Numerical investigation of different aspect ratios for flow past three inline rectangular cylinders

Abstract

In this paper, numerical investigations are carried out to study the effect of aspect ratios (AR = length/height) for flow past three rectangular cylinders aligned inline at different gap spacings (g) using lattice Boltzmann method. The aspect ratio is varied between 0.25 and 3, gap spacing is taken in the range from 0.5 to 7 and the Reynolds number is fixed at 150. With the help of present numerical investigation, it is found that the variation of forces with different AR and g is governed by six distinct flow patterns: (1) shear layer reattachment flow; (2) steady flow; (3) quasi-steady flow; (4) strongly interactive vortex shedding flow; (5) two-row vortex street flow; and (6) critical flow pattern. It is observed that the development of vortices, interferences of the free shear layers and the wake vortices distribution of three cylinders play a vital role in the variation of shedding frequencies and fluid forces. Consequently, the cylinders placed at downstream usually experience serious fluctuating forces due to unsteady wakes generated by the upstream cylinders. Also, the upstream cylinder normally experiences larger mean drag force as compared to the downstream ones. The sudden jumps in mean drag coefficients and Strouhal numbers with their maximum and minimum values are identified, respectively. The upstream and middle cylinders force coefficients strongly affected due to critical aspect ratios at different fixed gap spacings. It is observed that the wake transition at early stages significantly changes by changing the aspect ratios for fixed gap spacings. The results also show that the middle and downstream cylinders experience negative drag force for some aspect ratios and gap spacings. Furthermore, the dependence of the critical gap spacing on the aspect ratios is also discussed.

Analysis of the wake mechanism in external flow around tandem bluff bodies with different aspect ratios

“…The flow around two tandem rectangular cylinders with distinct aspect ratios was simulated at Re = 100 by considering different values of G progressively varying from 0.25 to 20. From previous studies, we can conclude that the flow structure mechanism around multiple rectangular cylinders appears to be a complicated phenomenon that depends on several parameters, including Re, G, and AR (Islam et al, 2018;Rahman et al, 2021). In the current study, the resulting flow regimes are specified into different patterns in terms of the creation of different shape vortices, wake structure mechanism, and the behavior of shear layers detaching from cylinder corners and interacting with each other.…”

“…Therefore, we considered the 20-point grid for analysis for this study. This grid size follows recommendations based on lattice Boltzmann simulations for both single and multiple objects (Islam et al, 2018;Rahman et al, 2021). Note that the uniform meshing (Δx Δt 1) is selected in the whole computational domain because the standard LBM considers such meshing for simulations without any need to use external mesh generators (Perumal et al, 2012).…”

“…They concluded that wake transitions of multiple cylinders depend not only on Re but also on G. Song et al (2017) observed the flow patterns and force variations over four inline square cylinders by considering Re = 300 and G = 1.5 to 8. They reported that, when G < 3.5, CD mean values for the downstream cylinders increased sharply with increasing G. For G > 3.5, the CD mean values of the downstream cylinders decreased gradually with increasing G. Islam et al (2018) investigated different aspect ratio effects on the flow around three inline cylinders at Re = 150, AR = 0.25 to 3, and G = 0.5 to 7. They observed that, at all G, the CL rms of all cylinders decreased with increasing AR.…”

Extensive study of flow characters for two vertical rectangular polygons in a two-dimensional cross flow

“…The authors presented detailed wake patterns and force coefficient results for different geometrical configurations and Reynolds numbers. Islam, S. U., et al (Islam et al, 2018) presented a comprehensive numerical investigation into the aerodynamic behavior of three inline rectangular cylinders with varying AR = 0.25 to 3 and X G = 0.5 to 7 with Re = 150. They indicated that the AR significantly influences the flow behavior around the rectangular cylinders.…”

Rectangular Cylinder Orientation and Aspect Ratio Impact on the Onset of Vortex Shedding

“…They found that a smaller AR results in higher f D and lower vortex shedding frequencies, while a larger AR leads to the opposite trends. Islam et al [20] discussed the effect of AR ranging from 0.25 to 3 and G ranging from 0.5 to 7 on the flow characteristics of three inline rectangular cylinders with fixed Re = 150. The results showed that the AR strongly affected the force coefficients ( C f ) of the cylinders.…”