Nonlinear Harmonic Method Applied to Turbine Conjugate Heat Transfer Analysis for Efficient Simulation of Hot Streak Clocking and Unsteady Heat Transfer

High pressure turbine (HPT) optimum thermal design is critical in further improving gas turbine efficiency. However, this is a challenging task as it requires accurate simulation of unsteady flows in conjunction with heat transfer simulation of the airfoil solid structure, which in turn requires large computational resources. In this work, the nonlinear harmonic (NLH) method is applied to conjugate heat transfer (CHT) simulation to provide an effective tool for turbine thermal design and analysis. The NLH method can be seen as a computationally affordable alternative to the traditional time-marching unsteady simulation particularly in turbomachinery applications, where the unsteadiness is mostly periodic. When applied to CHT simulations, it also addresses the difficulty of dealing with large time-scale mismatch between fluid and solid domains by casting the periodic perturbations into the frequency domain. Furthermore, it naturally allows for the study of hot streaks clocking effects by means of space harmonics. These capabilities are demonstrated on the HPT of the NASA/GE Energy Efficient Engine (E3), where hot streaks clocking effect on the metal temperature of the nozzle guide vane (NGV) is simulated. Also, the time variation of the rotor blade metal temperature as it crosses the hot streaks is simulated. The results confirm that, with only a single NLH solution, different aspects of the thermal design of a multi-stage turbine can be explored with little additional computational effort with respect to the standard steady approach.