Investigation of coherent structures around a surface-mounted tripile cylinder array

The present study examines turbulent flow around a three-dimensional tripile submerged foundation experimentally, using laser Doppler velocimetry, and numerically, using Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) techniques. The study is conducted at a Reynolds number of 104 with a tripile spacing ratio of 3. Flow measurements are compared to assess the predictive capabilities of the selected turbulence models. All RANS models succeeded in predicting primary mean flow phenomena, including flow detachment, vortex recirculation, and downstream reattachment. The LES model performed adequately well both near-wake and far-wake regions. Within the near wake region, the standard k−ϵ model exhibited the largest deviation from experimental data, although it performed appropriately well in the far-wake region. The k−ω shear stress transport model overpredicted the wake recovery. The observed discrepancies are likely due to limitations in modeling flows with large pressure gradients. Also, detailed structural analysis was conducted using the instantaneous flow data obtained from the LES simulations. Key flow features such as the horseshoe vortex, arch vortex, and a dipole structure composed of counter-rotating vortices are identified, exhibiting qualitative agreement with previous high-Reynolds number studies on an isolated cylinder. Instantaneous flow visualization revealed an antler-shaped vortex structure in the downstream wake, which resulted from the interaction of streamwise and spanwise vortices. Time-averaged surface streamlines were used to identify saddle points, attachment nodes, and swirl patterns on the tripiles. Notably, visualization at the free end of the downstream cylinder showed inward-shifted foci and a crescent-shaped recirculation region.