基于泥沙异重流稳定性与衰减过程的床面淤积特性研究

Study on bed deposition characteristics based on the stability and decay processes of sediment density current

泥沙异重流在稳定分层和不断衰减的过程中,伴随着床面淤积特征的变化。通过水槽试验观测异重流“稳定-衰减”过程,结合异重分层流运动理论模型,探究该过程对床面淤积特征的影响。研究结果表明,增加异重流层密度或厚度,形成稳定分层形态的时间明显缩短,同时延长了分层形态的维持时间;计算得到的临界雷诺数与扰动波数虚部相应增加,分层形态稳定性得以增强。异重流的稳定行进对于减小床面淤积具有重要作用,试验中临界雷诺数增加568~820,平均淤积厚度降低了42%~46%。因此,提高异重流稳定性并延缓衰减速率,有助于提高输沙率,可以达到减淤的目的。

During the process of the stable stratification and continuous attenuation of sediment density current, it is accompanied by changes in the characteristics of sediment deposition on the bed. Based on the observed process of stable stratification and attenuation of density current in the flume experiment, and combining with the theoretical model of sediment density current movement the influence of the “stability-attenuation” process of density current on the bed deposition has been explored. Research results show that: with the increase of the density or thickness of lower density current, the formation time of stable stratification of density current is significantly shortened, and the maintenance time of stratification is prolonged. Thetheoretical results also show that the critical Reynolds Re_(cr) and the imaginary part of the disturbance wave number α_i increase under these conditions, which indicates that the stability of stratification is enhanced and the stabe movement of density current plays an important role in reducing bed deposition. In the experiment, the critical Reynolds number Re_(cr) increased by 568~820, the average deposition thickness decreased by 42%~46%. Therefore, improving the stability of density flow and delaying the deceleration rate can help improve the sediment transport rate and achieve the goal of reducing sediment deposition.