9 An LES study and ... in-line tube-banks to the cylinder is within the range Δy + < 11 . 8 in wall units 1 that satisfies the requirements of the Wener-Wengle wall-layer model for LES. Prior to the present simulation, with the standard Smagorinsky subgrid scale model, a coarser grid simulation were carried out to determine the resolution. With fully developed turbulent flow, periodic boundary conditions are justified to use along the normal ( y ) and spanwise ( z ) direction. For the inlet boundary condition, a simple uniform velocity profile is assumed and the turbulent intensity set to zero. Hence, the turbulence fluctuations at the inlet was not accounted for temporally and spatially. Nevertheless, a length 5 D before the first column bank is used to allow the development of turbulence. At the exit boundary, the solution variables from the adjacent interior cells are extrapolated to satisfy the mass conservation. The simulation is advanced with a non-dimensional time step ΔtU$_{o}$/D ≈ 2 × 10 − 3 that yields maximum Courant-Friedrichs-Lewy (CFL) number of 0.5. For results presented here, the first- order statistics are collected by integrating the governing equations over an interval of 30 D/U$_{o}$ , and all the statistics are averaged over the 40 sampling points along the spanwise direction. To provide an overview of the development of turbulent flow across the four-column in-line tube- banks, wake vortices visualized using the Q criterion (see [39]) are presented first. Then, time- resolved pressure distributions provide quantitative information on surface pressure fluctuations, which are compared with experimental measurements ([27]). Following this, the time histories of coefficient of drag C$_{D}$ and lift are given. The development of vortex shedding behind the cylinder in the middle column are investigated via examining the corresponding energy spectrum in the wake. The coherence of vortex shedding along the length of the middle cylinder is studied through computing the auto-correlation function of each velocity fluctuation component. In the present work, the turbulent flow across tube-banks has been considered to have reached the statistically stationary state after a simulation time of T = 200 D/U$_{o}$ . All the statistics presented here are 1 The superscript + denotes a non-dimensional quantity scaled using the wall variables, e.g. y + = yu$_{τ}$ /ν , where ν is the kinematic viscosity and u$_{τ}$ = $^{√}$τ$_{w}$ /ρ is the wall friction velocity based on the wall shear stress τ$_{w}$ , and which is a velocity scale representative of velocities close to a solid boundary. 3 Results and discussions