# Flutter Mechanism of a Thin Plate Considering Attack Angles
###### Abstract  
It is well known that the flutter performance of a section is sensitive to the changing wind angles of attack. Exploring the thin plate's flutter mechanism under different angles of attack is excellent, which helps understand inner flutter characteristics and ensures structural safety. This study investigated flutter derivatives of a thin plate with an aspect ratio of 40 under different wind angles of attack via the forced vibration technique. The otherness of aerodynamic damping and phase lag under different wind angles, which helps in understanding the flutter mechanism, are analyzed using the bimodal-coupled flutter method. It is shown that coupled vertical-torsional flutter dominated the flutter modality under \(0^{\circ}\) and \(3^{\circ}\) wind angles of attack. The critical flutter velocity dramatically decreased with increasing wind angles of attack which is attributed to the increasing negative aerodynamic damping induced by coupled self-excited forces and the decreasing positive aerodynamic damping induced by uncoupled self-excited forces. Moreover, the vertical motion lags behind the torsional motion under the \(7^{\circ}\) angle of attack, which was totally contrary to other angles of attack. Major works in this study reveal the aerodynamic mechanism of the weakened flutter performance of thin plates under large wind angles of attack and provide a reference for the flutter analysis of thin plates. thin plate; flutter mechanism; wind angle of attack; aerodynamic damping; motion state 00000-0000-0000-0000-0000-0000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-00000-000000-00000-00000-00000-000000-00000-000000-000  
and investigated the flutter mechanism of thin plates [10]. Using the Beddoes-Leishman aerodynamic model, [PERSON] investigated the flutter boundary of rotating horizontal wind turbine blades [11]. [PERSON] proposed a bimodal-coupled flutter closed-form solution, offering precise theoretical insight into flutter mechanisms [12; 13; 14]. Based on the existing research, studies on the flutter of plates are primarily limited to cases with a 0\({}^{\circ}\) angle of attack. In contrast, research on non-zero or larger angles of attack remains relatively scarce. However, investigating the flutter characteristics of plates at non-zero angles of attack is equally crucial. For instance, the design of airfoils aims for a high lift-to-drag ratio, and the maximum lift coefficient is typically attained at a moderate angle of attack (e.g., 6\({}^{\circ}\)). Under such conditions, the flutter performance of the airfoil becomes particularly critical. Non-zero angle-of-attack inflows also influence wind and steam turbines' large aspect ratio blades. Furthermore, the prominent angle-of-attack characteristics of mountain winds and typhoons make the wind's attack angle a primary consideration in the wind-resistant design of large-span bridges in mountainous areas [15]. Because of the equivalent aerodynamic section of streamlined box girders, studying the flutter characteristics of plate sections at different angles of attack can offer significant insights into the wind-resistant design of bridges under extensive angle-of-attack conditions. Although some scholars have studied the fluid-structure interaction characteristics, linear and nonlinear aerodynamic characteristics, and flutter derivatives of thin plate sections under different angle-of-attack inflows, research on the flutter mechanisms of thin plates at different angles of attack still needs to be studied [16]. Considering the insufficient research on the flutter characteristics of thin plate sections at different angles of attack, this paper, based on the flutter derivatives of thin plate models at various wind attack angles, employs a dual-mode coupled flutter analysis method to investigate the variations in aerodynamic damping, modal frequency, and coupled motion phase at different angles of attack.