A Numerical Investigation of Turbulent Flow Over Single and Tandem Square Cylinders

This paper presents the three-dimensional flow investigations over the square cylinders placed in the tandem arrangement. Two different flow configurations were investigated in detail; one comprising of a single square cylinder and the other comprising of three square cylinders placed in a tandem arrangement with the spacing of six times the width (w) of each square cylinder. The Reynolds number based on the width of the square cylinder (w) and free stream velocity (Uo) is 22,000. The problem was solved numerically using an Unsteady Reynolds-Averaged Navier-Stokes (URANS) based model and Large Eddy Simulation (LES) based model. Strouhal Number, lift, and drag coefficients were computed for each configuration. By comparing both the models using contour plots of pressure, velocity and vorticity it is found that the LES model is more accurate to capture the turbulence around single and tandem square cylinders. In the tandem arrangement, complex periodic vortex shedding was observed in the wake of each square cylinder. The production of turbulent kinetic energy was also investigated to understand the roles of stresses during flow over the cylinders. The analysis showed that the production of turbulence by normal stresses is higher than that of shear stresses. Furthermore, it was observed that the flow over the first cylinder arranged in tandem is quite identical to that of the single square cylinder. Moreover, the upstream cylinder experienced a higher lift in comparison to the downstream cylinders.

Fluid dynamics around three cylinders in presence of small control cylinders

A numerical study is performed to analyze the effect of small control cylinders on fluid force reduction and vortex shedding suppression on the flow past three inline square cylinders using the lattice Boltzmann method. The Reynolds number Re = 160 is fixed while the spacing between the cylinders is taken in the range of 1.0D ≤ g* ≤ 5.0D (where D is the size of the main cylinder) and the control cylinder size is varied from 0.1D to 0.5D. To systematically understand the effect of control cylinders on the forces, a detailed analysis of Strouhal number (St), mean drag coefficient (CDmean), and root mean square values of the drag and lift coefficients is presented in this paper. In this study, it is observed that the average mean drag coefficient (CDmeanaverage) and Strouhal number reached either maximum or minimum values at different values of separation ratio (g*) and small control cylinder size (d). It is found that at (g*, d) = (5.0, 0.0) and (1.0, 0.5), the average CDmean attains its maximum (CDmeanaverage = 0.7813) and minimum (CDmean = 0.0988) values. Furthermore, at (g*, d) = (5.0, 0.3) and (2.0, 0.0) the average St attains its maximum (St = 0.1780) and minimum (St = 0.041) values. It is found that the flow regimes completely change in the presence of control cylinders. In particular, at g* = 4.0 there is a critical flow regime when the size of the control cylinder changes from 0.1 to 0.5. The sudden jump in the mean drag coefficient and Strouhal number for the middle cylinder with their maximum and minimum values also confirms the critical flow regime. The effect of control cylinders within tandem square cylinders has not been studied before.