Numerical Simulation of Flow Characteristics Over Two Square Cylinders at Different Diameters with Various Gap Spacing
Waqas Sarwar Abbasi
Raheela Manzoor
Farida Aslam
Noreen Azhar
Abstract
Numerical simulations were conducted to investigate the effect of the upstream cylinder's size on flow characteristics and fluid force reduction. The study involved analyzing the flow around two consecutive, unequal-sized square cylinders arranged in tandem. The simulations utilized the Lattice Boltzmann method and covered various gap spacing’s (g = s/d) ranging from 0.5 to 6. The Reynolds number was kept constant at Re = 150, while the diameter of the upstream cylinder varied among 20, 25, 30, 35, and 40. Prior to examining the effect of the cylinder diameter on flow at different spacing ratios, we assessed the computational domain and grid independence to determine the most accurate computational domain size and adequate grid points. Following this, we performed numerical simulations for different gap spacing’s and cylinder diameters, and obtained results including vorticity and pressure contours, drag and lift coefficients, Strouhal numbers, and other physical parameters. The vorticity contour visualizations revealed distinct flow regimes based on their flow features, which were categorized as follows: i) Single Bluff Body Flow Regime (SBB), ii) Shear Layer Reattachment Flow Regime (SLR), iii) Steady Flow Regime (SF) and iv) Fully Developed Vortex Shedding Flow Regime (FDVS). In terms of physical parameters, we calculated the mean drag coefficient (Cdmean), root mean square of drag (Cdrms), lift coefficients (Clrms), and Strouhal numbers (St) for both cylinders (C1 and C2). The highest mean drag coefficient was observed for the downstream cylinder (C2) at (D, g) = (25, 6), with a value of 1.6531. Similarly, the maximum numerical value of Cdrms was recorded for C2 at (D, g) = (30, 6). Additionally, in some cases, the mean drag coefficient for the downstream cylinder showed negative values due to the thrust effect. Furthermore, due to the varying size of the upstream cylinder (C1) compared to the downstream cylinder (C2), St1 was greater than St2, with this trend observed at (D, g) = (40, 6).