J. Fluid Mech. (2023), vol. 967, A18, doi:10.1017/jfm.2023.477 Critical effect of fore-aft tapering on galloping triggering for a trapezoidal body Zhi Cheng 1, 2 , †, Fue-Sang Lien 2 , Earl H. Dowell 1 , Eugene Yee 2 , Ryne Wang 1 and Ji Hao Zhang 2 1 AeroElasticity Group, Pratt School of Engineering, Duke University, 2080 Duke University Road, Durham, NC 27708, USA 2 Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada (Received 18 December 2022; revised 2 May 2023; accepted 7 June 2023) The critical effect of the windward interior angles of elas ti cally mounted trapezoidal bodies on a galloping instability is numerically investigated in this paper using two methodologies of high-fidelity computational fluid dynamics simulations and data-driven stability analysis using the eigensystem realization algorithm. A micro exploration of the dynamical response is processed to understand the mechanism underpinning the structural amplification at the initial stage of the galloping instability and the competition between wake and structural modes. It is observed that very small changes in the windward interior angle of an isosceles-trapezoidal body can provoke or suppress galloping – indeed, a small decrease or increase (low to 1 ◦ ) of the windward interior angle from a right angle (90 ◦ ) can result in a significant enhancement and complete suppression, respectively, of the galloping oscillations. This supports our hypothesis that the contraction and/or expansion (viz., fore-aft tapering and/or widening) of the cross-section in the streamline direction has potential influences on galloping triggering from the geometrical perspective. The data-driven stability analysis is also applied to verify and anal yse this phenomenon from the perspective of modal analysis. The experimental measurements are also conducted in the wind tunnel to support this hypothesis. Key words: flow-structure interactions, instability control 1. Introduction Flow-induced vibration (FIV), a common phenomenon of fluid–structure interaction (FSI), is found everywhere and at all scales in the applications of marine, civil, aero nau ti cal and power engineering (Service 1942; Walker & Sibly 1977; Païdoussis, Price & † Email address for correspondence: vamoschengzhi@gmail.com © The Author(s), 2023. Published by Cambridge University Press 967 A18-1 https://doi.org/10.1017/jfm.2023.477 Published online by Cambridge University Press