Characterization of a Supersonic Turbine Downstream of a Rotating Detonation Combustor

Rotating detonation combustors offer theoretically a significant total pressure increase, which may result in enhanced cycle efficiency. The fluctuating exhaust of rotating detonation combustors, however, induces low supersonic flow and large flow angle fluctuations at several kHz which affects the performance of the downstream turbine. For such flows, power extraction can be achieved by either integrating a diffuser with a conventional subsonic turbine or a nozzle with a supersonic turbine. In this paper, a numerical methodology is proposed to characterize a supersonic turbine exposed to fluctuations from rotating detonation combustors without any dilution. The inlet conditions of the turbine were extracted from a three dimensional unsteady Reynolds-Averaged Navier-Stokes simulation of a nozzle attached to a rotating detonation combustor, optimized for minimum flow fluctuations and a mass-flow averaged Mach number of 2 at the nozzle outlet. In a first step, a supersonic turbine able to handle steady Mach 2 inflow was designed based on a method of characteristics solver and total pressure loss was assessed. Afterwards unsteady simulations of eight stator passages exposed to periodic oblique shocks were performed. Total pressure loss was evaluated for several oblique shock frequencies and amplitudes. The unsteady stator outlet profile was extracted and used as inlet condition for the unsteady rotor simulations. Finally, a full stage unsteady simulation was performed to characterize the flow field across the entire turbine stage. Power extraction, airfoil base pressure, and total pressure losses were were assessed, which enabled the estimation of the loss mechanisms in supersonic turbine exposed to large unsteady inlet conditions. Frequency analysis of the pressure field across the turbine rows was used to evaluate the damping of the oblique shock waves.