冰盖对层流垂线流速分布的影响研究

Study on the Effects of Ice-Cover on Vertical Velocity Distribution in Laminar Flow

冰盖下的缓慢水流流动可近似为两平行斜板间的层流流动,这为求解冰下层流的垂线流速分布提供了理论基础。采用理论分析的方法对明渠层流及冰下层流的垂线流速分布进行了比较,发现二者的垂线流速分布均可用统一形式的抛物线型公式表示。其中,明渠层流的垂线流速分布可完全确定,冰下层流的垂线流速分布则会因水流纵向压强梯度的不同而不同。同时,冰下层流同一水深处的流速、垂线平均流速、最大流速、单宽流量、流速梯度的最大值均小于明渠层流对应值。结果表明,冰盖通过影响垂线流速分布来影响过水断面的流量,造成流量及输水效率大幅降低,为保证冬季输水渠道的输水效率,应尽力避免冰盖的不利影响。

The slow flow under the ice-cover can be approximated to laminar flow between two parallel inclined plates, which provides a basisfor the theoretical solution of the vertical flow velocity distribution under the ice-cover. In this paper, the vertical velocity distributions of lam-inar flow in open channel and that under ice-cover were studied comparatively by means of theoretical analysis. It was shown that the vertical velocity distribution of laminar flow in open channel and that under ice-cover could be expressed in a unified parabolic form, however, the vertical velocity distribution of the laminar flow in open channel could be completely determined, but which of the laminar flow under ice-cov-er varied with the longitudinal pressure gradient. At the same time, flow velocity in vertical line, the maximum value of vertical velocity, the average value of vertical velocity, the unit discharge and the maximum velocity gradient of laminar flow under ice-cover were all less than the corresponding values of the laminar flow in the open channel. The results show that the ice-cover affects the discharge by affecting the vertical velocity distribution and both the discharge and the water transport rate are greatly reduced. In order to ensure the adequate water supply of water conveyance channels in winter, the adverse effects of ice-cover should be avoided.