Wake dynamics and control of a square cylinder using finite-span dual rigid splitter plates

This study experimentally investigates the wake dynamics of a two-dimensional square cylinder with dual rigid splitter plates (DRSP) of varying spanwise widths (W/D = 2–∞) at Re = 1.2 × 105. Splitter plates are used for wake stabilization but most studies vary the length and consider the spanwise extent to be infinite, so the three-dimensional effects of a finite-width DRSP—and the resulting edge-induced flow structures are not well understood. This study uses time-resolved particle image velocimetry (TR-PIV) to measure the instantaneous velocity field in the near-wake region and proper orthogonal decomposition (POD), spectral analysis, and vorticity-based flow visualization. The mean streamwise velocity fields feature a deepening of the wake velocity deficit as W/D increases, and there is an increase in the lateral extent. Narrower plates promote a more rapid wake recovery, but wider configurations (W/D ≥ 8) create a deeper and more persistent velocity deficit. The distributions of streamwise and spanwise velocity fluctuations are progressively reduced as W/D increases to a limit if W/D = ∞, at which point, large-scale wake motions are most effectively damped. Turbulent kinetic energy features a similar monotonic attenuation, which shows that there is progressive inhibition of shear–layer interactions as lateral confinement increases. POD analysis shows that there is a consistent modal structure for all cases: Modes 1 and 2 form a classical antisymmetric vortex-shedding pair, and higher-order modes feature lower-energy, less coherent flow structures in the wake. The shape of the mode remains qualitatively similar, but the associated modal energies decrease as W/D increases, which shows that global instability decreases. Spectral analysis of the POD temporal coefficients shows that distinct second and third harmonics (2f1 and 3f1) are present for the W/D = 2 configuration. For intermediate DRSP widths (W/D = 4–8), these harmonic components do not occur, but there is an additional dominant frequency (f2). As the DRSP width increases (W/D = 10 and ∞), the spectra exhibit broadened frequency peaks, which show that there is a loss of discrete harmonic content in the wake dynamics. Instantaneous vorticity fields show that the wake structure evolves continuously and there is no abrupt transition: narrow DRSP widths permit sustained shear–layer communication, but increasing DRSP width progressively leads the wake toward the limiting behavior of an idealized infinite DRSP configuration (W/D = ∞). This is characterized by increased symmetry and the formation of larger, more coherent vortex structures associated with elongated shear–layer development. Increasing W/D progressively weakens the temporal organization of vortex shedding and delays the development of strong shear–layer interactions. As a result, wake unsteadiness is redistributed rather than uniformly suppressed, leading to a continuous and quantifiable transition from strongly interacting near wakes toward a state characterized by weakened shear–layer interaction and an asymptotic wake response at sufficiently large W/D.