Amirkabir University of Technology AUT Journal of Mechanical Engineering 2588-2937 9 2 2025 04 01 Flutter speed prediction of double-sweep folding wing in subsonic airflow 143 166 5665 10.22060/ajme.2025.23196.6113 EN Shahrokh Shams School of Aerospace Engineering, College of Interdisciplinary Science and Technology, University of Tehran, Tehran, Iran. 0000-0002-1259-821X Peyman Falahati School of Aerospace Engineering, College of Interdisciplinary Science and Technology, University of Tehran, Tehran, Iran. Mortaza Salehian Department of Aerospace Engineering and Centre of Excellence in Computational Aerospace Engineering, Amirkabir University of Technology, Tehran, Iran 0009-0004-1439-3260 Journal Article 2024 05 18 This study addresses the prediction of the flutter speed for a double-sweep folding wing in subsonic airflow, an area less explored in past research. Two types of modeling are employed: structural and aerodynamic. The structural model treats the wing as an Euler-Bernoulli beam. For the aerodynamic model, Theodorsen's unsteady aerodynamic theory is used. This theory is initially in the frequency domain but is converted to the time domain using the Kussner function and a new formulation method. Kinetic energy, strain energy, and the work of aerodynamic forces are then calculated. The differential equations governing the wing structure are derived using Hamilton's principle. The wing's motion equation is obtained using assumed modes and the Galerkin method. The instability flutter speed is determined through the p-method, and graphs of frequency versus airflow velocity are plotted. The results indicate that using the Kussner function for variable airflow improves the accuracy of flutter speed prediction. The analysis of sweep angle changes on flutter speed and frequency revealed that sweep angle one has the least positive effect, while sweep angle two has the most positive effect on flutter speed and frequency, respectively. https://ajme.aut.ac.ir/article_5665_f900afc719d7d86bd7d17b9d3be0aafe.pdf