Variational mode decomposition-based characterization of transient aerodynamic forces on a 3:2 rectangular prism in accelerating flow

Accelerating flows represent a critical non-stationary condition that can induce significant transient aerodynamic effects, potentially causing substantial damage to buildings and structures. This study investigates the impact of accelerating flow on a 3:2 rectangular prism, with particular emphasis on the acceleration-induced transient characteristics of the aerodynamic lift forces at a representative wind attack angle. Through validated computational fluid dynamics simulations, aerodynamic forces are systematically examined under various accelerating flow conditions, including variations in initial/final wind speeds and acceleration durations. The variational mode decomposition method is employed to effectively resolve the complex aerodynamic response into three principal components: a time-varying mean component comprising quasi-steady and an acceleration-induced terms; an attenuated fluctuating component directly correlated with flow acceleration; and a stable fluctuating component preserving quasi-steady features. Analysis reveals that transient effects predominantly manifest in the first two components, for which mathematical formulations are derived and distinct time lags in response to flow acceleration are characterized. Moreover, the observed reduction in equivalent Strouhal number indicates that flow acceleration delays vortex shedding. These findings provide fundamental insights into transient aerodynamics behavior under accelerating flow conditions.