Estimation of Dispersion Coefficients on Free Surface by Means of Particle Simulation Method

The present paper deals with a theoretical treatment of the size effect of solid particles on the estimation of dispersion coefficients at the free surface of flow by means of the tracer simulation method and experimental evidences made at a test flume in the laboratory and a navigation canal. The results obtained through experimentations indicate that the fluctuating velocites of solid particles on the free surface are of outstanding periodicity and therefore the Lagrangian correlation coefficient is not simply expressed in terms of an exponential function as done by Taylor, which must be further investigated by more extensive research programs

Some Features of Turbulent Diffusive Processes in Open Channel Flows

This paper deals with an application of the turbulent diffusion theory by continuous movements of Taylor to the turbulent diffusive processes in open channel flows. It is shown that the mean velocity of the flow can be related to the correlation coefficients of Lagrange by means of the similarity principle of Kolmogoroff and the diffusive characteristics are also estimated by the mean velocity under the condition of constant values in the relative turbulent intensity of uniform flows. The theoretical analysis derived in this paper is also verified through the experimentation made by fine lucite particles and dilute salt water, from a practical point of view. The mechanism of mass transfer, which consists of an essential character in the turbulent diffusive processes, will be still studied

Turbulence Characteristics in Free Surface Shear Flows

The Eulerian and the Lagrangian characteristics of turbulence in a two-dimensional free surface shear flow are investigated both theoretically and experimentally. Using the Kolmogorov's similarity theory, a whole aspect of one-dimensional turbulence energy spectrum can be determined by the two among three fundamental turbulence parameters, that is, the turbulence intensity, the Eulerian integral scale and the energy dissipation rate, and by the kinematic viscosity of fluid. Some turbulence parameters may be expressed in forms of universal function dependent on the relative depth alone, through the Reynolds number similarity. The experimental results of probability distribution show that the Gaussian distribution can not always be applied for the turbulent velocity in a free surface shear flow, and the characteristics of probability distribution may be explained qualitatively by the effect of an intermittent violent motion generated near the channel bed. The power law of -5/3 for the Eulerian spectrum and of -2 for the Lagrangian spectrum are verified through laboratory experiments, and the specific forms of universal function for the turbulence intensity, the Eulerian integral scale and the energy dissipation rate are also determined

Velocity Measurements in a Rectangular Embayment Attached to a Straight Open Channel

わんど内の流れおよびわんど・主流部間の交換を検討するための基礎的実験として, 長方形凸部を有する直線開水路流れにおいて速度計測を行った.その結果, 凸部の開口幅を大きくすることにより交換が促進されること, 水深の条件によって交換機構が全く異なることが明らかにされた他, 凸部が連続した場合には個々の凸部形状が合同であっても交換現象は同一ではなく, 単一の凸部における現象が代表値とはなり得ないことが示唆された.Velocity measurements were carried out in a straight open channel with a rectangular embayment. Two laser Doppler anemometers (LDA) and an electromagnetic current meter (EMC) were employed. Flow exchange between the main flow region and the dead zone, formed within the embayment, is investigated. Turbulent shear region induced at around the junction between the main flow and the dead zone is also studied.Rough sketch of the flow structure drawn from preliminary experiments indicates that large circulating flow is induced in the embayment for the inbank case, however such a circulation cannot be seen for the overbank case. In this case flow exchange between the embayment and its adjacent flood plain takes place in a quite complex manner. Aspect ratio of the embayment also affects the exchange process. For the tested cases arectangular embayment, whose aspect ratio is 3, exchanges more effectively than the square embayment case due to instability of the dominant circulating flow formed in the embayment.わんど内の流れおよびわんど・主流部間の交換を検討するための基礎的実験として,長方形凸部を有する直線開水路流れにおいて速度計測を行った.その結果,凸部の開口幅を大きくすることにより交換が促進されること,水深の条件によって交換機構が全く異なることが明らかにされた他,凸部が連続した場合には個々の凸部形状が合同であっても交換現象は同一ではなく,単一の凸部における現象が代表値とはなり得ないことが示唆された.Velocity measurements were carried out in a straight open channel with a rectangular embayment. Two laser Doppler anemometers (LDA) and an electromagnetic current meter (EMC) were employed. Flow exchange between the main flow region and the dead zone, formed within the embayment, is investigated. Turbulent shear region induced at around the junction between the main flow and the dead zone is also studied.Rough sketch of the flow structure drawn from preliminary experiments indicates that large circulating flow is induced in the embayment for the inbank case, however such a circulation cannot be seen for the overbank case. In this case flow exchange between the embayment and its adjacent flood plain takes place in a quite complex manner. Aspect ratio of the embayment also affects the exchange process. For the tested cases arectangular embayment, whose aspect ratio is 3, exchanges more effectively than the square embayment case due to instability of the dominant circulating flow formed in the embayment

Secondary Flow and Turbulence in a compound Meandering Channel

本報告では, 既報に示された統計理論に基づく複断面蛇行開水路流れの構造を基礎とし, 流速変動の時系列データに乱流解析手法を適用し, 二次流と内部せん断層の組織的構造に関して検討を行った。その結果, エネルギー損失に関する二次流の寄与率が算定されるとともに, 二次流のゆらぎと高水敷・低水路間の流体干渉機構との関連が指摘された.また, 境界部におけるせん断力の発生時に卓越する, 流れの干渉構造が明らかとなった。Secondary flow structure and turbulence characteristics in meandering channels under flooding conditions are discussed. Detailed velocity data measured by a laser Doppler anemometer are used in the analyses. Spectrum analysis is carried out and it shows the contribution of secondary flow to energy dissipation in the whole channel system.Conditional sampling is applied to examine the stress production mechanism. The result shows that a strong shear stress produced at the interface is induced when the lower layer flow is going upward and accelerating along the streamwise direction. Velocity fluctuation also indicates that alternate occurrence of the interfacial shearing and the fluid exchange has close relation to the behaviour of secondary flow cell in the crossover.本報告では,既報に示された統計理論に基づく複断面蛇行開水路流れの構造を基礎とし,流速変動の時系列データに乱流解析手法を適用し,二次流と内部せん断層の組織的構造に関して検討を行った。その結果,エネルギー損失に関する二次流の寄与率が算定されるとともに,二次流のゆらぎと高水敷・低水路間の流体干渉機構との関連が指摘された.また,境界部におけるせん断力の発生時に卓越する,流れの干渉構造が明らかとなった。Secondary flow structure and turbulence characteristics in meandering channels under flooding conditions are discussed. Detailed velocity data measured by a laser Doppler anemometer are used in the analyses. Spectrum analysis is carried out and it shows the contribution of secondary flow to energy dissipation in the whole channel system.Conditional sampling is applied to examine the stress production mechanism. The result shows that a strong shear stress produced at the interface is induced when the lower layer flow is going upward and accelerating along the streamwise direction. Velocity fluctuation also indicates that alternate occurrence of the interfacial shearing and the fluid exchange has close relation to the behaviour of secondary flow cell in the crossover