CONTROL OF DRAG-REDUCTION BY CHANNEL HEIGHT MODIFICATION -TRANSITIONAL TURBULENT CHARACTERISTICS FROM DRAG-REDUCING FLOW TO TURBULENT FLOW
Department of Mechanical Engineering, Kyoto University Kyoto 606-8501, Japan
Turbomachinery Research Group, Institute for Energy Utilization, National Institute of Advanced Industrial Science and Technology, 1-2 Namiki, Tsukuba, Ibaraki 305-8564, Japan
Mechanical Engineering Laboratory, Ministry of International Trade and Industry, 1-2 Namiki, Tsukuba, Ibaraki 305 Japan
It was proposed to control the drag-reducing flow of a surfactant solution by utilizing the "diameter" effect. Experimental investigation of the proposed method was conducted using a two-dimensional channel.
The turbulent quantities measured by LDV showed that the flow of surfactant solution from "large-diameter" channel experienced a transition from drag-reducing flow to turbulent flow in the "small-diameter" channel. The main velocity profiles varied from drag-reducing "pseudo-laminar" to turbulent in the transition process. The two components of turbulent velocity fluctuation were very small like turbulent drag-reducing flow in the transitional region till x/H2=21.3 at the tested condition, after which they increased dramatically to be dominated by turbulent flow.
Because of the small contracting ratio of the channel, the turbulence produced in the contracted channel was still not completely the same as water flow. Anisotropy of the two components of velocity fluctuations was found, which may explain the destruction process of the rod-like micelles' super structure in drag-reducing flow of the surfactant solution.