Numerical Analysis of Two Square Cylinders of Different Sizes With and Without Corner Modification
Authors: Gowda Y. T. Krishne , Ravindra Holalu Venkatdas , Chowdeswarally Krishnappa Vikram 
Published: February 2017

Flow past square cylinders has attracted a great deal of attention because of its practical significance in engineering e.g., High rise buildings, monuments and towers. Similarly, bridge pillars, and legs of offshore platforms are continuously subjected to the load produced by maritime or fluvial streams. The presence of separated flows, reattachment, formation the vortices, un steadiness of flow, mass and momentum transfer across shear layer makes the flow field quite complex. Many research work was carried out for a single square cylinder and flow past two square cylinders, but with corner medications in square cylinder of different size arranged in tandem was not taken up. This has motivated to take up the flow past two different sized square cylinders i.e., smaller in upstream and larger in downstream which is numerically simulated by using Fluent software. Reynolds number of 100 and 200 is considered for the investigation. The flow is assumed to be two dimensional, unsteady and incompressible. The computational methodology is carried out once the problem is defined, the first step in solving the problem is to construct a geometry then proper assignment of boundaries are set. After setting the boundary types, the geometry is discretized into small control volumes. Once the surface mesh is completed by using Gambit software, the mesh along with boundary conditions are exported to fluent, which is CFD solver usually run in background mode. The run would continue until the required convergence criterion is reached or till the maximum number of iterations is completed. Results indicate, in case of chamfered and rounded corners in square cylinders of different size, there is decrease in the wake width and thereby the lift and drag coefficient values. The lift coefficients in Square cylinders of different size with corner modifications decreases but Strouhal number increases when compared with a single square cylinder without corner modifications. Frequency of vortex shedding decreases with the introduction of second cylinder either in the upstream or downstream of the first cylinder. As the centre distance between two square cylinders i.e., PPR (pitch to perimeter ratio) with and without corner modifications is increased to 6, the flow velocity almost approaches to flow past a single square cylinder with and without modifications for same condition. When the size of the upstream square cylinder with and without modifications is smaller than that of the downstream square cylinder, the size of the eddies is always smaller in between the cylinders compared to the downstream of the second cylinder. The flow velocity in between the cylinders with and without corner modifications are less compared to the downstream of the second cylinder. Pressure on the downstream side of the cylinder is smaller than that on the upstream side of the cylinder for with and without corner modifications. Also, the front portion of the cylinder is experiencing highest pressure compared to the second cylinder for all the three cases i.e., PPR = 2, 4 and 6. Pressure at the upper side, bottom side and back side of square cylinder with and without corner modifications is of negative pressure, it is because of vortices generated at that surfaces. The downstream cylinder is found to experience higher lift compared to the upstream cylinder. The results are presented in the form of while the downstream cylinder is found to experience higher drag compared to the streamlines, flow velocity, pressure distribution, drag coefficient, lift coefficient and strouhal number.