Embedded Large Eddy Simulation for High Pressure Turbine Tip Clearance Analysis

This research proposes to study the effect of tip gap leakage flow in a High Pressure Turbine by means of a high resolution Embedded Large Eddy Simulation. URANS simulations of turbomachinery flows fail to accurately represent the vortical structures seen in experimental studies. These vortical structures affect the flow separation from the walls of the inter-turbine duct in multi-stage turbines. This study will use embedded large eddy simulation to capture these vortical structures. Preliminary work has shown that modeling of the full turbine annulus is computationally intractable. A single passage model has been developed to enable the time-efficient simulation of the system. This involved modification to the turbine nozzle to create a one-to-one periodicity with the rotor, allowing for a periodic domain. This modified geometry was analyzed using the unsteady RANS equations with the k-omega SST turbulence model with a sliding mesh to account for the relative motion of the rotor to the rest of the system. This URANS solution was used as an initial condition and reference point for the ELES solution. Turbulent statistics were gathered for each of these solutions. Both solutions compare favorably to the harmonic balance model used in the design of the original geometry. Significant differences in the vortical structures passing through the tip gap region generated by these unsteady simulations are found. These highly-resolved structures will be used in later studies to examine the separation of flows in the inter-turbine duct.