Seminar Series

PG Talks: Reducing Drag for Separated Flows by Passive Suction/Blowing Control


PhD Candidate James Ramsay


Department of Mechanical Engineering, University of Canterbury

Time & Place

Thu, 26 Nov 2020 14:40:00 NZDT in E14, Engineering Core


In New Zealand, almost 9% of our total greenhouse gas emissions are attributable to the energy burned by cars and trucks to overcome aerodynamic drag. Drag is the force that fluids (like air or water) impart on bodies moving through them, and since the Earth is 70% covered in water and 100% covered in air it affects nearly every engineering problem. The traditional method for reducing drag and its impact has been to streamline objects – to change their shape to be smooth and slender. However, this is not possible in many applications – for example for cargo trucks. An alternative method to reduce drag – and one that can have dramatic impact – is to suck a small amount of fluid through the wall of the body. This helps the rest of the fluid to flow more easily around the body and alters the pressure profile reducing the drag. My PhD project – supervised by Mathieu Sellier (UC) and Wei Hua Ho (WITS) – has investigated what the optimal suction control of separated flows (flows with eddies forming near walls) is under different conditions, and whether this control can be implemented passively. We focused specifically on the circular cylinder as the representative for external flows (the least streamlined smooth body out there), and the expanding pipe for internal flows. If we can avoid the use of pumps to drive this suction, we can generate completely efficient aerodynamic bodies with a modern form of flow control. This is theoretically possible but has been challenging to make a reality. This talk will outline the work of this PhD towards this goal.

PG Talks, James Ramsay

Supervisor: Prof Mathieu Sellier