風洞水槽による風波の研究(1) ―表面境界層流について―

Abstract

As the first step of the investigation of the wave generation by wind, it was studied experimentally that the development of the wind-driven currentsunder comparatively weak winds. This is the first report of the results.It was found that the current profile was just controlled by the molecular fric-tion. Hence we can call the region of this flow the subsurface boundary layer. Theshearing stresses on water surface were almost in agreement with those calculatedfrom wind profile.The volume transport in the subsurface boundary layer becomes nearly constantsome time later, and then the sharp current profile turns into much more flat onewith large scale eddies. It is understood that the current system, drift currents withslope currents, reaches the steady state. It was shown that this comparatively dis-tinguished transition to the steady state occurred when 7i, t2=constant.In some cases of relatively strong wind in experiments, the slight deviation ofviscosity from molecular one was observed before the steady state was reached. Thischange seemed to occur when the Reynolds numder of subsurface boundary layer flowreached about 420. In these cases, the times when the steady state was reachedwere late a little and were ruled by .rot2=another constant. The change of this con-stant was comparable to that of the viscosity.In one case, it was clearly seen that the above slight change of viscosity wasaccompanied with the waviness of stream lines, though their amplitudes were verysmall. But the sudden growth of surface undulations occurred after a while. Theseare very interesting problems. I will try to clear them continuously.