Experimental Study On The Flow Structure Downstream Of The Spur Dike

Spur dike is a man-made structure frequently used in controlling the channel evolution or concentrating the flow to flush sediment. Many convex mountains and man-made buildings, such as the bridge prier etc., also influence the flow in many ways similar to spur dike. Therefore, studies on the flow structure around the spur dike are of great significance in improving the flow structure around it and designing the spur dike.In this paper, the instantaneous velocity is measured by the 3D-PDA; the mean flow structure and turbulence behavior are quantitatively analyzed; Based upon these, a new sediment-carrying capacity formula is derived.The general flow field is divided into three sub-regions transversely according to the conservation law of the flow volume: the negative-velocity region of the circulation zone, the positive-velocity region of the circulation zone and the main flow region; In the longitudinal direction, it is divided into two sub-regions: the circulation-increased region and circulation-decreased region.The longitudinal variation of the width of the positive-velocity region and the negative-velocity region is analyzed. It is showed that the normalized width of each transverse sub-region changes linearly along the longitudinal direction in both the circulation-increased region and circulation-decreased region, but the slope of which in each transverse sub-region is different. An inflexion point exists between the circulation-decreased and circulation-increased region.The transverse and vertical turbulence intensity in most regions is increased comparing with that of non-spur dike state but the increasing rate of which is never more then 1.2. Compared with the increasion of longitudinal turbulence intensity, it can be negligible because the increasing rate can reach 1.6,3.0 and 2.0 in the main flow region, the positive flow region and the back flow region. For this reason, the longitudinal variation of the longitudinal turbulence intensity is further studied and the formula of the longitudinal variation of it is derived.A new sediment-carrying capacity equation is derived based on the k-equation. In the new formula, the turbulence intensity can be also considered by considering the formula of the longitudinal variation of the turbulence intensity in each transverse sub-region.From the above, the circulation region is for the first time divided according to the conservation law of flow volume; the distribution of the division lines is quantitatively analyzed; the variation of the turbulence intensity is studied; and finally a new formula of sediment-carrying capacity is derived, in which the turbulence intensity is also considered. It has certain innovation.