Mouret, Gaëlle. Adaptation of phaselagged boundary conditions to largeeddy simulation in turbomachinery configuration. PhD, Dynamique des fluides, Institut National Polytechnique de Toulouse, 2016

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Abstract
The more and more restrictive standards in terms of fuel consumption and pollution for aircraft engines lead to a constant improvement of their design. Numerical simulations appear as an interesting tool for a better understanding and modeling of the turbulent phenomena which occur in turbomachinery. The largeeddy simulation (LES) of a turbomachinery stage at realistic conditions (Mach number, Reynolds number...) remains out of reach for industrial congurations. The phaselagged method, widely used for unsteady Reynoldsaveraged NavierStockes (URANS) calculations, is a good candidate to reduce the computational cost. However, it needs to store the signal at all the boundaries over a full passage of the opposite blade. A direct storage of the information being excluded given the size of the mesh grid and timesteps involved, the most used solution currently is to decompose the signal into Fourier series. This solution retains the fundamental frequency of the signal (the opposite blade passage frequency) and a limited number of harmonics. In the frame of a LES, as the spectra are broadband, it implies a loss of energy. Replacing the Fourier series decomposition by a proper orthogonal decomposition (POD) allows the storage of the signal at the interfaces without making any assumptions on the frequency content of the signal, and helps to reduce the loss of energy caused by the phase lagged method. The compression is done by removing the smallest singular values and the associated vectors. This new method is first validated on the URANS simulations of turbomachinery stages and compared with Fourier seriesbased conditions and references calculations with multiple blades per row. It is then applied to the large eddy simulation of the flow around a cylinder. The error caused by the phaselagged assumption and compression are separated and it is showed that the use of the POD allows to halve the filtering of the velocity fluctuations with respect to the Fourier series, for a given compression rate. Finally, the large eddy simulation of a compressor stage with POD phaselagged conditions is carried out to validate the method for realistic turbomachinery configurations.
Item Type:  PhD Thesis 

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Institution:  Université de Toulouse > Institut National Polytechnique de Toulouse  Toulouse INP (FRANCE) 
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Research Director:  Gourdain, Nicolas and Castillon, Lionel 
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Deposited On:  02 Nov 2016 13:55 
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