --- profile loss --- RANS --- throughflow model --- secondary flows --- Ingénierie, informatique & technologie > Ingénierie aérospatiale
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