Spatio-temporal behavior of long submerged bluff bodies located near a wall

This study focuses on a comprehensive evaluation of the spatiotemporal dynamics of near-wall submerged bluff bodies, building upon the work of Edegbe et al. [Phys. Fluids 36(11), 115182 (2024)]. Three objects of the same cross-sectional area (W × h, where width, W = 1.4h, height = h) with a constant gap (C) between the body and the bed were investigated. The streamwise length (L) was varied to yield L/h = 1, 2, and 3. The flow characteristics were evaluated under the influence of a boundary layer-like approach flow with δ/h=3.6. The analysis employs instantaneous flow visualization, reverse flow area mapping, two-point spatial correlation, joint probability density functions, and spectral proper orthogonal decomposition (SPOD) to identify dynamic flow features that were not previously reported. The instantaneous flow visualization using Galilean decomposition and spanwise vorticity contour shows the presence of counterclockwise rotating backflow vortices returning to the top surface for the shortest streamwise length (L/h = 1), a characteristic that is absent for L/h = 2 and 3. Interestingly, a noticeable variation is observed in the size of these rotating backflow vortices at different time instances. The reverse flow area analysis further corroborated the intermittent flow reattachment phenomenon observed on the top surface for L/h = 2. Spectral proper orthogonal decomposition (SPOD) analysis revealed that as streamwise length increases, vortical structures become less intense, with L/h = 3 exhibiting the most rapid dissipation of turbulent fluctuations, highlighting the stabilizing influence of the body elongation on wake dynamics.