國立陽明交通大學 機械工程學系Speaker：Dr. Jonathan Tay Chien Ming, National University of Singapore, Department of Mechanical Engineering
Date: 20 September 2018 (Thursday)
Time: 3:30pm – 5:00pm
Venue: 工程五館B1國際會議廳 Engineering Building 5 B1 International Conference Hall
Abstract
For many years, it was thought that the flat hydraulically smooth surface devoid of any surface undulations or roughness would give the lowest flow resistance, or drag compared to all other kinds of surfaces. Anything else would be counterintuitive. Hence attempts were made to make everything from gas pipes and cars to submarines and aeroplanes as smooth as reasonably possible. It was not until only several decades ago, that it was found that a surface could be made to give a drag level lower than that of the smooth flat surface.
By targeting tiny flow structures within the boundary layer, methods were devised to lower the drag below that of the smooth flat surface. This was stunningly demonstrated at the 2008 Olympics when almost all swimming records were broken by swimmers wearing swimsuits incorporating drag reducing riblet technology. A cleverly invented rough surface has demonstrated to offer less flow resistance than a smooth surface in the real world.
Recent studies with shallow circular dimples, or depressions at the surface, have also shown potential for drag reduction. Dimples have the advantage that they are passive, and relatively large and easily manufactured and maintained compared with other drag reducing technologies. The dimple geometry is governed by many geometrical parameters, and studies have shown that many of these have an effect on the drag reducing nature of the dimples. One common observation is that rounded edge shallow dimples with depth to diameter ratios of about 5% or less is required to maximize any observed drag reduction. By careful measurements and study of how the dimples produce drag reduction, the dimple shape can be optimized to maximize the drag reduction of dimples. Studies have been performed with a variety of shapes to understand the nature of the flow over the dimples and how drag reduction can be maximized under various conditions.
About the speaker
Jonathan Tay is currently a Research Fellow at the National University of Singapore (NUS). After receiving B.Eng from the NUS in 2003, he continued working in NUS under various research projects including one sponsored by Airbus on turbulent drag reduction via dimples. He obtained in PhD in 2016, also in NUS and has worked on various projects involving experimental drag reduction and aerodynamic flow control at low and high subsonic speeds. Besides his work in these projects, he has also been involved in teaching and mentoring several student groups in designing and building Unmanned Aerial Vehicles for design projects, workshops and participation in international competitions, including the AIAA Design Build and Fly competitions.
