Numerical investigation of wake dynamics and flow interference effects on fluid-structure interaction of dual side-by-side rectangular cylinders: A lattice Boltzmann study

• Wake dynamics of dual rectangular cylinders are explored via Lattice Boltzmann Method. • Four distinct flow regimes are identified based on varying gap ratio (0 ≤ g ≤ 8). • Maximum unsteady forces and vortex shedding occur at gap ratio g = 1. • Stable, decoupled flow appears at g ≥ 3 with lowest drag and lift fluctuations. • Results aid aerodynamic design of heat exchangers and bluff body clusters. The aerodynamic interactions between bluff bodies significantly influence fluid-induced forces and vortex shedding, which are critical in various engineering applications such as heat exchangers, offshore structures, and clustered aerodynamic designs. However, the wake dynamics of side-by-side rectangular cylinders (RCs), particularly with varying transverse gap ratios, remain insufficiently understood. This study aims to investigate the effect of gap spacing on wake transitions, hydrodynamic forces, and vortex synchronization phenomena around dual RCs with an aspect ratio of 2:3 at a fixed Reynolds number of 200. A series of two-dimensional incompressible flow simulations was conducted using the Lattice Boltzmann method (LBM) for g ranging from 0 to 8. The analysis incorporated vorticity contours, streamline visualizations, time-domain force coefficient histories, Fast Fourier Transform (FFT) of lift fluctuations, and statistical evaluations of mean and root mean square of drag, and lift, and Strouhal numbers. Grid independence testing and code validation against benchmark cases ensured the reliability of the numerical approach. Four distinct wake regimes were identified as the gap increased: solitary bluff-body, flip-flopping, modulation-synchronized, and in-phase synchronized flows. The highest mean drag (≈1.72) occurred at zero spacing due to maximum flow blockage, whereas the lowest (≈1.12) appeared at g = 3 with reduced interference. Maximum unsteady force fluctuations root mean square value of drag coefficient (Cdrms) ≈ 0.36, root mean square value of drag coefficient (Clrms) ≈ 0.82 and peak vortex shedding frequency (St ≈ 0.217) were observed at g = 1, while the most stable, decoupled flow patterns with minimum fluctuations emerged at larger gaps (g ≥ 3). These results highlight a strong sensitivity of aerodynamic forces and vortex behavior to the transverse gap between rectangular cylinders. The findings provide essential insights for optimizing the design of multi-body systems where flow interference and unsteady forces play a crucial role, such as in thermal energy storage units, compact heat exchanger arrays, and other bluff-body assemblies. Proper tuning of gap spacing can mitigate flow-induced vibrations, reduce drag, and enhance thermal-fluid performance in engineering applications.