Fukuo Ohta

Measurement of ground effect and boundary-layer transition by towing wind tunnel

A newly constructed towing wind tunnel facility is introduced. In this wind tunnel, unlike a conventional wind tunnel, a testing model moves in still air on a testing track. This towing wind tunnel facility can therefore simulate highly complex flow between steady ground and a moving model without using a moving belt system. The performance of this facility is first explained. Some results of wings in ground effect experiments and boundary-layer transition experiments obtained using this facility are then given. From these results, we conclude that this facility has enough performance for complex flow testing.

Measurement of Boundary-Layer Transition by Towing Wind Tunnel

In this paper a newly constructed Towing wind tunnel facility is introduced. This Towing wind tunnel system can create highly complex flow and zero free stream turbulence condition. The performance of this facility is first explained. The results of our first experiment on the boundary layer transition on a flat plate are then given. We concluded that this facility has good performance for complex flow testing under zero freestream turbulence condition.

Development and Interaction of Instabilities in the Crossflow Field

Systematic investigation has been performed to make it clear the three-dimensional(3-D) boundary-layer transition mechanism on a swept cylinder which gives fundamental transition informations for swept main wing of Airbus class aircrafts. Combined use of hot wire anemometer, smoke and liquid crystal film visualizations made it possible to make it clear the quantitative spatial view of the transition process where two instabilities are interacting each other, and the relation between velocity field and heat transfer field. The result shows that the crossflow vortex (stationary primary instability) is important to the turbulent transition process only secondarity in the sense that they deform the 3-D boundary-layer velocity field into inflexional one localy in streamwise direction. This condition directly produces the inflexional instability (traveling secondary instability) which is important primarily to the turbulent transition process while it makes the flow field highly unstable one. Significant aspects in the present investigation is that the transition region where only the primary instability is occuring, is not sensitive to the drag increase, where as it is quite sensitive to the change in heat conductivity rate.

Humidity enclosure process enhanced by streamwise vortices developing over the sea

Abstract To simulate the effect of streamwise vortices on the amount of water vapor entrained to the atmosphere over the sea surface, a wind tunnel experiment was performed. The streamwise vortex structure was visualized over a heated water surface to stimulate the streaky cloud structure over the Sea of Japan in winter. It seems that the existence of vortex structure in the flow tends to enhance the amount of water vapor entrained to the surface air. It is possible that this mechanism is one of the reasons the coastal regions bordering on the Sea of Japan have tremendous amounts of snowfall in winter. Detailed measurements of this flow field are being performed, and the heated solid surface data will be compared with meteorological conditions.