Advancements in Automated Methods for Fluid-Dynamic Turbomachinery Design

• Main Author: Agromayor Otero, Roberto
• Format: Dissertation
• Language: English

Automated design methods are emerging as a powerful tool for the fluid-dynamic design of turbomachinery components. Such automated methods integrate mathematical models of different level of sophistication with numerical optimization techniques to explore large design spaces in a systematic way. This, in turn, allows the designer to achieve higher performance gains and shorten the development time with respect to traditional design workflows based on trial-and-error. In this context, the present thesis proposes a collection of models and methods for the preliminary and aerodynamic design optimization of turbomachinery that addresses some of the limitations of the design methods currently in use. With regards to the preliminary design phase, this work proposes a design optimization method for axial turbines with any number of stages. The method is based on a new mean-line model that accepts arbitrary equations of state to evaluate the thermodynamic properties of the fluid and empirical loss models to estimate the entropy generation. In addition, the kinetic energy recovered at the exit of the last stage is predicted using a new one-dimensional annular diffuser model based on the balance equations for mass, momentum, and energy. In contrast with existing methods, the preliminary design problem was formulated as a constrained optimization problem and solved using a gradient-based algorithm. This choice of optimization method allows the designer to: (1) integrate the turbine, diffuser, and loss models in a simple way by means of equality-constraints and (2) _nd the optimal solution of multi-stage design problems with tens of design variables at a low computational cost. The preliminary design method was applied to a case study and a sensitivity analysis revealed that there exists a locus of maximum efficiency in the specific speed and diameter plane (i.e, the Baljé diagram) that can be predicted with a simple analytical expression. Concerning the aerodynamic design phase, the present work proposes a unified geometry parametrization method based on computer-aided design (CAD) for axial, radial and mixed-ow turbomachinery blades. The method uses conventional engineering parameters (e.g., chord, metal angles, thickness distribution) and it exploits the mathematical properties of non-uniform rational basis spline (NURBS) curves and surfaces to produce blades with continuous curvature and rate of change of curvature. In addition, the method provides the sensitivity