Flow interference between two tripped cylinders

Flow interference is investigated between two tripped cylinders of identical diameter D at stagger angle alpha = 0 degrees similar to 180 degrees and gap spacing ratio P-* (= P/D) = 0.1 similar to 5, where alpha is the angle between the freestream velocity and the line connecting the cylinder centers, and P is the gap width between the cylinders. Two tripwires, each of diameter 0.1D, were attached on each cylinder at azimuthal angle beta= +/- 30 degrees, respectively. Time-mean drag coefficient (C-D) and fluctuating drag (C-Df) and lift (C-Lf) coefficients on the two tripped cylinders were measured and compared with those on plain cylinders. We also conducted surface pressure measurements to assimilate the fluid dynamics around the cylinders. C-D, C-Df and C-Lf all for the plain cylinders are strong function of alpha and P-* due to strong mutual interference between the cylinders, connected to six interactions (Alam and Meyer 2011), namely boundary layer and cylinder, shear-layer/wake and cylinder, shear layer and shear layer, vortex and cylinder, vortex and shear layer, and vortex and vortex interactions. C-D, C-Df and C-Lf are very large for vortex and cylinder, vortex and shear layer, and vortex and vortex interactions, i.e., the interactions where vortex is involved. On the other hand, the interference as well as the strong interactions involving vortices is suppressed for the tripped cylinders, resulting in insignificant variations in C-D, C-Df and C-Lf with alpha and P-*. In most of the (alpha, P-*) region, the suppressions in C-D, C-Df and C-Lf are about 58%, 65% and 85%, respectively, with maximum suppressions 60%, 80% and 90%.