Abstract
A numerical investigation on the effects of separation ratios and Reynolds numbers on the flow around four square cylinders in diamond arrangement has been carried out using the lattice Boltzmann method. The separation ratios between the cylinders vary from g ∗ = 1 to 15. The Reynolds numbers based on the diameter of the square cylinder and the inlet uniform inflow velocity are selected from Re = 80 to 160. The computations show that a total of five different flow regimes are observed over the selected ranges: single bluff-body, quasi-unsteady, chaotic flow, in-phase synchronized vortex shedding, and antiphase synchronized vortex shedding flow regimes. It is found that the flow features significantly depend on both the separation ratio and Reynolds number, with the former’s influence being more than the latter’s. We found that the critical spacing for four square cylinders in diamond arrangement for selected Reynolds numbers (80 ≤ Re ≤ 160) is in the range of 2 ≤ g ∗ ≤ 5. The results reveal that the presence of secondary cylinder interaction frequencies indicates that, for chaotic flow regime, the wake pattern is not stable and there is a strong interaction of gap flows and continuous change in the direction of shed vortices behind the cylinders. The effects of the g ∗ and Re on fluid forces, vortex shedding frequency, and flow separation have been examined in detail.
Highlights
IntroductionStudy on wake structure and fluid forces on multiple bluff bodies is of practical importance in a number of engineering applications, such as chimneys, offshore structures, towers, bridges, marine risers, and ocean platforms
Fluid-structure interactions occur in a number of engineering fields
Similar to that of a flow around an isolated cylinder, a single vortex street is observed behind the cylinders. is flow behavior is named as single bluff-body flow regime (SBBFR). e corresponding time variations of CD and CL for SBBFR are presented in Figures 11(a) and 11(b). is graph clearly indicates that there is no modulation in the signals. e drag coefficient for the C1 is relatively smaller than those for the other three cylinders
Summary
Study on wake structure and fluid forces on multiple bluff bodies is of practical importance in a number of engineering applications, such as chimneys, offshore structures, towers, bridges, marine risers, and ocean platforms. It is of importance in the analysis of fluid/ structure interactions since the mechanism associated with the complex physical phenomena such as vortex shedding, flow separation, merging of vortices, and interaction of gap flows with the shed vortices is still not fully understood. Investigations into the effects of the g∗ and Reynolds number (Re) on multiple bluff bodies have been carried out. Agrawal et al [5] conducted numerical investigation into the effects of g∗ on the flow past two side-by-side square
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