The Development of Turbulence Quantities in Different Intermediate Turbine Duct Configurations

The experimental investigation examined the influence of high turbulence intensity, large scales, and turbulence anisotropy on turbulence decay within the intermediate turbine duct (ITD). The paper focuses on two different test configurations of the intermediate turbine duct, which is an annular s-shaped channel used in turbofan engines to guide the flow from the high-pressure turbine (HPT) at a smaller radius to the low-pressure turbine (LPT) at a higher radius. Two state-of-the-art intermediate turbine duct concepts are in focus. The most common duct is the turbine center frame (TCF), featuring non-turning struts. The exit-to-inlet area ratio of the TCF is higher than one, leading to a flow deceleration through the duct.—On the other hand, the turbine vane frame (TVF), also known as integrated concept, can be considered as a direct evolution of the diffusive duct. The integrated concept involves integrating the function of the LP turbine’s first vane row into the duct by introducing turning struts and splitters. However, the turning struts and splitters cause an acceleration in the tangential flow direction while deceleration in the meridional direction occurs. The overall Mach number increases from the inlet to the exit within the component. The present study obtained hot-wire anemometry measurements using a triaxial and a single hot-film probe. The experiments were conducted in a two-stage, two-spool transonic turbine test rig at the Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology, which includes relevant purge and turbine rotor tip leakage flows. The two test setups include the same (HPT) stage, different intermediate turbine ducts, and a low-pressure vane or blade row, respectively. Several methodologies were used to process the data and to obtain the autocorrelation function, integral length scale, and turbulence kinetic energy dissipation rate. The turbulence quantities at the inlet to the ducts show the same characteristics in both configurations. The acquired measurement data illustrates different turbulent mixing within the intermediate turbine duct. Moreover, the high turbulence quantities at the exit of the TCF duct dominated the shroud region. In contrast, the flow field at the TVF exit is dominated by TVF secondary flow and vane wakes. These results acquired under engine realistic rig flow conditions enable a deeper understanding of the relationship between loss and turbulence quantities for different intermediate turbine duct configurations.