丁坝周围流动图像与局部冲刷深度

Physics of flow and local scour depth around spur dikes

为了研究非淹没丁坝局部冲刷问题,分析丁坝周围流场的实验和数值模拟数据,发现马蹄涡间存在强弱对比和坝头处横向流速占优的现象,提出以5个马蹄涡组成的涡系为主体的流动简化模型,建立丁坝局部冲刷问题的计算模型.计算模型通过考虑垂向流速影响,修正平板绕流解析解,得到适合三维流动的流量计算公式;基于水流连续性和冲刷平衡条件,建立正挑矩形丁坝在清水均匀沙床面情况下最大相对冲深与相对坝长的1/2次方和无量纲流速的1次方的半理论关系,并由现有实验数据确定未知参数值.运用半理论公式得到的计算值与实测数据符合良好,表明流动简化和计算模型合理.

The experimental and numerical simulation data of the flow field around the spur dike were analyzed in order to study the local scouring problem of non-submerged spur dike.There is strong difference in horseshoe vortices＇ strength and the lateral flow velocity dominating at the spur nose.A vortex composed of five horseshoe vortices as the simplified model of flow field were proposed,and a calculation model for local scour depth was established.Revising analytical solution of potential flow past a lateral flat plane by analyzing vertical velocity,a new formula for three dimensional flow rate was obtained.A semi-theoretical relationship of relative local scour depth proportional to the square root of relative spur length and dimensionless velocity was deduced based on the principle of flow continuity and equilibrium scour condition for the situation of 90°rectangular spur on uniform sand bed with clear approaching flow.The coefficient in the semi-theoretical formula was determined by experimental data.The local scour depth calculated by the formula accoroded well with the measured data,indicating that the simplified flow model and the calculation model were reasonable.