Turboprop turbines: aero modeling and performance analysis

The aviation sector has reached an extremely high level and development has an almost asymptotic trend. To make this possible, simulations are carried out to provide more details of the physical knowledge about flows, bringing to the design engineers additional awareness about aerodynamic phenomena. It is of fundamental importance to have processes and software that allow you to predict performance in the best possible way during the design and analysis phases. This will lead to savings in development time and costs and performance improvement. The main objective of this thesis is to create a set of models, from one-dimensional to full 3D, of the turbines of an existing turboprop engine using more recent methodologies in a sort of reverse engineering. Small turboprop engine has various types of missions and multiple and widely spread operative points. For this reason, a flexible model is fundamental from the designer point of view in order to quickly evaluate performances in different off-design conditions and component robustness. Initially, a simple “flowpath-only” model has been created, considering the main flow working in an ideal streamtube, neglecting any interaction with a real turbine mechanical arrangement. This ideal condition has been modeled in a 1D simplified setup and in a more complex 3D CFD environment. Subsequently, the models have been refined inserting in the simulation the main interaction effects of the secondary air system on the main flow. Once model are available, it is possible to leverage on them in order to access performance derivatives to main design parameters. One of the most impacting parameters on turbines performances is the Rotor Tip Clearance (RTC). Unfortunately, RTC are usually associated with an high level of uncertainties, since is very difficult to quantify them in real operative condition and, in any case, they will widely vary during engine mission and lifespan. For this reasons, it is particularly important to characterize turbine performances as function of RTC. The mono and three-dimensional turbine models built in the first part of this thesis will be used in the second part to perform the above mentioned study of RTC. In particular, obtained results will be presented highlighting main effects of the interaction between main and bypass flows, while varying RTC gaps. Different RTC mechanical arrangements and modeling will be presented and compared.