This paper describes the evolution of surface capillary waves of deep water excited by gradually increasing the lateral external force at a single frequency. The vertical velocities of the water surface are measured b...This paper describes the evolution of surface capillary waves of deep water excited by gradually increasing the lateral external force at a single frequency. The vertical velocities of the water surface are measured by using a Polytec Laser Vibrometer with a thin layer of aluminium powder scattering on the surface to reflect the laser beam. Nonlinear interaction processes result in a stationary Fourier spectrum of the vertical surface velocities （the same as the surface elevation）, i.e. Iω -ω^-3-5. The observed spectrum can be interpreted as a wave-turbulent Kolmogorov spectrum for the case of ‘narrowband pumping＇ for a direct cascade of energy. Correlation dimension analysis of the whole development process reveals four distinct stages during the wave structure development and identifies the wave turbulence stage.展开更多
One mechanism by which laminar flow becomes turbulence is through the instability of vortex interaction.The nonlinear evolution of the interactions between the∧-vortex and the secondary closed vortex has been investi...One mechanism by which laminar flow becomes turbulence is through the instability of vortex interaction.The nonlinear evolution of the interactions between the∧-vortex and the secondary closed vortex has been investigated.This nonlinear instability process leads to some fundamental changes in the topology of flows.Experimental observations are presented here,showing the formation of a chain of ring-like vortices,which generate high frequency spikes on time traces in a transitional boundary layer.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant No 10087101)the National Science Fund for Distinguished Young Scholars (Grant No 10525208)
文摘This paper describes the evolution of surface capillary waves of deep water excited by gradually increasing the lateral external force at a single frequency. The vertical velocities of the water surface are measured by using a Polytec Laser Vibrometer with a thin layer of aluminium powder scattering on the surface to reflect the laser beam. Nonlinear interaction processes result in a stationary Fourier spectrum of the vertical surface velocities （the same as the surface elevation）, i.e. Iω -ω^-3-5. The observed spectrum can be interpreted as a wave-turbulent Kolmogorov spectrum for the case of ‘narrowband pumping＇ for a direct cascade of energy. Correlation dimension analysis of the whole development process reveals four distinct stages during the wave structure development and identifies the wave turbulence stage.
基金Supported by the National Natural Science Foundation of China under Grant No.19972034,and in part by the Isaac Newton Institute for Mathematical Sciences,University of Cambridge.
文摘One mechanism by which laminar flow becomes turbulence is through the instability of vortex interaction.The nonlinear evolution of the interactions between the∧-vortex and the secondary closed vortex has been investigated.This nonlinear instability process leads to some fundamental changes in the topology of flows.Experimental observations are presented here,showing the formation of a chain of ring-like vortices,which generate high frequency spikes on time traces in a transitional boundary layer.
