【作者】 于守兵；

【导师】 陈志昌；

【作者基本信息】 南京水利科学研究院 ， 港口、海岸及近海工程， 2010， 博士

【摘要】 工程实践中淹没丁坝是很常见的工况,不同淹没程度△H／H下丁坝对水流结构的调整作用是不同的。实际应用的丁坝具有迎水边坡、背水边坡和端坡,与水槽试验中常见的直立丁坝也有很大不同。采用水槽试验和三维数学模型相结合的方法,主要研究具有迎水边坡和背水边坡的丁坝在非淹没和△H／H=0.17、0.29、0.38和0.44时和相同阻挡面积下端坡系数m=0、3、5和7时水流结构的变化。1)建立基于平面三角形网格和垂向σ坐标系的三维Roe格式浅水紊流模型。推导出σ坐标系下守恒扩散模型。采用计算糙率、水位积分平衡法、三维阶梯流水力模型和部分滑移系数处理丁坝水流模拟中的三维动边界、陡坡、高程间断和边壁阻力问题。考虑边壁阻力的影响能够模拟出非淹没丁坝上、下游小回流区。2)△H／H=0.17时,丁坝下游仍出现回流区；△H／H>0.17时,回流区消失。淹没时坝头附近横向流速较非淹没时减弱,下游回流区内纵向流速分布较非淹没时更为均匀。在受坝体阻挡的纵剖面上,淹没时坝顶的表层纵向流速为1.1～1.7V0(V0为平均流速),在下游出现横轴环流。淹没丁坝对低于坝顶的水流仍起一定的调整作用,这种作用随着△H／H的增加而减弱。坝顶以上和坝头附近的流向偏角和横向流速随着△H／H的增加而减小。m=0时横向水流影响范围bt／L与△H／H呈如下经验关系：bt/L=-5.80△H/H+2.96。3)推导出非淹没和淹没时不同m下丁坝阻挡流量计算公式。考虑端坡对局部水头损失的影响建立非淹没时下游回流区长度计算公式；结合坝顶过流对坝轴断面主流区平均流速的影响建立△H／H较小时丁坝下游回流区长度公式。非淹没时m的增加引起相对回流长度l／L和相对回流宽度b／L的减小。底层平面相对流速V/V0≥1.40和相对底床切应力τb/τb0≥3.00等值线范围随着m的增加明显减小,最大相对底床切应力τbmax／τ0由m=0时的4.40减小至m=7时的3.68。△H／H=0.17时,l/L从m=0时的7.81增至m=1时的9.56,然后随m增加逐渐减小至m=7时为8.16。这种变化趋势与非淹没时的不同。底层平面V／V0≥1.30和τb／τb0≥2.50等值线范围随着m的增加而减小。τbmax/τ0至m=7时已基本稳定为2.90。4)m=0时坝轴断面相对单宽流量q/qin在坝头处明显集中,随着m增大至7时逐渐减小至1.18并与主流区中的趋于一致。坝头从直立到m=3时,端坡的调整作用体现在q/qin=1.35等值线内强度的降低上,但等值线范围未有较大增加甚至缩小。当m>3时,端坡的调整作用体现在q/qin≥1.15等值线范围的减小上。△H／H的增加使得坝顶q/qin增加和主流区q/qin减小,丁坝对水流的调节作用减弱,单宽流量的分布趋于均匀。5)存在端坡时,底层平面V/V0≥1.30和τb/τb0≥2.50等值线范围、τbmax/τb0和q／qin的集中程度等都比坝头直立时大为缩小。另外,端坡的存使得下沉水流和漩涡系不能直接作用于坝头的河床。这些对限制坝头局部冲刷和将更多的流量分配到主流区都是有利的。更多还原

【Abstract】 In projects, especially channel improvement, submerged spur dikes have been widely used. The impact of spur dike on flow structure has changed with overtopping ratio. Spur dikes in engineering normally have upstream slope, downstream slope and head slope, which lead to great difference compared to vertical-wall ones. Flume experiment and 3D mathematical model are used together to study on the impact of head slope coefficient m=0,3,5 and 7 and overtopping ratio△H/H=0.17,0.29,0.38 and 0.44 on local flow structure.1) A 3D shallow water turbulence model with Roe flux format has been established, based on plane unstructured triangle grid and verticalσcoordinate. A conservative diffusion model has been deduced. Computational roughness, water level integral balance method,3D cascade flow hydraulic model and partial slip coefficient are used to solve problems of 3D movable boundary, steep topography, discontinuous elevation and side wall friction simulation, respectively. Consideration of side wall friction is crucial to simulate two small recirculation zones at upstream and downstream near the root of spur dike.2) Downstream recirculation zone has also existed in condition of△H/H=0.17, and disappeared in condition of△H/H>0.17. Transverse flow velocity near spur tip is weaker in submerged condition than in non-submerged condition. In section blocked by submerged spur dike, surface longitudinal velocity is 1.1～1.7V0 (mean velocity), and a downstream horizontal axis circulation occurs.Submerged spur dike has also had adjustment effect in some extent on flow lower than crest, decreasing with increase of△H/H. Deflection angle and transverse flow velocity above crest and next to spur tip have decreased with increase of△H/H. In condition of m=0, a empirical formula between influence extension of transverse flow bt/L and△H/H is as follows:bt/L=-5.80△H/H+2.96.3) A formula has been deduced to compute discharge blocked by spur dike with m in condition of submerged and non-submerged. In consideration of impact of head slope on local head loss, a formula has been proposed to compute downstream recirculation length in condition of non-submerged. And together with impact of overtopping flow on mean velocity in main flume of spur dike axis section, the similar formula has been proposed for small△H/H.In condition of non-submerged, the increase of m has lead to decrease of relative recirculation length l/L and relative recirculation width b/L. The isoline extensions of relative plane velocity V/V0≥1.40 near river bed and relative river bed shear stress have both obviously decreased. The maximum of relative river bed shear stressτbmax/τ0 has decreased from 4.40 at m=0 to 3.68 at m=7.In condition of△H/H=0.17, l/L has increased form 7.81 at m=0 to 9.56 at m=1, and then gradually decreased to 8.16 at m=7, which is different with non-submerged condition. The isoline extensions of river bed plane V/V0≥1.30 andτb/τb0≥2.50 both have decreased with increase of m.τbmax/τ0 has stabilized with 2.90 at m=1.4) Relative unit-width discharge q/qin in spur dike axis section has significantly concentrated at m=0, and has gradually decreased to 1.18, which equals to that in main flume, at m=7. Adjustment effect of head slope has been shown decrease of intension in isoline of q/qin=1.35 from m=0 to m=3, with not obvious increase, even decrease of isoline extension; and decrease of isoline extension of q/qin=1.15 when m>3.The increase of△H/H has brought about increase of q/qin above crest and decrease in main flow zone, weakening adjustment effect by spur dike, and unifying distribution of unit-width discharge.5) The isoline extensions of river bed plane V/V0≥1.30 andτb/τb0≥2.50 and concentration degree ofτbmax/τb0 and q/qin has greatly shrinked with head slope compared to without head slope. In addition, head slope limits down fall flow, and prevents down fall flow and eddy system to directly effect on river bed. All above are beneficial to weaken local scour and transform more discharge to main flume.更多还原