A Study on Fluid Excitation Forces Acting on a Rotated Square Tube Bundle of $T∕D=3.1$ in Cross-Flow

The local fluid excitation force acting on a rotated square tube bundle having transverse pitch-to-diameter ratio of $T∕D=3.1$⁠, in a single-phase cross-flow was measured, and the normalized power spectral density (NPSD) and correlation length in the axial direction of a tube were examined. The fluid excitation force acting on the interior tube was from three to ten times larger than that acting on the upstream tube. The fluid force was almost fully developed after the third row. NPSD of the fluid excitation force could be almost plotted on a single universal curve. Regarding the lift direction, there was a peak in NPSD at $fD∕u∼0.3$ caused by vortex shedding. Regarding the drag direction, there could be another peak in NPSD around twice the vortex shedding frequency. In the region of $fD∕u>0.5$⁠, where the effect of the vortex shedding was assumed to be small in the lift direction, the correlation length of the lift direction was $∼1.1D$⁠. NPSD was a little larger than previous results for tube bundles of relatively small pitch to diameter ratios summarized by Axisa, Antunes, and Villard (1990, J. Fluid Struct., 4, pp. 321–341).