Impact of Unsteady Wakes on the Secondary Flows in a High-Speed Low-Pressure Turbine Cascade

Authors

Gustavo Lopes  - von Karman Institute for Fluid Dynamics, Belgium
Loris Simonassi - von Karman Institute for Fluid Dynamics, Belgium
Sergio Lavagnoli - von Karman Institute for Fluid Dynamics, Belgium

Abstract

The geared turbofan is regarded as a key architecture to fulfil the target reduction in CO2, N Ox and noise footprint imposed by flight initiatives due mid 2030s. The gearbox that is introduced in this concept enables the low-pressure turbine (LPT) to operate at higher rotational velocities. Consequently, the flow conditions in the LPT are characterized by low Reynolds number, encountered during cruising, and transonic Mach numbers, resultant from the increase in low-pressure spool rotational velocity. Current efforts in exploring the design space of high-speed LPTs are being done in the scope of the EU SPLEEN project that aims at accelerating the development of tools to design high-performance and efficient modules. In a previous two-part work, the on- and off-design characterization of a novel open access transonic linear cascade was presented. The latter was presented without the presence of incoming wakes served as a baseline case for the pathway of data to disseminate in the scope of the project. However, it is well known that the current design of turbomachinery components must account for engine-relevant conditions. The typical unsteady wakes encountered in a LPT environment are one of the main mechanisms impacting the transition process in the suction side boundary layer. Modern LPT profiles are designed to account for the wake induced benefit of triggering the transition of the boundary layer on the separated shear layer, hence reducing the losses in the time-averaged frame. On the other hand, the wakes also impact the flow field down to the secondary flow region. In the current work, the impact of unsteady recreated wakes is measured in a transonic linear cascade. The outlet Mach and Reynolds are engine-representative. On top of that, the reduced frequency and flow coefficient also approximate engine-relevant values. The impact of the wakes is characterized all the way from the cascade inlet to the cascade outlet where the cascade performance is characterized in terms of flow deviation and losses. This work aims at characterizing the combined interaction between unsteady wakes, secondary flows and blade aerodynamics.