Modeling Combustor Turbine Interaction Using Efficient Joint Simulation Strategy

Abstract Computational modeling of hot streak migration in gas turbines is challenging due to multi-scale physics and dynamic interaction between the combustor and the high-pressure turbine (HPT) first stage. The standard practice for modeling such interactions has been performing a 1-way transfer of boundary conditions from the combustor exit to the turbine inlet. This approach is simple but not ideal for capturing the intricate flow perturbations that travel across the components and, hence, not suitable for accurately predicting hot streak migration. An improvement on the standard practice is to conduct separate component simulations and use a 2-way boundary-condition exchange process, which we call co-simulation. In co-simulations, the information between the combustor and the HPT is exchanged in an iterative loop until convergence is achieved. The co-simulations are performed on the hot section of a Honeywell turbofan engine using Stress Blended Eddy Simulation (SBES) in the reversed flow annular combustor and Reynolds Averaged Navier Strokes (RANS) in the HPT. However, the most accurate combustor-turbine interactions are modeled using joint simulation in which the combustor and the HPT stage are in the same computational domain. Therefore, the joint simulation process excludes the need for any boundary condition exchange. The SBES turbulence model, Flamelet combustion model, and discrete phase-based spray model are applied to the entire domain. Inherent to joint simulations, the transient HPT calculations require the time scale to be that of HPT, which is generally one order of magnitude lower than the combustor time-scale. As a result, joint simulations are computationally very costly (in most situations, prohibitive) compared to co-simulations. In this paper, the computational viability of joint simulations, as a better alternative to co-simulations, is explored using a mixing-plane interface in the HPT. Such an approach ameliorates the disparity in time-scale between the combustor and rotor, which is observed in calculations of joint simulations. As the calculations in joint simulations are performed at combustor time-scale, the overall process hence becomes computationally faster than co-simulations. The hot streak migration in the HPT is modeled by using a separate simulation of the HPT with sliding mesh (advanced at rotor time-scale). The aero-thermal flow solution and hot-streak migration in the HPT stage are compared between the 1-way transfer, co-simulation, and joint simulation. The distribution of near-wall blade temperatures (instantaneous, period-averaged, maximum, and minimum) is analyzed.