Experimental investigation of the flow field in an aggressive intermediate turbine duct

Doctoral thesis, 2009

Intermediate turbine ducts are used for connecting the high-pressure turbine to the low-pressure turbine in turbofan engines. In order to meet the demands for more efficient and environmentally friendly jet engines, future intermediate turbine ducts need to have larger radial off-sets without increasing their length. In addition, reducing the length of the intermediate turbine duct reduces the weight of the engine. This thesis describes a detailed measurement campaign of an aggressive intermediate turbine duct. Its length was about 20% shorter than conventional engines with similar characteristics; hence the word aggressive. The first part of the thesis reports briefly the design and construction of the large-scale, low-speed turbine facility that was a part of this project. The turbine stage provided proper inlet boundary conditions for the downstream intermediate turbine duct. The second part of this thesis discusses the results from measurements, including endwall flow visualization, endwall static pressure measurements, 5-hole pressure probe measurements and time-resolved and phase-resolved two-component hot-wire measurements. The measurements are expected to provide a useful database for validation of computational tools, especially since they contain detailed information about both the average flow and the turbulence. From the measurements no endwall flow separation due to the shortening of the duct could be detected. It was also found that the break up of the tip leakage flow formed a pair of counter-clockwise rotating vortices for each turbine vane sector. The phase-resolved measurements indicated that these were the wing tip vortices from the rotor blade that became stationary as the flow proceeded downstream. The phase-resolved measurements together with spectral analysis revealed that immediately downstream the turbine the flow was highly unsteady. But by the time the flow reached the low-pressure turbine vanes unsteady effects had been reduced and the flow was dominated by stationary structures.