Date of Award

10-11-2024

Publication Type

Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Gap flow;Particle Image Velocimetery;Reynolds number

Supervisor

Ghassan Nasif

Supervisor

Ram Balachandar

Abstract

This study investigates the impact of gap ratio and Reynolds number on the wake dynamics of flow past a horizontal cylinder using Particle Image Velocimetry. The gap ratios (ratio of gap size, �� to cylinder diameter, �� ) examined were 0.50,1.0, and 1.5 at Reynolds number of 3960 and 0.25, 0.50, and 1.0, at Reynolds number of 7930. The findings reveal that a decreasing gap ratio results in an asymmetrical wake due to the stretching of the bottom cylinder shear layer and an increase in recirculation length behind the cylinder due to reduced entrainment. Additionally, the recirculation region length decreases with increasing Reynolds number due to enhanced mixing and momentum transfer. No recirculation zone near the bed was observed for the Reynolds numbers considered. Proper Orthogonal Decomposition (POD) analysis showed reduced energy contribution of the first two modes with decreasing gap ratio, reflecting the breakdown of large coherent structures due to the bed interaction. The reconstructed flow field indicated suppression of vortex shedding from the bottom cylinder shear layer for gap ratios less than 0.50. These results suggest that gap ratio is a more critical parameter than absolute gap size in determining flow structures, with minimal effect from Reynolds number.

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