The Effect of Reynolds Number on the Flow Around the T106C Very High Lift Low PressureTurbine Linear Cascade

Authors

Antoine Dufau  - Safran Aircraft Engines, France
Julien Marty - ONERA The French Aerospace Lab, France
Estelle Piot - ONERA The French Aerospace Lab, France
Daniel Man - Safran Aircraft Engines, France

Abstract

The low-pressure turbine of turbofan engines can operate at a low Reynolds number especially at cruise condition. Consequently, the boundary layer over airfoils can be laminar on a large part of the suction side. As the low-pressure turbine is responsible for 30% of the engine weight, a common engine design tendency is the reduction of turbine stage number, which leads to an increase of the blade loading. The main consequence is the presence of a high adverse pressure gradient over suction side leading to the separation of the laminar boundary layer. The evolution of the separated shear layer is then closely linked to the laminar-turbulent transition. Moreover, the Reynolds number influences the topology of the laminar separation bubble. Indeed, at a really low Reynolds number, the separation bubble can be open, which means that there is no reattachment of the separated shear layer. When the Reynolds number is higher, the separation bubble may be closed, so the separated shear layer reattaches before the trailing edge. This closed bubble is categorized as long or short depending on the static pressure plateau length and the generated losses. The switch from short bubble to long bubble is called the bursting. This paper aims at investigating this phenomenon by performing direct numerical simulations of the flow around T106C turbine cascade blade for different Reynolds numbers. The freestream turbulence of the wind tunnel is replicated by adding an injection of synthetic turbulence at the inlet plane with the Synthetic Eddy Method. This method is extended to periodical flows because of the periodicity of the 2.5D configuration in both pitch-wise and span-wise directions. The range of simulated Reynolds numbers leads to the observation of both long and short laminar separation bubbles. Thus, the effect of Reynolds number on the flow and the boundary layer behavior is described. Moreover, DNS results are compared to experimental data in order to investigate discrepancies already observed at the Reynolds numbers 80,000 and 100,000.