  Citation: Hoyos, J.D.; Jiménez, J.H.; Echavarría, C.; Alvarado, J.P.; Urrea, G. Aircraft Propeller Design through Constrained Aero-Structural Particle Swarm Optimization. Aerospace 2022, 9, 153. https://doi.org/10.3390/ aerospace9030153 Received: 15 January 2022 Accepted: 22 February 2022 Published: 9 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). aerospace Article Aircraft Propeller Design through Constrained Aero-Structural Particle Swarm Optimization José D. Hoyos 1,2, * ,† , Jesús H. Jiménez 3, * , Camilo Echavarría 2 , Juan P. Alvarado 2,4 and Germán Urrea 2 1 School of Aeronautics and Astronautics, University of Purdue, West Lafayette, IN 47906, USA 2 Faculty of Aeronautical Engineering, Universidad Pontificia Bolivariana, Medellín 050031, Colombia; upb.camilo@gmail.com (C.E.); juan.alvarado@upb.edu.co or s3441603@student.rmit.edu.au (J.P.A.); german.urrea@upb.edu.co (G.U.) 3 Department of Aeronautics, Imperial College London, London SW7 2BX, UK 4 Royal Melbourne Institute of Technology, Melbourne 3000, Australia * Correspondence: jhoyos@purdue.edu or jose.hoyos@upb.edu.co (J.D.H.); jesus.jimenez21@imperial.ac.uk (J.H.J.) † Grupo de Investigacion sobre Nuevos Materiales, Universidad Pontificia Bolivariana, Medellín 050031, Colombia. Abstract: An aero-structural algorithm to reduce the energy consumption of a propeller-driven aircraft is developed through a propeller design method coupled with a Particle Swarm Optimiza- tion (PSO). A wide range of propeller parameters is considered in the optimization, including the geometry of the airfoil at each propeller section. The propeller performance prediction tool employs a convergence improved Blade Element Momentum Theory fed by airfoil aerodynamic characteristics obtained from XFOIL and a validated OpenFOAM. A stall angle correction is estimated from exper- imental NACA 4-digits data and employed where convergence issues emerge. The aerodynamic data are corrected to account for compressibility, three-dimensional, viscous, and Reynolds number effects. The coefficients for the rotational corrections are proposed from experimental data fitting. A structural model based on Euler-Bernoulli beam theory is employed and validated against Finite Element Analysis, while the impact of centrifugal forces is discussed. A case of study is carried out where the chord and pitch distributions are compared to minimal losses distribution from vortex theory. Wind tunnel tests were performed with printed propellers to conclude the feasibility of the entire routine and the differences between XFOIL and CFD optimal propellers. Finally, the optimal CFD propeller is compared against a commercial propeller with the same diameter, pitch, and operational conditions, showing higher thrust and efficiency. Keywords: propeller; multidisciplinary optimization; particle swarm optimization; aero-structural optimization; Computational Fluids Dynamics; XFOIL; Blade Element Theory; OpenFOAM 1. Introduction Electric propulsion is leading to a new focus in aircraft design due to the impact of green technologies on climate change. Moreover, drone flights through thinner atmospheres than earth’s one are raising new challenges on what propeller propulsion can achieve [1]. These trends require the development of multi-disciplinary optimal propeller design. The main purpose of this work is to present and test a methodology to design an aero-structural optimal propeller to reduce the energy consumption given a target thrust, airspeed, and environmental conditions. Although the article employs the electric motor equations, a combustion propulsion model can be easily implemented instead [2]. Intending to optimize the electric aircraft performance, high-reliability models for propulsive systems are required. In the present work, a Blade Element-Momentum Theory (BEMT) algorithm with improved convergence and recursive routines is employed for the propeller performance estimation. Additionally, some corrections to the basic model Aerospace 2022, 9, 153. https://doi.org/10.3390/aerospace9030153 https://www.mdpi.com/journal/aerospace