Aiming To Reduce Environmental Load Via Flow Control

Aiming to Reduce Environmental Load via Flow ControlAt the Fukagata Research Lab at Keio University’s Department of Mechanical Engineering, research is being conducted on fundamental technology to contribute to reducing environmental load via adjustable control of fluid flow.
Specifically, the focus of research is on the reduction of aerodynamic drag through reduction of frictional drag from turbulent flow along surfaces, and on reduction of fluid noise through control of vortices shed from objects.

Aerodynamic drag is broadly divided into pressure drag resulting from the pressure difference of a solid object in a flow, and friction drag that operates on the surfaces of solid objects due to fluid viscosity. For example, for airplanes and bullet trains, half of the total aerodynamic drag or even more is from frictional drag, and it becomes a big cause of energy waste. “As for reducing the pressure drag, as can be seen in the evolution of the nose shape of bullet trains, the drag has been reduced through optimization of this shape, but there has been almost nothing done with regard to reducing the friction drag. So at our research lab we are developing methods to reduce the friction drag in turbulent flows on surfaces through active control that applies some kind of external force to the flow.

A mathematical relationship known as the FIK identity, which was published by Professor Fukagata and others in 2002, is known to exist between the friction drag of turbulent flow and the turbulence stress. Based on this understanding and after undergoing trial and error, by using traveling wave-like wall deformation, the turbulent flow was laminarized. This resulted in a numerical simulation confirming an approximate 70% reduction in the friction drag.

To actually build a traveling wave-like wall would be extremely costly and difficult, so if possible we would like to make this with a fixed wave-like wall, or in other words a non-moving wall, which then resembles optimization of a non-moving shape. Using this we can get a similar drag reduction effect, so this is the type of method we would like to develop.

As for reduction of fluid noise, under joint research with Railway Technical Research Institute, we have attached an active control device called a plasma actuator to a pantograph collector head, which is the power collection unit of the pantograph, and we are conducting wind tunnel experiments to control the vortices shed from the pantograph collector head.

In experiments to date, it has been confirmed that the vortices that are the cause of noise can be almost completely suppressed under a relatively low-speed flow condition. Moving forward, the team would like to verify effectiveness under high-speed flow conditions that correspond to bullet train speeds.

For example regarding aerodynamic drag reduction, even just looking at Japan’s air delivery, if aerodynamic drag could be reduced to half of what it is today, approximately 2 billion liters of fuel could be saved annually, so this could contribute greatly to reducing environmental load. Whether it is reducing aerodynamic drag or flow noise, by following the steps of devising a control method based on logical consideration, using numerical simulation to verify the effect of that control method, and then verifying though use of wind tunnel tests, we want to continue to propose reliable control methods built on theory.