Olivier Gicquel

Three-dimensional boundary conditions for numerical simulations of reactive compressible flows with complex thermochemistry

The Navier-Stokes characteristic boundary conditions (NSCBC) is a very efficient numerical strategy to treat boundary conditions in fully compressible solvers. The present work is an extension of the 3D-NSCBC method proposed by Yoo et al. and Lodato et al. in order to account for multi-component reactive flows with detailed chemistry and complex transport. A new approach is proposed for the outflow boundary conditions which enables clean exit of non-normal flows, and the specific treatment of all kinds of edges and corners is carefully addressed. The proposed methodology is successfully validated on various challenging multi-component reactive flow configurations.

Multicomponent real gas 3-D-NSCBC for direct numerical simulation of reactive compressible viscous flows

Abstract The topic of this paper is to propose an extension of the classical one-dimensional Navier–Stokes boundary conditions (1-D-NSCBC) for real gases initially developed by Okong’o and Bellan [1] to a 3-D-NSCBC formulation based on the work of Lodato et al. [2] and Coussement et al. [3] . All the differences due to the real gas formulation compared to the perfect gas formulation proposed in [3] are emphasized. A new way of determining the pressure relaxation coefficient is introduced for handling transcritical flows crossing the boundary. The real gas 3-D-NSCBC are then challenged on several test cases: a two-dimensional subsonic vortex convection, a subsonic supercritical bubble convection and a flame vortex interaction. All these test cases are performed by direct numerical simulation of multicomponent flows. It shows the stability of the boundary conditions without creating any numerical artifact.

A Method To Accelerate LES Explicit Solvers Using Local Time-Stepping

a large disparities of geometrical length scales are often encountered. Inside a combustor, for example, the ratio between the diameter of the injection holes and the size of the entire combustion chamber may present several orders of magnitude. When considering an explicit solver for fully compressible Navier-Stokes equations, the global time step is constrained through a CFL-like condition by the size of the smallest cells in the overall computational domain. Local renement of the injector leads to an inhomogeneous mesh and the former restriction drastically alters the overall solver eciency. A new local time-stepping (LTS) method is proposed to address this issue. The domain is divided into subgrids composed of cells that have similar sizes. Flow equations are simultaneously advanced on each subgrid which have a local time step adapted to satisfy the local CFL condition. The accuracy of the method has been veried on a simple convection case using a test code. The method has also been implemented in a large eddy simulation (LES) explicit solver and successfully tested for an acoustic wave propagation. It has been nally used in the two-dimensional large eddy simulation of a turbulent jet.

A Filtered Tabulated Chemistry Model for Large Eddy Simulation of Reactive Flows

A new model called F-TACLES (Filtered Tabulated Chemistry for LES) is developed to introduce tabulated chemistry methods in LES of turbulent premixed combustion. The main objective is to recover the correct propagation speed of the flltered flame front when the sub-grid scale wrinkling vanishes. The filtered flame structure is mapped by 1-D filtered laminar premixed flames. The methodology is first applied to 1-D filtered laminar flames. Computations show the capability of the model to recover the laminar flame speed and the correct chemical structure when flame wrinkling is fullyresolved on the LES lter scale. The model is then extended to turbulent regimes by introducing sub-grid scale wrinkling effects on the flame propagation. LESs of a 3-D turbulent premixed flame are performed on dierent grids, with different flame filter sizes. Objectives are to analyze the influence of the grid size, the flame filter size and the sub-grid flame wrinkling on the model performances. All these computations are compared to experimental data.