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PhD Defense: Sophie LE BRAS – Wall modeling and non-conforming grid interfaces for computational aeroacoustics with a high-order numerical approach

  Thursday 24 March 2016 at 13h30

  Phd Thesis       SALLE DE CONFÉRENCE JEAN-CLAUDE ANDRÉ    

Abstract:

This thesis is devoted to the development of numerical methods to predict jet noise using Large-Eddy Simulation (LES). The LES approach used in this work relies on high-order low-dissipation and low-dispersion implicit finite-volume schemes for spatial discretization. It allows the direct calculation of acoustic sources in turbulent flows and the propagation of sound waves with accuracy. Two numerical methods are developed in order to facilitate the LES computations. The first method focuses on using wall modeling in the near-wall regions instead of resolving the boundary layers. An analytical wall model is combined with the high-order schemes for spatial discretization. A specific spatial discretization, based on a ghost cell reconstruction, is proposed near the walls. Its performance is assessed by performing the LES of a turbulent channel flow at a Mach number of 0.2 and a friction Reynolds number of 2,000, and the LES of an isothermal subsonic round jet at a Mach number of 0.6 and a Reynolds number based on the jet diameter of 570,000. The aerodynamic and the acoustic properties of the flows are in agreement with the direct numerical simulation data and the experimental results of the litterature. The second method deals with the development of a treatment at the non-conforming grid interfaces. Non-conforming grids involve discontinuous block interfaces, allowing the use of simplified meshes for the computations. The proposed treatment ensures the compatibility between the spatial discretization schemes and non-conforming meshes. Particular attention is paid to meet the accuracy requirements imposed in computational aeroacoustics. This treatment relies on meshless interpolations. Its validity is evaluated by simulating a vortex convection and a mixing layer development in two dimensions. The results show that the treatment does not produce significant spurious numerical waves nor disturb the flow development near the grid interfaces.

Jury:

Xavier GLOERFELT              ENSAM                                               Referee

Eric SERRE                            UNIVERSITÉ AIX-MARSEILLE        Referee

Hugues DENIAU                   ONERA                                               Member

Fabien WLASSOW                AIRBUS                                              Member

Guillaume DAVILLER           CERFACS                                            Member

Sébastien DECK                   ONERA                                               Member

Eric LAMBALLAIS                 ENSMA Poitiers                                 Member

Christophe BOGEY               ECOLE CENTRALE DE LYON          Advisor