The aim of the present paper is to analyze and discuss in detail the effects of the upstream incoming wakes on both the aerodynamic loading and the evolution of the laminar separation bubble developing along the suction side of the high-lift T106-C low pressure turbine blade at engine similar Reynolds and Mach numbers, but at a low free stream turbulence level. The investigation is carried out numerically by means of steady and unsteady RANS simulations for two different Reynolds numbers (100,000 and 140,000), employing the SST turbulence model coupled to the γ–Re~θt transition model. The numerical results are compared with the experimental data provided by the von Karman Institute in terms of variation of losses and blade loading between steady and unsteady inflow conditions. In general, the incoming wakes have a crucial effect both on the reduction of the separation bubble and on the modification of the blade loading. This is analyzed in detail, in order to separate these contributions.

The scope of this work is to obtain a deep insight of the occurrence, development and evolution of the laminar separation bubble which occurs on the suction side of the high-lift T106-C low pressure turbine blade operated at correct engine Mach and Reynolds numbers. The commercial codes Numeca FINE/Turbo and FINE/Open were used for the numerical investigation of a set of three different Reynolds numbers. Two different CFD approaches, characterized by a progressively increasing level of complexity and detail in the solution, have been employed, starting from a steady state RANS analysis and ending with a Large Eddy Simulation. Particular attention was paid to the study of the open separation occurring at the lowest Reynolds number, for which a Large Eddy Simulation was performed in order to try to correctly capture the involved phenomena and their characteristic frequencies. In addition, the potentialities of the codes employed for the analysis have been assessed.

The scope of this work is to perform a single-objective optimization of the high-lift and aft-loaded T2 low pressure turbine blade profile previously designed at the von Karman Institute for Fluid Dynamics (VKI). At correct engine Mach and Reynolds numbers and for a uniform inflow at low turbulence level, a laminar separation bubble occurs in the decelerating part of the suction side. The main goal of the optimization is to obtain a high-lift and aft-loaded blade characterized by lower aerodynamic losses with respect to the original profile. The optimization uses a metamodel-assisted Differential Evolution algorithm, with an Ordinary Kriging metamodel performing the low-fidelity evaluations and Numeca FINE/Turbo for the high-fidelity ones. The numerical results relative to the optimized profile are compared with those obtained for the baseline profile, in order to highlight the improvements on the blade aerodynamic performance coming from the optimization process.

The aerodynamic performance of a high-load low-pressure turbine blade cascade has been analyzed for three different distributed surface roughness levels (Ra) for steady and unsteady inflows. Results from CFD simulations and experiments are presented for two different Reynolds numbers (300000 and 70000 representative of take-off and cruise conditions, respectively) in order to evaluate the roughness effects for two typical operating conditions. Computational fluid dynamics has been used to support and interpret experimental results, analyzing in detail the flow field on the blade surface and evaluating the non-dimensional local roughness parameters, further contributing to understand how and where roughness have some influence on the aerodynamic performance of the blade. The total pressure distributions in the wake region have been measured by means of a five-hole miniaturized pressure probe for the different flow conditions, allowing the evaluation of profile losses and of their dependence on the surface finish, as well as a direct comparison with the simulations. Results reported in the paper clearly highlight that only at the highest Reynolds number tested (Re=300000) surface roughness have some influence on the blade performance, both for steady and unsteady incoming flows. In this flow condition profile losses grow as the surface roughness increases, while no appreciable variations have been found at the lowest Reynolds number. The boundary layer evolution and the wake structure have shown that this trend is due to a thickening of the suction side boundary layer associated to an anticipation of transition process. On the other side, no effects have been observed on the pressure side boundary layer