Colin Heye

Flame stability analysis in an ultra compact combustor using large-eddy simulation

Large eddy simulation (LES) of an experimental ultra-compact combustor (UCC) was performed in order to investigate the mechanisms of flame stability in the presence of liquid fuel. The experimental setup was designed to isolate the effects of centrifugal forces on fuel mixing and combustion efficiency. The LES solver was implemented in the open source software OpenFOAM, including evaporation coupling and a flamelet-progress variable approach (FPVA) tabulated combustion model. This work serves as a continuation of previous work on validation of inert flow in this configuration. Simulations indicate that flame stabilization occurs through low velocity, high temperature regions formed in the toroidal portion of the configuration. The high enthalpy in this region interacts with the incoming spray droplets leading to evaporation and subsequent ignition. It was also found that the initial ignition and stabilization of the flame occurs over long time scales comparable to the time taken to traverse the circular region of the geometry. Comparison with experimental data show reasonable agreement, indicating that the stabilizaton mechanism found in the simulations is valid.

Large Eddy Simulation Analysis of Flow Field Inside a High-g Combustor

Inter-turbine burners are useful devices for increasing engine power. To enable inter-turbine burners for aviation applications the size of combustion devices needs to be reduced. High-g ultra-compact combustors (UCC) are a technology for reducing the size of combustors. In these combustors the fuel and air are swirled around the centerline at velocities large enough to impact centrifugal forces. In this work, the large eddy simulation (LES) method is used to understand mixing and flow dynamics inside centrifugal-based combustion systems. Simulation results show that mixing of fuel and oxidizer is based on a jet-in-crossflow system, with the fuel jet issuing into a circulating oxidizer flow stream. The momentum ratio between the jet and the crossflow determine fuel penetration, and will determine combustion eciency. Simulation results exhibit significant entrainment of fuel into recirculation zones inside the combustor, however more extensive experimental data is required to validate this result. ⇢ Filtered density ej Filtered velocity f ˙ W Filtered evaporation source term ˜ P Filtered pressure ⌧ij Viscous stress tensor Tij Sub filter stresses F Drag force

Analysis of Multiple Scalar Large-Eddy Simulation/Probability Density Function Formulation for Turbulent Spray Combsustion

A large eddy simulation (LES)/probability density function (PDF) method is proposed for modeling turbulent spray combustion. The PDF method has the advantage that the chemical source term appears closed but requires models for the small scale mixing process. The transport equation for the joint-scalar PDF is high dimensional and solved using a Lagrangian technique. A stable and consistent numerical algorithm for the LES/PDF approach is presented. An evaporating spray experiment is used to verify the numerical implementation. To understand the modeling issues in the PDF method, direct numerical simulation of a spray ame and an equivalent gaseous ame are carried out. It is demonstrated that currently used models for the scalar time scale are reasonably accurate in the spray ame.

A Comparative Study of the Simulation of Turbulent Ethanol Spray Flames

Experimental data for a series of spray flames is utilized to perform analysis of validation studies conducted by multiple contributors. In this multiphase context, various choices for boundary conditions as well as modeling frameworks and formulations are evaluated. Both large eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) approaches showed the ability to capture droplet evolution with regards to mean and fluctuating velocities. This accuracy is contingent on the proper specification of both droplet and gas phase velocities at the jet exit. The combined effect of combustion and evaporation model choices impacts the downstream volume flux of droplets and resulting gas phase temperature. Further investigation is required to isolate individual model effects for high-temperature spray-laden environments. Proposed solutions involve the simulation of a wider array of flow conditions or lowerlevel experiments to remove the effects of model coupling.