Flows in an intermediate turbine duct (ITD) connecting high-pressure turbines (HPT) and low-pressure turbines (LPT) are highly complex, influenced by the upstream HP turbine flow structures. Non-uniformities originating from the duct with struts of different sizes also affect the LPT inflow conditions, resulting in reduced efficiency. The goal of this paper is to provide detailed understanding of the flow physics and loss mechanisms within the ITDs for highly efficient ITD designs. Steady and unsteady numerical simulations of flows through the ITDs in the presence of HP blade and LP vane were conducted. Effects of upstream HP blade on flow fields and loss characteristics within the ITDs are explored. The generation and propagation of wake and secondary flows through the whole configuration is described, including the fast Fourier transformation (FFT) analyses of the flow in the ITD. Results from the numerical simulations show complex flow patterns resulted from blade-strut-vane flow interactions in a high-endwall-angle duct, which are not obtainable from ITD-only simulations. Moreover, the ITD has a strong amplifying effect on the distorted inflow, and the inflow with the upstream wake and secondary flows introduces a high loss area along the casing at ITD exit. Detailed results are presented and discussed for the flow physics and loss mechanisms within the ITD.

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