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Mean flow characteristics in a flat and eroded bed curved channel

Sumiadi Sumiadi, Abduh Moh

Journal of Water and Land Development

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2022

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no. 53

170--175

EN

The mean flow characteristics in a curved channel are really different from those in a straight channel. The main cause is the existence of secondary flow within the flow in the curved channel. This paper will discuss the differences in mean flow characteristics due to changes in the bed topography in the curved channel. Acoustic Doppler Velocimetry (ADV) measurements have helped to analyse characteristics of the mean flow on flat and eroded beds in a 180° curved channel. Sand (mean diameter d50 = 0.001 m and specific gravity Gs = 2.65) was selected as the bed material. The condition of flow in the approach section was steady and uniform with 0.159 m depth. One of the mean flow characteristics in the curved channel is the free surface superelevation due to the presence of centrifugal force. The second is the circular motion toward the inner-bank region at the lower layer and toward the upper layer outer-bank region. The cause of the circulation is the difference in centrifugal forces between the two layers. The magnitude of velocity near the bed surface is more significant than the flow near the water surface. This causes erosion in the outer bank region and deposition in the inner bank region. In general, tangential velocity vθ in flat bed is greater than its tangential velocity in eroded bed. The maximum velocity path in a flat and eroded bed of the curved channel resembles a sinusoidal curve, where the minimum value is located at 90° and 120° of the curve.

2

Scour around spur dike in curved channel: a review

Tripathi Ravi Prakash, Pandey Kamlesh Kumar

Acta Geophysica

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2022

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Vol. 70, no 5

2469--2485

EN

A spur dike is a hydraulic structure, protruding in a river or channel used for several purposes like protection of river-bank erosion and deepening of the main channel. The present paper discusses pre-existing research work on flow pattern and prediction of temporal and maximum scours depth around the spur dikes placed in different locations at 90◦ and 180° curved channels. The equations having approximately 2.367, 4.47, 0.17, and 0.271 (average) times with their corresponding experimental data. The parameters, influencing the scour process and flow pattern, have been identified as the ratio of flow intensity to critical velocity (V/Vc≥1) is below 1 and special kind of bedding material is approximately 10 % greater than under livebed condition and many more. The numerical value of the Froude number and the geometry of the bed surface material are also discussed in this paper. Based on these parameters, the empirical formulations and experimental studies on local scours around the straight, L-shaped, T-shaped spurs, placed at 30°, 45°, 60°, 120°, and 180° azimuthal angles have been discussed. Various numerical schemes proposed in almost seventy-five literatures have been summarized. A critical review of numerical and experimental results found in different works related to temporal and maximum scour depth, flow characteristics, and bed topography around the dike shows that the data and accompanying results are insufficient for the design of spurs used as river structures in curved channels. There are needs to carry out extensive experiments, under various flow conditions, to examine the flow behavior and scouring processes around the spurs. Due to complex flow pattern and scouring processes, taking place around the spur, it becomes difficult to understand the real physics behind these phenomenon and therefore, data-driven models are suggested to arrive at more reasonable relationships required to be used for design purposes.

3

Przepływ dwufazowy gaz - ciecz w kanale łukowym

Pietrzyk M., Witczak S.

Inżynieria i Aparatura Chemiczna

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2006

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Nr 6s

192-193

EN

The analysis and test results of hydrodynamics of two-phase gas - liquid flow in a pipe bend is presented in the paper. Types of flow patterns formed in a pipe bend and values of void fractions in phases were determined.