Analysis of a LPT Rotor Blade For a Geared Engine. Part I: Aero-Mechanical Design and Validation.

The rotational speed of low pressure turbines (LPT) for geared turbofan applications is significantly increased looking for potential benefit in performance, weight and overall dimensions. As a drawback, the high speed LPT are characterized by critical mechanical constraints due to the large centrifugal stresses in conjunction with the use of lightweight materials. The present activity was carried out in the framework of the Clean Sky European research project ITURB (“Optimal High-Lift Turbine Blade Aero-Mechanical Design”), aimed at designing and validating a turbine blade for a geared open rotor engine. This two-part paper presents the redesign and the analysis of an optimized rotor blade starting from a baseline configuration, representative of a state-of-the-art LPT rotor. In the redesign activity high standard of performance were required in conjunction with tight mechanical and geometrical constraints. The design strategy was based on an effective multi-objective optimization strategy. The aerodynamic performance were evaluated by means of 3D steady multi-row viscous computations using a two-equation k-w turbulence model. At the same time, the mechanical integrity checks were mainly based on the evaluation of the maximum rotor tensile stress due to centrifugal forces. A simplified and very fast tool was developed in order to compute the centrifugal stress. Finally a response-surface approach based on neural-networks (ANNs) was adopted for the design space exploration. The design was validated by means of a comprehensive experimental campaign carried out in a low-speed turbine single-stage facility. A comparison between the numerical and experimental results are presented in terms of the main rotor performance for a fixed Reynolds number while varying the rotor incidence angle. Unsteady numerical analysis of both the baseline and the optimized blade were carried out by using a multi-equation, transition-sensitive, turbulence model and considering the boundary conditions measured on the test rig.