Matthieu Boileau

Ignition sequence of an annular multi-injector combustor

Ignition is a critical process in combustion systems. In aeronautical combustors, altitude relight capacities are required in case of accidental extinction of the chamber. A simultaneous study of light-round ignition in an annular multi-injector combustor has been performed on the experimental and numerical sides. This eort allows a unique comparison to assess the reliability of Large-Eddy Simulation (LES) in such a conguration. Results are presented in uid dynamics videos.

Simulation of the Ignition Process in an Annular Multiple-Injector Combustor and Comparison With Experiments

Ignition is a problem of fundamental interest with critical practical implications. While there are many studies of ignition of single injector configurations, the transient ignition of a full annular combustor has not been extensively investigated, mainly because of the added geometrical complexity. The present investigation combines simulations and experiments on a complete annular combustor. The setup, developed at EM2C laboratory, features sixteen swirl injectors and quartz walls allowing direct visualization of the flame. High speed imaging is used to record the space time flame structure and study the dynamics of the light-round process. On the numerical side, massively parallel computations are carried out in the LES framework using the Filtered Tabulated (F-TACLES) flamelet model. Comparisons are carried out at different instants during the light-round process between experimental data and results of calculations. It is found that the simulation results are in remarkable agreement with experiments provided that the thermal effects at the walls are considered. Further post-processings indicate that the flame burning velocity and flame front geometry are close to those found in the experiment. This analysis confirms that the LES framework used for these calculations and the selected combustion model are adequate for such calculations but that further work is needed to confirm that ignition prediction can be used reliably over a range of operating parameters.Copyright

Robust Numerical Coupling of Pressure and Pressureless Gas Dynamics Equations for Eulerian Spray DNS and LES

Large eddy simulation (LES) and direct numerical simulation (DNS) of polydisperse evaporating sprays with Eulerian models are very promising tools for high performance computing of combustion applications since they are able to predict the turbulent dispersion and evaporation. However, the spray system of conservation equations has a convective part which is similar either to gas dynamics Euler equations with a real gas type state law or to the pressureless gas dynamics (PGD), depending on the local flow regime and droplet Stokes number; so they usually involve singularities due to model closure assumptions and require dedicated numerical schemes. The present contribution introduces a new generation of numerical methods based on relaxation schemes which are able to treat both PGD and general gas dynamics as well as to cope in a robust manner with vacuum zones and natural singularities of the resulting system of conservation equations. The approach relies on the coupling between a relaxed model for PGD and...

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.