Numerical Study of Combustor-Turbine Interaction by Using Hybrid RANS-LES Approach

Abstract

The complex flow field of gas turbine lean combustors is meant to reduce NOx emissions and maintain a stable flame by controlling the local temperature and promoting high turbulent mixing. Still, this may produce large flow and temperature unsteady distortions capable of disrupting the aerodynamics and heat transfer of the first high-pressure-turbine cooled nozzle. Therefore, the interaction between the combustion chamber and the turbine nozzle is analyzed first with the help of scale-resolving simulations that notably also include a realistic turbine nozzle cooling system. To determine the nature and severity of the interaction, and the risks associated to performing decoupled simulation, the results of the coupled computer simulation are analyzed and compared with those of decoupled simulations. In this case, the combustor is computed by replacing the turbine nozzle with a discharge convergent with the same throat area, and the conditions at the interface plane are used as inlet boundary conditions for a conventional RANS of the nozzle. The analyses of the coupled and decoupled simulation reveal that the combustion chamber is weakly affected by the presence of the nozzle, whereas the two thermal fields of the nozzle surface differ considerably, as well as the disruption of the film cooling by the incoming flow distortions.

Unsteady Flows and Component Interaction in Turbomachinery

“…The swirling flow was also responsible for the redistribution of the cold streak downstream of the vane, with a specific pattern associated with the clocking between the residual swirl and the vanes. Film cooling effectiveness was also analyzed by [82] through RANS simulations, which were not able to correctly simulate coolant traces due to the high mixing associated with the presence of the swirl, coherently with what was found by Cubeda et al [83]. However, RANS was able to qualitatively evaluate heat transfer coefficient maps if compared with the available experimental data.…”

“…The relevance of inlet conditions to accurately perform combustor/turbine simulation and the superior performance of an integrated approach were also demonstrated by [208]. A recent work by Tomasello et al [82] confirmed that an integrated approach based on high-fidelity turbulence was recommendable for the accurate prediction of the heat transfer in cooled high-pressure vanes. Similar results were shown by Thomas et al [209], where statistics of the unsteady heat load on an uncooled high-pressure vane were analyzed using LES, also underlining the importance of clocking position between the combustor and the vane.…”

Study of Combustor–Turbine Interactions by Performing Coupled and Decoupled Hybrid RANS-LES Simulations under Representative Engine-like Conditions

“…Looking at the time-averaged field, an evident blockage effect can be noted due to the presence of the leading edge (LE) of the following first-stage stator. As a matter of fact, according to [38,39], the presence of the LE results in a strong deceleration in this region, that can be clearly observed in the central portion of the plane 39.5. This is clearly compensated for by a non-negligible acceleration around the LE.…”

“…More recently, Tomasello et al [38] used the SBES approach to simulate a fully integrated combustor-nozzle configuration under realistic operating conditions, equipped with a realistic turbine nozzle cooling system. The results were then compared to results obtained previously by performing an RANS, as per the standard design.…”

“…As a matter of fact, even if the turbulent length scale values and distributions were comparable for the two simulations at the interface plane between the components, it was proven that the higher turbulent dissipation rate that characterized the RANS simulation ensured that the turbulent length scale decayed faster in the RANS case. Moreover, in order to fully study the impact of the presence of the combustor, a further numerical analysis was carried out by performing an SBES of the isolated NGV [39]. To achieve this, two-dimensional unsteady boundary conditions were prescribed at the inlet of the NGV, that were previously extracted from a high-fidelity available SBES simulation of the stand-alone combustor at runtime.…”