Flow-induced vibration characteristics of a square cylinder with normal slit offset at low Reynolds number

Flow-induced vibration (FIV) of bluff bodies is a critical fluid–structure interaction problem, with square cylinders susceptible to large amplitude responses due to their sharp corners. The present study numerically investigates the FIV characteristics of a two-dimensional elastically mounted square cylinder with a normal slit at a low Reynolds number of 170. The study covers a parametric set of calculations including six different slit offset positions (−0.3≤δ/D≤+0.3), measured from the geometric center of the cylinder and the effect of slit width (0≤S/D≤0.4) on vibration and frequency responses, and the associated flow dynamics. Furthermore, a range of reduced velocities (3≤Ur≤30) is considered to characterize the vortex-induced vibration (VIV) and galloping responses. The results show that the normal slit induces periodic suction and blowing, thereby modifying the wake dynamics and FIV response. The results suggest that normal slit can suppress or increase the FIV response depending on the slit offset position. Offsetting the slit toward the front stagnation point (δ/D<0) maintains the enhanced VIV response of the centered slit case (δ/D=0) and suppresses galloping, while offsetting it toward the rear stagnation point (δ/D>0) weakens VIV and enhances galloping. In the VIV regime, δ/D<0 sustains strong near-wake vortex formation through enhanced slit-wake interaction, whereas δ/D>0 shifts the vortex formation downstream and reduces the fluctuating lift. For δ/D<0, the response transitions from galloping to the secondary VIV regime. Wavelet analysis further shows that δ/D<0 strengthens wake mode (WM) dominance, whereas δ/D>0 weakens WM dominance and enhances structural mode control, promoting large amplitude galloping.