Vorticity transfer through rapid area change

Extensive studies have been conducted on the use of biomimetic foils for propulsion and maneuvering of vehicles. These studies, however, mostly focuses on the use of sinusoidal motion similar to bird flapping or fish swimming to generate the necessary forces. Few studies have been conducted to investigate the generation of maneuvering forces by using rapid vorticity transfer into the fluid through a rapid motion as observed in some animals. In this study a NACA 0012 foil was towed steadily at Reynolds number of 14000, then the foil is rapidly accelerated in the transverse direction. Two different cases were tested: One where the area decreases and one where it increases, referred to as vanishing foil and emerging foil, respectively. Various angle of attacks were tested, and in all the cases the circulation is conserved. The method of Particle Image Velocimetry and flow visualization were used to map out the three-dimensional vortical structure after the rapid motion. In the emerging foil experiment the flow structure is similar to the case of accelerating wing. From the vanishing foil experiment, however, we managed to discover a phenomenon called global separation, where separation happens instantaneously over the entire surface of the body. This global separation allows a more effective and rapid transfer of vorticity, at about one order of magnitude faster than vorticity transfer through conventional means.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Wibawa, Martin Sulaiman

Advisor dc:contributor.advisor

• Michael S. Triantafyllou.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/62791

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/62791