Full Design of a Highly Loaded and Compact Contra-Rotating Fan Using Multidisciplinary Evolutionary Optimization

Abstract

Contra-rotation enables one to produce low-weight and high-load fans suitable for high-speed propulsion systems, such as Air Turbo Rocket engines. This paper presents a Multidisciplinary Design Optimization (MDO) methodology to achieve the full-design of highly-loaded and compact contra-rotating fans. It utilizes a multi-objective optimization at every step of the design. Performances of the two-stage machine is first evaluated by a through-flow model to determine an optimal flow path configuration. A novel parameterization based on span-wise distributions is used to smooth the transition between the preliminary design phase and the detailed three-dimensional shape optimization. High-fidelity aero-mechanical performances are then considered to generate the detailed design of the rotors, including the section profiles along the span, as well as lean and sweep. The multi-objective optimization algorithm treats simultaneously Computational Fluid Dynamics (CFD) and Computational Structural Mechanics (CSM) performances of both rotors. The designed rotors satisfy a 20% safety margin to the yielding strength of titanium. A pressure ratio of 3.07 is achieved with an overall efficiency of 72.4%. A comparison between the through-flow model and the CFD-based optimized shape is made, illustrating a very close match in velocity distributions and losses. It shows that the through-flow code is able to identify an optimal configuration for highly-loaded turbomachines and only needs a small refinement in the subsequent CFD-based optimization. The developed methodology allows to produce innovative configurations at a reduced time-to-market cost compared to traditional designs.