8 C. Jin, I. Potts, D. C. Swailes, M. W. Reeks 2.3 Flow configuration of in-line tube-banks The flow configuration is shown in figure 1 and the coordinate system depicted in figure 2. Flow is from left to right and normal to the cylinder axis. The computational domain is of size L$_{x}$ × L$_{y}$ × L$_{z}$ = 28 D × 16 D × 2 D , where D denotes the cylinder diameter. This configuration is based on the second test case considered in Shim[27] which measures surface pressure distributions and fluctuating lift forces and was performed in a suction-type wind tunnel. It consists of four-column in-line tube bundles with transverse pitch-to-diameter ratio ( P$_{T}$/D ) S$_{T}$ of 2.67 and longitudinal pitch-to-diameter ratio ( P$_{L}$/D ) S$_{L}$ of 2.31, respectively. The Reynolds number Re$_{o}$ based on the free stream velocity U$_{o}$ and the cylinder diameter D equals to 9600, and Re$_{g}$ based on the gap streamwise velocity between two cylinders is equal to 15200. The Navier-Stokes solver used in this work uses a cell-centered, collocated grid arrangement finite-volume (FV) discretization method. All spatial terms in the momentum equations are dis- cretized by the bounded central differencing scheme, which not only boasts the advantage of low numerical diffusion of central-differencing scheme but also eliminates unphysical oscillations in the solution fields. The spatial discretization scheme is based on a multi-dimensional, least squares cell-based gradient reconstruction scheme to guarantee a second-order spatial accuracy. In order to prevent unphysical checker-board pressure field, This study employs a procedure similar to that proposed by Rhie and Chow[38]. The Gear’s implicit, three-level second-order accurate scheme is employed for temporal discretization. A generalized fractional-step method is employed for the overall time-advancement. The computational grid is evident in figure 3. The total number of grid elements used for the present simulation is 2730240. the mesh has an embedded region of fine mesh designed for each cylinder in order to enhance the mesh resolution near the cylinder without incurring too large an increase in the total number of mesh elements. 96 grid points hence are allocated along the cylinder surface. The gird spacing on the cylinder in the radial, circumferential, and spanwise direction are Δr/D = 1 . 4 × 10 − $^{2}$, Δθ/D = 3 . 27 × 10 − $^{2}$, Δz/D = 5 . 0 × 10 − $^{2}$, respectively. The first cell adjacent