Turbulence measurement of a 90-degree flow confluence with the distortion of the shear layer.

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Saiyu Yuan, Hongwu Tang, Chunmei Wang, Xuehan Qiu, Huiming Zhang, Dandan Yu

Thursday 2 july 2015

17:51 - 17:54h at Amazon (level 1)

Themes: (T) Water engineering, (ST) River and coastal engineering, Poster pitches

Parallel session: Poster pitches: 13B. River Engineering

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City channels often have larger aspect ratios given the limited land than natural rivers. The penetration of tributary channel with large flow rate into the main channel causes the distortion of the shear layer. To study the mean and turbulent structure of flow within the distorted shear layer, the authors conducted two cases using different discharge ratios in a discharge-adjusted plexiglass circulating flume. They collected three-dimensional velocities data at six/seven cross sections. Using these measurement data, they analyzed hydraulic and turbulence characteristics, such as mean velocity field, turbulent kinetic energy, Reynolds stress, turbulence spectrum, and occurrence probabilities of quadrant events. They found that two cases had much different characteristics of hydraulic and turbulence characteristics. For the case with the penetration of the larger flow rate of the tributary channel, the stronger helical cell developed in the cross sections and continues for a much longer distance downstream. The region for the highest values of Reynolds stress and occurrence probabilities of ejection and sweep events are more consistent with the shear layer. No obvious energy concentration appeared, and the power law relations for individual velocity components all have exponents which are slightly larger than -5/3 in the flow frequency during spectrum analysis. All these findings might suggest that the sediment transport, bed morphology and pollutant moving be much different between city channel confluences and natural river confluences.