Master thesis and internship[BR]- Master's thesis : Numerical study of boundary layer stability and compressible flow phenomena in a high-speed low pressure turbine with elevated free-stream turbulence[BR]- Internship

Abstract

This work aims to study the flow through high-speed low-pressure turbines encountered under on- and off-design conditions in geared turbofans. DNS are performed on the Belgian tier-1 cluster Lucia using the numerical solver ArgoDG implementing the discontinuous Galerkin method. Mach numbers of 0.7, 0.9 and 0.95 are considered combined with a Reynolds number of 70,000. A free-stream turbulence intensity ranging between 2.8-3.0% at the blade is generated using a precursor turbulence injection method. The blade loading, the boundary layer, the wake behaviour as well as the separation and transition phenomena play key roles in flow physics. A direct comparison is performed with experimental data from the SPLEEN project and numerical data obtained with clean inlet conditions. A close match with the experimental data is observed for blade loading and wake. In the subsonic case, a long separation bubble provoked by an adverse pressure gradient is observed at 61% of the suction side (SS). The flow reattaches before the trailing edge thanks to the flow transition enhanced by free-stream turbulence. In the transonic and the choked case, the shock spanning the flow passage considerably impacts the separation located approximately at 71% of the SS. The shock generates a strong compression followed by pressure recovery which first detaches the flow prematurely before its rapid reattachment. Throughout this separation bubble, the flow remains laminar even though an onset of transition is observed. The quasi-laminar nature impacts the BL characteristics and induces a strong momentum defect. Furthermore, observed losses increase with Mach number.