Kouki Onitsuka

Turbulent structures in partly vegetated open-channel flows with LDA and PI V measurements

The effects of vegetation growing in rivers in and at ihe edge of the water on turbulent structures and the associated sediment transport are not claritied yet. in spite of their importance for hydraulics and river engineering. In this study, turbulence measurements of open-channel flows with a vegetated zone at a half channel width were conducted by making use of both, a laser Doppler anemometer! LDA) and the particle-image velocinietry(PIV). It was found that the intensities of ihe secondary currents and the turbulent energy increase with an increase of the Froude number. The turbulence is adveeted span wisely near the free surface by the secondary currents, which are generated by the anisotropy of turbulence. The horizontal vortices near the free surface are generated by the velocity inflectional instability, which increases w ith an increase of Froude number and the vegetation density. The bed (wall) shear stress in the vegetated zone was calculated by the Reynolds equation with the aid of the empirical drag coefficient.

Prediction of velocity profiles and Reynolds stress distributions in turbulent open-channel flows with adverse pressure gradient

Turbulence measurements in open-channel flows with adverse pressure gradient were conducted with an X-type hot-film anemometer. The velocity profiles in whole depth are described well by the log-wake law which involves a wake strength parameter π. The wake strength parameter π is controlled only by the pressure gradient parameter β in the equilibrium region, i.e., normalized velocity profiles are similar at all streamwise distances. A new relationship formula between the wake strength parameter π and the pressure gradient parameter β is suggested on the basis of experimental data. The equation of motion and continuity equation are transformed to predict the velocity profiles and also the Reynolds stress distributions under the conditions that the flow is in equilibrium and the coefficient of velocity is constant in the streamwise direction. The wake strength parameter π can be predicted with high accuracy from the obtained equations. The predicted Reynolds stress distributions correspond to the experimental data when the pressure gradient parameter β is low. On the other hand, the predicted ones do not correspond to the experimental data when the pressure gradient parameter β is high.

Generation Mechanism of Turbulence-Driven Secondary Currents in Open-Channel Flows

In general, there are two kinds of secondary currents. One is called the ‘secondary currents of Prandtl’s first kind’. The other is called the ‘secondary currents of Prandtl’s second kind’. The vorticity equation is obtained from the equations of motion in the vertical(y) and spanwise(z) directions, as follows:

EFFECTS OF SPANWISE WIDTH OF EXPANSION AREA IN OPEN-CHANNEL FLOW ON RESTING CHARACTERISTICS OF OPSARIICHTHYS PLATYPUS

V\frac{{\partial \Omega }}{{\partial y}} + W\frac{{\partial \Omega }}{{\partial z}} = \frac{{{\partial ^2}}}{{\partial y\partial z}}\left( {\overline {{v^2}} - \overline {{w^2}} } \right) + \left( {\frac{{{\partial ^2}}}{{\partial {z^2}}} - \frac{{{\partial ^2}}}{{\partial {y^2}}}} \right)\overline {vw} + v{\nabla ^2}\Omega

Effects of Transmitted Light and Bubbles in Open-Channel Flows on Fish Behaviors

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Effects of Notch Ratio on Migration Rate in Pool-And-Weir Fishways

\Omega = \frac{{\partial W}}{{\partial y}} - \frac{{\partial V}}{{\partial z}}