Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

With the customer’s increasing requirements on engine performance, the optimisation of every engine component is critical to maximize the performance. Therefore, the secondary effects have to be taken into account, to understand where the sources of losses come from and how reduce them. Among the many secondary effects that exist in compressors, leakage flows between stationary and rotating parts are one of the main sources of losses in turbomachinery. The standard method to take into account leakage flows relies on chimera grids of rectangular cavities at the bottom of which a mass flow and a flow direction are imposed. The evolution of the design methods gives rise to boosters geometries with ascending and descending flow path for which the method was not calibrated. Thus, a new advanced modelling of higher fidelity is needed to evaluate leakage flows and to analyse their behaviour.
The complete modelling of seal cavities has highlighted that the leakage flow rate was twice overestimated by the standard modelling. Moreover, the advanced modelling increases the compressor performance thanks to its higher fidelity. Near the stall conditions, the higher-fidelity results of the advanced modelling show that the flow behaviour at the stator foot is better than predicted by the standard modelling. However, this result does not allow to conclude if the stator is weaker on the foot or on the head. However, simulations based on the advanced modelling are costly compared to the standard modelling. Therefore, an analytical model based on the Stodola formula has been developed in order to approximate the leakage-flow rate and the windage heating. The calibration of the formula for two engines has shown that the discharge coefficient CD only depends on the geometric shape of the fin head.
Finally, a trade-off between the computation cost and the fidelity of the simulations is developed through a simplified modelling of cavities. This modelling was built for further optimisation of the corner-radius shape of the upstream cavity opening. The geometry of the upstream cavity seal is reproduced since it has a critical effect on the compressor performance. This simplified modelling gives faithful results compared to the advanced modelling on the compressor performance.

CFD modelling of leakage flows in low-pressure compressors --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

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

Choose an application

• Reference Manager
• EndNote
• RefWorks (Direct export to RefWorks)

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