Session: 10.4.1 - Vortex Dynamics I

Paper Number: 151952

151952 - Experimental Investigation of Flow Dynamics of Chamfer on a Wall Mounted Square Cylinder 

Abstract: 

The flow behaviour around the bluff bodies has special interests of researchers. As the technology is getting advanced more accurate techniques are being used to study the flow dynamics around and in the wake of bluff bodies placed in uniform flow. Numerous studies have been performed on flows around a square cylinder by doing corner modifications as we can see a lot of practical applications and scenarios like that. The flow pattern is observed when a cylinder of a set height is placed in a flow that resembles many real-world practical applications like a wind flowing past a building, supports of bridges in rivers, cooling of electrical components in a heat sink, and cooling towers among the few. When fluid and a bluff body like a square cylinder interact, they produce complex flow structures in the wake downstream of flow. The height-to-boundary layer ratio, aspect ratio, and flow variable greatly affect the flow structures and it is therefore necessary to understand the relation between the above-mentioned parameters and the interaction between the cylinder and fluid. Various forces are introduced during the bluff body and fluid interactions such as lift and drag which can induce vibrations and dynamic loading which can be harmful to the structure. These types of vibrations must be reduced for the safety and longevity of the structure. So, we can see that the flow around a square cylinder especially with corner modifications is very significant and therefore is studied by many researchers.

Wake characteristics of a wall-mounted finite height square cylinder were studied having different chamfer dimensions. This study was performed using a non-intrusive technique called Particle Image Velocimetry (PIV) in a closed-loop water tunnel with a turbulent intensity of less than 1%. The study focused on the flow behavior with changes in chamfer dimensions both upstream and downstream of the cylinder, horseshoe vortex and Von-Karman vortices, etc. Different cylinders were used having variable chamfer dimensions while fixing the diameter, aspect ratio (AR) for all cylinders, and Reynold’s number (Re). With the introduction of chamfer, it was found that the chamfer dimension significantly influences the characteristics of flow around the wall-mounted cylinder, and upwash flow increased significantly thus affecting the vortex structures in the wake of the cylinder.

A wall-mounted three-dimensional cylinder was placed in a boundary layer having an aspect ratio of 3 with different chamfer dimensions i.e. 0d, 0.1d, 0.2d, 0.3d. Corner modification showed a decrease in wake region when compared to square cylinder thus improving flow. The backplane showed that by increasing the chamfer dimension the upwash flow increased significantly. From the time-averaged streamlines, it can be inferred that the upwash flow interacts with the symmetric Von-Karman vortices at low height i.e.0.25h reducing their size and strength. The core of the upwash vortex didn’t move downstream but moved away from the bed. Also, the downwash increased pushing the saddle point a bit further downstream. While the vortices at 0.5h weren’t affected by the upwash or downwash. Introducing the chamfer also narrowed the wake. This was also confirmed by the point of maximum velocity as it moved downstream and closer to the central axis of the cylinder.

Moreover, the horseshoe vortex at upstream of the cylinder was also reduced in size and strength by the introduction of the chamfer dimension respectively. This study reveals that wake dynamics is important for bluff body dynamics and in-depth analysis is very important for understanding the underlying physical phenomenon.

Presenting Author: Usman Latif NUST

Presenting Author Biography: Usman Latif received his PhD degree in Mechanical Engineering/Fluid Dynamics (Fluid Structure Interaction) in 2021 from NUST Islamabad, Pakistan. He conducted his research in a joint program at Duke University, USA. Now, he is doing research with Dr. Earl H. Dowell (Duke University). His research interests are related to the design, evaluation, and experimental investigation of piezoelectric nano-generators based energy harvesting for low energy consuming devices like unmanned vehicles, monitoring, data logging sensors, and MEMS.