Development of a Parametric 3D Turbomachinery Blade Modeler

Abstract

Nowadays Organic Rankine Cycle (ORC) power systems are of paramount importance to exploit waste heat and renewable energy sources. Standard design rules and empirical models are mostly available for steam/gas turbines and can not be directly applied for ORC. Because of this, a redefinition of the design strategy is needed, starting from the turbine concept, passing through dedicated preliminary design optimization and eventually arriving at a complete new redefinition of the optimal blade profiles through advanced optimization methodologies. To fill the gap between (zero-dimensional) mean-line analysis and 3D fluid-dynamic analysis a Turbomachinery Blade Modeler (TBM) is required. The modeler not only gives direct control of the blade geometry but also provides valuable feedback of the design. This allows the user to construct a good initial design before refining it with more computationally expensive methods. The TBM is developed using the python API within the framework of the open source software FreeCAD. Furthermore, it is also tightly coupled to two mesh generators, an in-house one UMG (Unstructured Mesh Generator) and to the open source Salome. This link guarantees the quasi-automatic generation of high quality CFD meshes for any kind of blade design. The approach to construct a variety of turbomachinery blades is based partially on state-of- art parametrization techniques and uses fundamental design variables such as metal blade angles, chord length and the stagger angle. The geometry is purely build up with NURBS curves and surfaces which has the benefit that sharp edges are avoided and high smoothness of the profile shape is guaranteed. NURBS include control point position, weight and curve degree which allow a flexible control of the shape without introducing many variables, which is beneficial in optimization routines. The TBM allows for the design of any kind of blade: these include axial, centrifugal, centripetal, radial rotors/ impellers and mixed blades. Moreover, to aid the designer the flow passage area distribution can be visualized run time. The TBM has been already successfully tested for the design of a high loaded centrifugal rotor. Additionally, a complex twisted and flared axial compressor, the NASA Rotor 67 was reconstructed using the TBM. The small differences between the reference geometry and the reconstructed one were evaluated with 2D CFD simulations. Finally, a design of a radial-inflow turbine was reproduced and meshed for future analysis. The parametric 3D turbomachinery blade modeler has proven to be a very powerful tool for designing turbine and compressor stator/rotors. Moreover, after the consolidation of the algorithms and a direct coupling with the CFD solver SU2, the tool will be ready to be used as a turbomachinery optimization environment.