THE EFFECTS OF CASING PROFILE ON THE AERODYNAMICS OF INTEGRATED INTERMEDIATE TURBINE DUCTS

To reduce the engine's length and weight, the concept of integrated intermediate turbine duct (IITD) is proposed, in which the first row of the low-pressure turbine vanes are replaced by the turning struts in ITD. The effects of the casing profile on the flow features and loss mechanism in the IITD are investigated by experimental, numerical and theoretical methods. In the baseline case, the casing passage vortex at the exit of the IITD is featured with two branches, which is caused by the entrainment effect of the suction side leg of horseshoe vortex near casing. By making the casing profile upstream of the leading edge more downward convex, the thickness of the casing boundary layer can be reduced, and the horseshoe vortex is weakened. The structure of the exit casing secondary flow is thus more complete. In the IITD with higher mean rise angle, the entrainment effect has the ability to reduce the low-momentum fluid and suppress the separation on the suction surface. A method of controlling the casing secondary flow is proposed accordingly. To analyze the loss mechanism, the loss is broken down into the parts generated by mean vortex and turbulence theoretically. The casing boundary layer acceleration can lead to larger velocity gradient and loss caused by mean vortex. While the turbulent dissipation will be reduced on the other hand. Large turbulent dissipation can also be generated when the mixing between the casing secondary flow and wake is enhanced.