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Experimental investigation of an oscillating hydrofoil propulsion system
Title
Experimental investigation of an oscillating hydrofoil propulsion system.
Creator
Viswanathan, Hariharan., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
An experimental investigation of an oscillating hydrofoil propulsion system working behind a model of a small submersible was conducted. Tests were carried out both for a single foil and for systems of two foils. The tests with two foils considered various possible interactions between the foils. In order to understand the influence of trailing vortices of the foils on efficiency of the propulsion system, the two foils were tested for three different combinations of their relative wing spans....
Show moreAn experimental investigation of an oscillating hydrofoil propulsion system working behind a model of a small submersible was conducted. Tests were carried out both for a single foil and for systems of two foils. The tests with two foils considered various possible interactions between the foils. In order to understand the influence of trailing vortices of the foils on efficiency of the propulsion system, the two foils were tested for three different combinations of their relative wing spans. All of the above tests were carried out for two types of foil motion, one in which the pitch distribution was prescribed and the other in which the pitch depended on the motion characteristics.
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Date Issued
1991
PURL
http://purl.flvc.org/fcla/dt/14695
Subject Headings
Underwater propulsion, Submersibles, Hydrofoil boats
Format
Document (PDF)
Tearing of an aligned vortex by a current difference in two-layer quasi-geostrophic flow
Title
Tearing of an aligned vortex by a current difference in two-layer quasi-geostrophic flow.
Creator
Parthasarathy, Balaji., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A study of two-layer quasi-geostrophic vortex flow is performed to determine the effect of a current difference between the layers on a vortex initially extending through both the layers. In particular, the conditions under which the current difference can 'tear' the vortex are examined. In the first set of flows studied, the current difference is generated by a (stronger) third vortex in the upper layer located at a large distance from the (weaker) vortex under study. A set of flows are also...
Show moreA study of two-layer quasi-geostrophic vortex flow is performed to determine the effect of a current difference between the layers on a vortex initially extending through both the layers. In particular, the conditions under which the current difference can 'tear' the vortex are examined. In the first set of flows studied, the current difference is generated by a (stronger) third vortex in the upper layer located at a large distance from the (weaker) vortex under study. A set of flows are also considered in which an ambient geostrophic current difference is produced by a non-uniform background potential vorticity field. The results of the study will be useful in determining the conditions under which large geophysical vortex structures, such as cyclones and ocean rings, can extend to large depths even though the mean currents in the ambient flow change significantly along the vortex length.
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Date Issued
1993
PURL
http://purl.flvc.org/fcla/dt/14909
Subject Headings
Vortex-motion, Fluid dynamics, Boundary layer control, Flow visualization
Format
Document (PDF)
Vortex street wakes downstream of truncated and full cylinders in a rotating fluid
Title
Vortex street wakes downstream of truncated and full cylinders in a rotating fluid.
Creator
Leader, Bram., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
An experimental study has been conducted to examine the flow field about and the wake behind truncated cylindrical obstacles of varying height, which are towed through a fluid with a free surface in a rotating system. The results show the development of a vortex street-type wake downstream of the obstacle for retrograde (westward) flows, even for very small ratios of obstacle height to water layer depth. For short obstacles, a pronounced backward flowing jet is observed, which impinges on the...
Show moreAn experimental study has been conducted to examine the flow field about and the wake behind truncated cylindrical obstacles of varying height, which are towed through a fluid with a free surface in a rotating system. The results show the development of a vortex street-type wake downstream of the obstacle for retrograde (westward) flows, even for very small ratios of obstacle height to water layer depth. For short obstacles, a pronounced backward flowing jet is observed, which impinges on the Taylor column from downstream. Prograde (eastward) flows are found to have a meandering wake that extends farther than eight obstacle diameters downstream and do not exhibit backjetting or vortex street formation. Upwelling is believed to occur within the side boundary layers of the Taylor column, which could play a significant role in deep water production in the ocean.
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Date Issued
1992
PURL
http://purl.flvc.org/fcla/dt/14827
Subject Headings
Taylor vortices, Fluid dynamics, Vortex-motion
Format
Document (PDF)
experimental study of vortex response during cutting by a blade or cylinder
Title
An experimental study of vortex response during cutting by a blade or cylinder.
Creator
Krishnamoorthy, Srikanth., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
An experimental study of the vortex response to interaction with and cutting by a thin flat plate or circular cylinders of various diameters has been performed. The direction of motion of the flat plate (or circular cylinder) is normal to the vortex axis in the experiments. The vortex is generated by withdraw of fluid at an orifice at the bottom of an "inner cylinder" immersed in a rectangular tank, and the flow field is visualized with both water soluble and immiscible dyes. In the...
Show moreAn experimental study of the vortex response to interaction with and cutting by a thin flat plate or circular cylinders of various diameters has been performed. The direction of motion of the flat plate (or circular cylinder) is normal to the vortex axis in the experiments. The vortex is generated by withdraw of fluid at an orifice at the bottom of an "inner cylinder" immersed in a rectangular tank, and the flow field is visualized with both water soluble and immiscible dyes. In the experiments with circular cylinders, the bending of the vortex is compared to computational predictions from [15], and the mechanism of subsequent breakup of the vortex as it gets closer to the cylinder is studied. The vortex is observed to bend farther without breakup for larger forward speeds of the circular cylinder. Very little bending is observed when the vortex interacts with the flat plate, except for angles of attack exceeding the stall limit Following cutting of the vortex by the flat plate or circular cylinder, a vortex shock is observed to form and propagate up the vortex axis. No vortex shock is observed on the opposite side of the blade. The various forms of these vortex shocks have been photographed, and they appear very similar to travelling vortex breakdowns. The propagation speed of the shocks is compared to an analytical solution for instantaneous vortex cutting by a flat plate of zero thickness.
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Date Issued
1993
PURL
http://purl.flvc.org/fcla/dt/14977
Subject Headings
Vortex-motion, Blades--Noise, Cylinders, Rotors (Helicopters), Helicopters--Noise
Format
Document (PDF)
Computations of normal vortex interaction with blades and circular cylinders
Title
Computations of normal vortex interaction with blades and circular cylinders.
Creator
Yalamanchili, Ramakrishna., Florida Atlantic University, Marshall, Jeffrey S., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
Abstract/Description
A numerical model for the simulation of three-dimensional normal blade-vortex interaction has been developed to study the bending and variation of core radius of the vortex due to the influence of the blade and the subsequent unsteady force on the blade. For thin blades, a procedure to enable instantaneous cutting of the vortex has been employed to study the vortex response to cutting. The vortex is represented by a filament model which includes axial flow within the core and non-uniform core...
Show moreA numerical model for the simulation of three-dimensional normal blade-vortex interaction has been developed to study the bending and variation of core radius of the vortex due to the influence of the blade and the subsequent unsteady force on the blade. For thin blades, a procedure to enable instantaneous cutting of the vortex has been employed to study the vortex response to cutting. The vortex is represented by a filament model which includes axial flow within the core and non-uniform core area. The vortex is convected with self-induced velocities given by the Biot-Savart line integral, and the effect of the cylinder is obtained using a vortex sheet panel method. The governing equations for the vortex axial velocity have a form similar to that of the one-dimensional gas dynamics equations and admit "shock-like" discontinuities. The results indicate that the amount of vortex bending due to interaction with the blade is primarily dependent on the ratio of blade thickness T to ambient vortex core radius sigma o, although for a given amount of bending of the vortex axis, increase in cylinder forward speed results in a decrease in vortex core radius. For blades with T/sigma o < 0(1), very little bending is observed for attack angles under the stall limit. In the case of vortex cutting by a blade, vortex shocks and expansion waves are observed to propagate on the vortex axis away from the blade.
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Date Issued
1993
PURL
http://purl.flvc.org/fcla/dt/14985
Subject Headings
Helicopters, Blades--Noise, Rotors (Helicopters), Vortex-motion
Format
Document (PDF)