An LES study and ... in-line tube-banks 15 of a higher pressure coefficient which results from higher separation velocities in confined flow situations ([42]) as shown in figure 8. In the light of the foregoing discussion it becomes evident that the C$_{D}$ for the downstream cylinders would be much higher than an unconfined circular cylinder as well. Nevertheless, com- pared with the standard value C$_{D}$ = 1 . 185 ([41]), table 2 shows comparable values for C$_{D}$ . Thus, it seems reasonable that the transverse pitch ratio S$_{T}$ = P$_{T}$/D = 2 . 67 does not give rise to the same effect on the drag for the downstream cylinder as for the first column. However, in the present study, the approaching stream for different column cylinders is of different turbulence level which brings about appreciable effects on the vortex shedding and drag force. For example, the free stream for the first column cylinder is assumed uniform. Whilst the downstream cylinders encounter significantly high turbulence level because they lie in the wake. Hence, the blockage ration and the turbulence level of approaching stream, two conflicting factors, result in a drag coefficient C$_{D}$ for the downstream cylinder which is not significant different from an unconfined circular smooth cylinder. This is demonstrated in figure 8 which shows C$_{D}$ for cylinder C2, C3, C4 is significant lower than the value of C1. In selecting extra experimental data, the focus is given to those measured on a single circular smooth cylinder in free stream flow or in confined flows with a comparable blockage ratio to the present configuration. The data for C ′ L from Norberg[40] are determined by the following Table 2: Comparison of results for C$_{D}$ and C ′ L Case C$_{D}$ C ′ L C$_{D}$ C ′ L Based on u$_{g}$ Based on u$_{o}$ Present LES C1 0.767 0.228 1.941 0.579 C2 0.404 0.655 1.022 1.656 C3 0.454 0.650 1.146 1.645 C4 0.464 0.507 1.174 1.284 Experiments Estimated Estimated C1 0.799 0.05-0.08 2.022 0.127-0.202 [27] C2 0.324 0.55-0.65 0.820 1.391-1.645 C3 0.465 0.60-0.70 1.176 1.518-1.771 C4 0.476 0.52-0.60 1.204 1.316-1.518 Emp.correlation Re = 15270 Re = 9600 [40] 0.520 0.520 Experiments Blockage ratio = 1/4 [42] 1.35-1.40 0.80-0.90