Hydrodynamics of flat plates in cross-flow near the free surface

Identifier:  TDX:2933

Handle: https://hdl.handle.net/20.500.11797/TDX2933

Authors:  Satheesh, Sukruth

Abstract:
This thesis presents the results of a study conducted to understand the effect of free surface on forces generated by a flat plate being towed in a quiescent fluid, with the plate surface being normal to the towing direction. The work is based on a parametric study involving aspect ratio, Reynolds number and submergence depth, with the depth always being measured as the distance between free surface and the upper edge of the plate. Force and quantitative flow visualization techniques have been employed to understand the flow physics. It was found that the drag increases abruptly prior subsiding with increasing submergence depth, with this jump in drag being more prominent in low aspect ratio plates. The abrupt rise in the drag is due to the existence of a gap-flow at the free surface resulting in the formation of a recirculating flow in close proximity to the base region of plate. Overall, the trends are Reynolds number independent, except when the aspect ratios are in the range from 0.75 to 1.33, and the plate was near the free surface. Furthermore, two different plate configurations have been investigated. First, rigid plates with porosity at distinct locations and secondly structural flexibility. Both concepts have resulted in significant drag reduction, especially near the free surface. The mechanism of drag reduction for porous models has been shown to be due to the interaction between the jets formed at the holes, the shear layers and the gap-flow. With structural flexibility, reconfiguration leads to drag reduction.