Large Eddy Simulation Of Realistic Annular Gas Turbine Combustor

A large eddy simulation approach for the modeling of combusting flow with spray in realistic gas turbine combustors is proposed in this paper. The flow solver solves compressible Navier-Stokes equations to capture acoustic waves and combustion induced flame instabilities. Unstructured mesh is adopted to deal with the complex geometry of realistic combustors. Numerical schemes of second order both in space and in time are used to speed up simulations and enhance numerical stabilities. Simulation parallelization is achieved by adopting the technique of Message Passing Interface (MPI). A one equation dynamic subgrid model, which solves a transport equation of subgrid kinetic energy and also provides a subgrid velocity scale for the two-way coupling of two-phase spray flows, is used to model the effect of the subgrid scales on the resolved large scales. Subgrid combustion is modeled by an extended eddy dissipation model. An Eulerian-Lagrangian approach is used to model the two-phase spray flow, and spray particles are tracked by a two-way coupling Lagrangian approach in which spray secondary breakup and vaporization are included.The proposed approach is then applied to simulate the combusting spray flow of a realistic multi-burner annular combustor. The computational domain has an inflow boundary taken at the upstream compressor exit and an outflow boundary located at the inlet of the downstream turbine. A wave transmittable convective outflow boundary condition is applied at the outlet boundary. The computational domain is taken as a single sector composed of a diffuser, a swirler, two rows of primary and secondary air intake holes and cooling air films.The objectives of this study are to demonstrate the capability of the proposed approach to investigate the complicated flow and combustion dynamics in a realistic combustor. The predicted instantaneous and time averaged fields of velocity, temperature, pressure, fuel and oxygen concentrations were investigated. The vortex structures and flame instabilities were also studied using computed vorticities and spectrum analysis. The predicted results nicely reproduced the flow, spray and combustion dynamics and successfully captured the main features of the studied combustor such as the precessing vortex core (PVC) and combustion-induced flame instability. The current study reveals that there two dominant frequencies of pressure fluctuations inside the inner chamber. One dominant frequency is related to the precessing vortex core and pronounced immediately downstream the swirler and gradually disappears due to the destruction by the downstream turbulence. The other dominant frequency is caused by the flame induced instability and prevails inside the whole region of the inner chamber. The -5/3 law of different locations three velocity components energy spectrum characterizing the inertial sub-range is largely satisfied. Finally, the predicted exit temperature were also compared with experimental data and good agreements were obtained.