The Loss of Stability of Laminar Flow in Open Channel and the Mechanism of Sand Ripple Formation
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摘要: 动床水流中,泥沙起动之后,往往要出现沙纹,沙纹成因各家的解释不一。白玉川,罗纪生的观点是:沙纹的尺度较小,主要是由于明渠层流不稳定性波或床面近壁流层中小尺度拟序结构发展演化所致。当床面边界附近扰动波或拟序结构以及水流自身所产生的床面底部切应力大于Shields切应力后,床面即产生响应,形成沙纹;如果扰动所产生的扰动切应力频率接近床面泥沙固有频率,则产生与泥沙颗粒的共振,这种现象也称之为“泥沙的检波性质”,此时床面发生最大响应,沙纹发展速度也最快。Abstract: In the flow on a mobile bed in an open channel,sand ripple often appears after the sediment begins to move.Different scholars have different views on the formation of sand ripples.This paper holds that as the ripple in general is very small,its formation is due to the instability of the laminar flow or the evolution of the small-scale coherent structures in the sub-layer adjacent to the wall of the open channel.When the shear stresses caused by the disturbing waves or the coherent structure near the bed surface boundary and the water flow itself are greater than the shields stresses,responses on the bed surface appear and the sand ripple forms.If the frequency of the shear stress caused by the disturbance is close to the natural frequency of the sand grains that produced resonance,such a phenomenon is called the "detection property" of the sediment.It is at this point that the maximum resonance appears and the sand ripple develops rapidly.
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