Unsteady Numerical Simulations of a Diffusive High – Pressure Turbine Stage

Rotating Detonating Engines (RDE) could provide performance improvements in the Gas Turbine thermal cycles. Since RDE uses detonative combustion, the outflow temperature and pressure are much higher than in traditional combustors and are highly unsteady. The harsh conditions represent a challenge for the turbine integration, with a high Mach number at the inlet of the turbine. In previous work, the CT3 HPT vane and endwalls were optimized to take in an averaged 0.6 Mach number. The diffusive endwalls and the elevated inlet Mach number require careful attention to the secondary flows generated in the vane, and its interaction with the stage’s rotor. The secondary flows vortex structures highly impact the turbine’s efficiency, and the passage vortex has a dominant effect. The objective of this work is to analyze and compare the optimized turbine stage with the CT3 HPT at these harsh (but stationary) inlet conditions, also assessing the secondary flows the different configurations produce, by solving the Unsteady Reynolds Averaged Navier-Stokes equations (URANS) with the commercial solver Ansys CFX. As a preliminary analysis, steady state (RANS) simulations were done, using a mixing plane between the blade rows. The steady analysis was used to start the unsteady simulations, and to evaluate and compare the stator’s vortex structures. The URANS analysis is done using the Time Transformation method, capable of addressing the unequal pitch in the blade rows and recognizing the periodicity of the flow, without requiring computing a significant portion of the wheel. The post-processing allows to visualize the different configurations’ helicity and lambda2 criterion, which portray the secondary flow’s intensity, shape, and behavior. It also conveys the difference in blade load and efficiency.