Improvement of Aerodynamic and Strength Characteristics of a Multi-Shaft Axial Turbine of a Turboshaft Engine

The article presents the results of solving the complex task of increasing the rotor wheel strength factor and the efficiency of the twin-shaft axial turbine of the small turboshaft engine using methods of multidisciplinary optimization. This turbine consists of a single-stage compressor turbine (CT) and a free turbine (FT). An analysis of the original variant of the turbine revealed that the strength factor of their rotor wheels are significantly lower than the necessary structural requirement. To eliminate the occurring problem at the first step the initial task of estimation the rotor wheels only on the basis of structural requirements was performed without taking into account aerodynamic processes. As a result, variants of the turbine rotor wheels were obtained to provide the structural constraints. They were used as starting points for the complex task of optimization, taking into account aerodynamic and deformation processes. The task of multi-disciplinary CT and FT optimization was solved step by step. As a first step, specific CT and FT models were built, which as a result of their optimization allowed to ensure acceptable strength factor of rotor wheel and slightly increased turbine efficiency. In the next step, a joint model of both turbines was built and tested. Its analysis showed that mutual influence of these working processes of the turbines leads to a distortion of the flow temperature distribution in the flow path, which causes a reduction of the FT blades strength criteria to an unacceptable level. Further optimization of the joint turbine model, taking into account aerodynamic and deformation processes, made it possible to increase the efficiency of both turbines by 0.4% (for each one), providing the necessary safety margins for the disks.