Steady and unsteady CFD calculation of the laminar-to-turbulent transition in a turning mid turbine frame with embedded design

In order to meet the weight requirements of future jet engines S-shaped intermediate turbine ducts can be supplied with turning load carrying struts in order to save the first vane row of the subsequent low pressure rotor. In such a duct large flow structures emanating from the outlet of the transonic high pressure stage are transported towards the low pressure rotor and are superimposed by secondary effects generated by the turning struts within the duct. To reduce the fluctuations behind the S-shaped duct and to homogenize the flow, the duct can be equipped with additional splitters. Such an embedded design has the advantage of a more homogenized flow entering the low pressure rotor, thus improving efficiency. It is crucial for the overall efficiency to optimize the design of such an intermediate turbine duct. To understand all flow effects it is helpful to perform CFD calculations which do not neglect laminar-to-turbulent transition. Therefore this paper presents steady and unsteady CFD results of an S-shaped turbine duct with splitters considering boundary layer transition using Menter's γ-ReΘ model. The differences between steady and unsteady simulation and the influence of transition are discussed.