Compressible and Incompressible Large Eddy Simulation of a Premixed Dump Combustor

Premixed combustion in the ORACLES dump combustor is investigated by Large-Eddy Simulation. The results are compared with experimental measurements of mean and fluctuating velocities at various points inside the combustor. The LES is performed with the in-house PsiPhi code, which has been modified to account for compressibility so that flame-acoustic interactions can be studied. The modifications include the use of proper boundary conditions that are based on the Navier-Stokes Characteristic Boundary Conditions (NSCBC) [1]. A fixed velocity and temperature inlet as well as a partially reflecting outlet are selected. The reaction rate is modelled using algebraic expressions for the generalised flame surface density (FSD) Σ_gen. A selection of FSD models [2] were previously tested using the incompressible version of PsiPhi and this work examines three additional models. Previous incompressible works [2, 3] on this setup emulated the effect of acoustic oscillations by introducing sinusoidal pulsations at the inlet with a frequency of 50Hz. We apply the same technique for the simulations and match the results with those from the modified compressible version, albeit for a compact domain which cannot be expected to capture the lowest acoustic frequencies. Apart from assessing performance, we also make comparisons of the simulation cost and stability to gain a better perspective of whether new FSD models and the compressible description are favorable.