Abstract
The integration design of the intermediate turbine ducts (ITDs) with the first row of the low-pressure turbine vane can significantly reduce the length of the turbine section, thus reducing the weight and drag of the aero-engine. This paper investigates the effects of the hub profile on the aerodynamic performance of integrated ITDs (IITDs). The flow features and loss mechanism of four IITDs are studied by experimental, numerical, and theoretical methods. In the baseline case, an open corner separation occurs near the hub-suction surface corner, which results in a significant loss. The loss is broken down into the parts generated by the mean vortex and turbulence theoretically. The open corner separation causes significant turbulence loss. To reduce the size of the separation zone, the positive radial/spanwise pressure gradient near hub is increased by moving the hub profile near the vane rear part slightly downward. As a result, a small closed corner separation with three-dimensional topology occurs instead of the open corner separation in the baseline case. The corner shape factor is defined to quantitatively describe the closed corner separation. When the hub profile moves further downward, the loss due to the corner separation reduces, but the loss generated in the vane passage away from hub increases mainly due to the mixing as the low-momentum flow near the hub transports toward the mid span. The change of the overall loss is subject to the combination of the two effects, and should be balanced during the design process.
