中文摘要：

丁坝坝头绕流呈复杂的三维结构,常导致坝头局部冲刷,易诱发丁坝水毁。为改善丁坝坝头的水流条件,利用四面体透水框架对常规丁坝结构型式作了有益改进,即将常规丁坝的实体坝头改成由四面体透水框架铰接而成的透水坝头,并通过水槽试验研究其水动力特性及冲淤特性。研究表明,透水坝头能有效分散坝头集中绕流,减弱坝头脱离涡的形成条件,并阻滞下潜流,相应地,坝头局部冲刷坑深度也得到有效控制。此外,试验还研究了透水坝头透空率以及长度对局部冲刷的影响。研究发现,存在一个最优透空率,使得透水坝头控制坝头局部冲刷的效果最好,透水坝头的透空率过大或过小时,透水坝头对局部冲刷坑深度的控制有限。另外,在坝头绕流的影响范围内,随着透水坝头长度的增加,其减小坝头局部冲刷的效果越好,当透水坝头长度超过这一范围后,透水坝头长度的增加对减小坝头局部冲刷的效果不再明显。

英文摘要：

The spur dikes are in wide use in the waterway regulation works,however,the emergence of complex three-dimensional flow fields around the groyne head usually leads to the development of a local sour hole which may cause failure of the whole project. In this paper,a novel optimization structure type of the spur dike with permeable groyne head made up of tetrahedron pervious frames is proposed to weaken the flow dynamics at the tip of the spur dike,and a few flume experiments have been conducted in order to study the hydrodynamic characteristics and the scour characteristics of the new structures. Comparing to the conventional ones,significant retardation of the mean velocity and reduction of the velocity gradient are observed while the flow passes through the permeable groyne head. Thus,the concentrated flow in the vicinity of the groyne head is dispersed progressively,the downward-flow at the tip of the spur dike is weakened,and the formation of the shedding vortex is also reduced effectively,resulting in reduction of local scour,which is helpful to the stability of the groyne; in addition,the permeable groyne head is helpful to deflect the flow,and push the local scour hole away from the groyne head,which is also favorable to the stability of the groyne head. The influence of the permeability and the length of the pervious groyne head on the local scour is also studied in this research. Experimental studies indicate that there is an optimal permeability of the permeable groyne head making the local scour control the best; within the scope of the concentrated flow in the vicinity of the groyne head,a longer permeable groyne head means a better effect to control the local scour. However,when the length of the permeable groyne head exceeds this scope,there are no significant effects on the reduction of the local scour as the length of the groyne head increases.