Newsletter  2018.1  Index

Theme : "Mechanical Engineering Congress, 2017 Japan (MECJ-17)" Preface M. MOTOZAWA, S. KUROSAWA Research Progress of Functional Fluids Engineering Hideya NISHIYAMA (Tohoku University) Heat transfer enhancement and drag reducing methods inspired by the skin surfaces of dolphins Yoshimichi HAGIWARA (Kyoto Institute of Technology) On the injection depth of the laser-induced microjet into the soft material Nanami ENDO, Sennosuke KAWAMOTO, Yoshiyuki TAGAWA (Tokyo University of Agriculture and Technology) Cavitation onset induced by sudden acceleration Akihito KIYAMA (Tokyo University of Agriculture and Technology), Zhao Pan (Utah State University), Yoshiyuki TAGAWA (Tokyo University of Agriculture and Technology), Jesse Daily (Naval Undersea Warfare Center), Scott Thomson (Brigham Young University), Randy Hurd, Tadd Truscott (Utah State University) Investigation of the sustaining mechanism of turbulence of Newtonian fluids by using viscoelastic fluids Yasufumi HORIMOTO, Susumu GOTO (Osaka University)

 

Heat transfer enhancement and drag reducing methods inspired by the skin surfaces of dolphins

Yoshimichi HAGIWARA Kyoto Institute of Technology

Abstract

Bio-inspired engineering has been focused recently. As one of the typical examples of this new idea, we have focused on new techniques concerning friction drag reduction, inspired with the soft, folded skins of fast-swimming dolphins.

We conducted measurements on velocity field over wavy plates on the bottom of an open channel by using flow visualization and image processing techniques.As one of the typical examples of this new idea, we have focused on the techniques of friction drag reduction inspired with the soft, folded skins of fast-swimming dolphins. We conducted measurements on velocity field over wavy plates, which were inspired with the fold skins, on the bottom of an open channel by using flow visualization and image processing techniques. In addition, we measured the total drag acting on the wavy plates by detecting the strain of cantilevers, which supported the test plates. It was found that the reductions of friction drag and increases in the pressure drag were obtained by the wavy plates. To apply this kind of wavy surface to heat exchangers, we carried out direct numerical simulation on turbulent flow and heat transfer between two wavy walls. The computational results showed a decrease in the wall shear stress and an increase in the Nusselt number compared with the results for a flat wall. The decrease in the wall shear stress was caused by a decrease in the production of turbulent kinetic energy due to decreases in the Reynolds shear stress and velocity gradient. The increase in the Nusselt number was a result of a decrease in the mean temperature. This decrease was a result of a decrease in the mean temperature gradient, which was caused by a noticeable increase in the turbulent heat flux. All the results showed the breakdown of the Reynolds analogy in the developed turbulent channel flow.

Finally, the challenging strategy of frontier fluids engineering in the future is proposed for the young scientists and engineers.

 

Key words

Bio-inspiration, Dolphin, Skin fold, Drag reduction, Heat transfer enhancement

 

Figures

Figure 1 Top view of a test plate (unit: mm)


Figure 2 System for the total drag measurement


Figure 3 Domain for direct numerical simulation


Figure 4 Simulation result for shear stresses