The need for high-speed low-pressure turbine modules to be used with innovative aircraft engine concept establishes critical mechanical constraints with very high hub stresses for the rotor blades, thus representing a real challenge for the design. In order to assist the designer with reliable tools it is mandatory to assess the performance of turbine rotor blades of innovative concept with both numerical and experimental investigations.
Starting from a baseline configuration, representative of the state-of-the-art of LPT high-lift rotor blades, an aerodynamic optimization was performed exploiting modern optimisation techniques. These techniques are based on the coupling between fast and flexible parametric handling of the geometries, CFD computations and meta-models like Artificial Neural Networks (ANN) or Radial Basis Functions (RBF). Such an approach accomplished a multi-objective design aimed at enhancing the aerodynamic performance while meeting mechanical and geometrical constraints.
Tests were performed on both baseline and optimised rotors within a cold-flow, large-scale laboratory turbine. Tests on turbine configuration ensured the reproduction of the correct radial equilibrium effects as well as of the rotor-stator aerodynamic interaction. The Reynolds number was investigated in the range between 50000 and 300000, which represented the operative range of the LP rotor blades of the engine. The large scale of the facility allowed detailed aerodynamic investigations, and an accurate performance analysis.
The numerical and experimental frameworks allowed one to validate and verify the optimised solution and to highlight the key features of the new design with respect to the baseline. The validation of the design and optimisation procedures was accomplished with the availability of detailed experimental data obtained for the innovative rotor blade row in a realistic environment.
The increase of the engine by-pass ratios leads to high speed LPTs for which the rotational speed is significantly increased with potential benefits in performance, weight and overall dimensions. As a drawback, the designer has to face additional critical issues during the design phases, with the consequent need for the application of optimization procedures. Indeed, the high-speed low-pressure turbine modules are characterized by critical mechanical constraints due to the large hub stresses which the rotor blades are subjected to, and represent a real challenge for the design. In order to assist the designer with reliable tools it is mandatory to assess the performance of turbine rotor blades of innovative concept with both numerical and experimental investigations.
The ITURB project has been devoted to the numerical design and experimental investigation of an LPT rotor row optimized under the aero-mechanical point of view.
Starting from a baseline configuration, representative of the state-of-the-art of LPT high-speed rotor blades, a multi-objective optimization, aimed at fulfilling the mechanical and geometrical constraints without threatening the rotor aerodynamic performance, has been performed at the University of Firenze and University of Padova.
Successively, the baseline and optimized rotor rows have been also experimentally investigated in a large scale cold flow installed at the Aerodynamics and Turbomachinery Laboratory of the University of Genova. The facility has been properly upgraded to allow detailed investigations of the flow within the two rotor rows, and in particular the measurement of the rotor aerodynamic loadings. The experimental results confirmed the numerical predictions, giving the evidence that the mechanically optimized rotor is able to maintain the aerodynamic performance of the baseline rotor.
Moreover, detailed phase-locked investigations carried out downstream of the rotor allowed the understanding of the flow physics and of rotor/stator interaction.