船型浮堤布置形式对水流结构影响数值分析

Numerical Study on the Flow Characteristics Around Ship-shaped Floating-dike with Different Layout-forms

摘要

船型浮堤相比于丁坝，具有缓流促淤、生态适宜特点，但将船型浮堤应用于河道整治尚缺乏足够理论支持。为进一步揭示船型浮堤对水流结构的影响，采用k‒ε模型（k为湍动能）研究船型浮堤淹没比例D（即吃水深度∶水深）、长度比例K（即船长∶河宽）、布置角度θ（θ>0时下挑）与床面横向坡度对船型浮堤三维水流特性与湍动能分布的影响，并利用水槽试验验证。结果表明：1）随着D从0.2增至0.8，船型浮堤下方最大相对纵向流速（即U/U_0max，U为局部最大流速，U_0max为入口平均流速）增加，回流长度与U/U_0max分别从1.0L（L为船长）增至3.5L、从-0.35增至-0.51，船型浮堤后方湍流强度随D增加而增大。2）随着K增加，船型浮堤下方与外侧流速增加，回流区与缓流区范围增大，但回流区长度与回流强度保持不变，湍动能强度增强并在船型浮堤底部与后方形成核心区。3）船型浮堤向上挑（θ=-30º）时阻水作用明显，近岸处其上游U/U_0max衰减至0.4，底部U/U_0max（1.53）小于θ为30º时的U/U_0max（1.63）；船型浮堤后方缓流区分布范围在下挑时大于上挑，下挑时水流流态平稳，湍动能较弱并在船型浮堤后方形成局部加速区与环流。4）当船型浮堤布置于深水侧时，水流集中在船型浮堤下方，回流区强度增加，河床横向坡度使船型浮堤后方环流增强。上述研究结果表明：船型浮堤缓流促淤效果在其布置于深水侧、向下挑、淹没比例\le0.4、长度比例\le0.5时最好，船型浮堤后方缓流区稳定、环流发育、对底部流场扰动小，具有生态适宜性。研究结果为实际河流整治工程提供了技术支持与参考。

Abstract

Objective A spur dike is an in-stream structure that is widely employed for the protection of riverbank erosion. In river engineering, traditional regulating structures exhibit certain limitations, such as occupying large areas, requiring significant quantities of stone, being difficult to maintain, and involving high construction costs, which make them unsuitable for use in some regions. Therefore, scholars propose the application of floating dike structures in river regulation engineering. These structures exhibit advantages such as minimal impact on sediment transport, improved adaptability to upstream water and sediment discharge, and reduced impact on the riverbed and ecological environment. However, research on the effects of floating dikes on flow structure and the riverbed remains insufficient, and the understanding of their practical application is limited. Considering practical application, ships are used as substitutes for floating dikes; therefore, this structure is also referred to as a ship-shaped floating dike. This study focuses on the effects of the submergence ratio (D is submergence depth/water depth), length ratio (K is ship length/river width), arrangement angle (θ > 0 indicates the dike oriented downstream), and transverse bed slope at the location of the ship-shaped floating dike on the surrounding flow field and turbulence characteristics. The findings provide a hydrodynamic basis for further understanding the influence of ship-shaped floating dikes on sediment transport and riverbed evolution, as well as technical support and reference for their application in practical river engineering projects. Methods This study investigated the influence of geometric characteristics, including submergence depth and ship length, as well as arrangement parameters, including ship angle and transverse bed slope, of ship-shaped floating dikes on the surrounding flow field and turbulence structure, with the objective of identifying the optimal arrangement configuration. The same flume dimensions (length is 1.4 m, width is 0.3 m, and height is 0.05 m) and simulation conditions as those used in the physical model experiments were adopted to enhance the reliability of the numerical model. The RNG k‒ε turbulence model was employed to simulate the flow structure around the ship-shaped floating dike. Considering the negligible variation in the water surface, the rigid-lid assumption was applied, with a constant inlet velocity and free outflow conditions at the outlet. The velocity-pressure coupling equations were solved using the semi-implicit SIMPLE algorithm. Results and Discussions The numerical simulation results for velocity distribution and Reynolds shear stress across different longitudinal sections were consistent with those obtained from physical experiments, confirming the reliability of the numerical model. The three-dimensional flow structure and turbulence kinetic energy distribution were analyzed by considering variations in the submergence ratio (D), length ratio (K), arrangement angle (θ), and transverse bed slope (S_L) of the ship-shaped floating dike. The numerical results were verified against experimental observations. The results demonstrated that: 1) As D increased from 0.2 to 0.8, the maximum relative streamwise velocity below the ship-shaped floating-dike (SSFD), defined as the ratio of local maximum flow velocity/inlet average flow velocity (U/U_0max), gradually increased, from 1.52 to 1.69. The length of the back-flow area and U/U_0max increased from 1.0L to 3.5L (L is the length of SSFD) and from ‒0.35 to ‒0.51. Increasing D also intensified near-bed flow velocity and enhanced turbulence intensity downstream of the SSFD. 2) As K increased, the effective flow-passed cross-section decreased, resulting in increased flow velocity below and outside the SSFD. The area of the back-flow and low-velocity zones expanded with increasing K, whereas the length and intensity of the back-flow region remained nearly unchanged. Turbulence kinetic energy gradually increased and formed a concentrated core region near the bottom and downstream of the SSFD. 3) When the SSFD was tilted upward with θ = ‒30º, a strong blocking effect was observed, with U/U_0max upstream of the SSFD reduced to 0.4, while near the shore and bottom of the SSFD, U/U_0max = 1.53, which was less than θ = 30º with U/U_0max = 1.63, but both were less than θ=0 with U/U_0max = 1.72. The distribution of the slow-flow zone behind the SSFD was larger when θ = ‒30º. When θ = 30º, the flow remained relatively stable, characterized by weak turbulence kinetic energy, and localized acceleration zones and circulation structures developed downstream of the SSFD. When the SSFD was positioned on the deeper side of the channel, the flow concentrated beneath the structure, resulting in an intensified back-flow region. The transverse slope of the riverbed enhanced downstream circulation. The results indicated that the SSFD achieved optimal slow-flow and sedimentation promotion effects when it was arranged on the deeper side, tilted downward, with a submergence ratio \le 0.4 and a length ratio \le 0.5. Conclusions The geometric dimensions and spatial arrangement of the ship-shaped floating dike, along with the transverse bed slope, play a significant role in influencing the surrounding hydrodynamic characteristics and turbulence structure. As an innovative river regulation structure, the ship-shaped floating dike exhibits advantages including the formation of a stable slow-flow zone downstream of the dike, well-developed secondary circulation, and minimal disturbance to the bottom flow field, which collectively contribute to favorable ecological compatibility. These findings provide valuable technical support and practical reference for the application of ship-shaped floating dikes in river regulation engineering projects.

Graphical abstract

关键词

船型浮堤 / 水动力结构 / 河流整治 / 数值模拟

Key words

ship-shaped floating-dikes / hydrodynamic structure / river regulation / numerical simulation

本刊网刊

“十四五”

在河流与航道整治中，丁坝是使用最为广泛的整治建筑物。丁坝可以保持河流或航道所需水深，使主流偏转防止水流冲刷破坏，减小对河岸的侵蚀^[1‒2]并改善水生生物栖息地环境^[3‒5]。当水流经过丁坝时，在丁坝上游出现三维水流分离并在丁坝下游出现马蹄涡，复杂的流态促进冲刷坑发育^[6‒7]，水流不稳定会产生不利的流态与河势，影响河流的稳定与整治工程的安全^[8]。丁坝影响区域内的泥沙输移与水流结构、湍流相关，冲刷区域和冲刷坑发育与床面形态密切相关^[9‒11]。

传统航道整治建筑物侧重于整治工程效果而在一定程度上忽略了对河流生态的影响。传统的护岸和丁坝利用水泥、砂浆、混凝土等作为主要建筑材料，形成封闭的结构，阻隔了上下游水流与生态系统物质与能量交换，破坏了生境。为改善底栖生物群落生存环境，研究者提出了透空型丁坝形式^[12]，研究了梯形透空丁坝局部冲淤演变^[13‒14]、泥沙输移特征^[15‒16]及其对底栖生物群落、鱼类活动的影响^[17‒18]。Wan等^[19]对长江重庆段的生态丁坝的水流特征与浮游生物群落进行了研究，结果表明，丁坝下游浮游生物多样性高于上游，这与丁坝下游处溶解氧显著增加，水体浊度与流速显著降低有关。相比固定于河床上的整治建筑物，Huang^[20]和黄卫^[21]等认为浮在水面上的结构（如浮堤与浮筏）具有对河流泥沙输移影响较小、更好适应上游来水来沙、对河床与生态环境影响较小等优势。浮堤结构常见于水电站拦污导漂^[22‒23]、泵站进水口不良流态整治^[24]、海岸浮式防波堤消浪^[25‒27]等。目前，将浮堤结构应用于河道整治的研究较少，缺乏浮堤对水流与泥沙运动作用机理的研究。

在实际应用中可将小型船舶充当浮堤结构，这种结构称为船型浮堤。本文针对浮堤的布置形式对水流结构与湍流特征的影响开展数值模拟研究，利用黄卫等^[21]的浮堤局部三维水流特性试验结果进行验证。以往对丁坝的研究围绕丁坝的几何形状、河床泥沙特性与上游来流条件对丁坝周围水流结构与冲刷模式^[28]的影响，本文从船型浮堤几何尺寸（船体长度、吃水深度）与布置形式（挑角、岸边水深）方面分析船型浮堤对水流结构的影响，探究船型浮堤的保护岸滩的效果与生态适宜性。

1 工况说明与模型建立

整治工程对水流结构影响的数值模拟模型包含RNG k‒ε模型^[29‒30]、雷诺应力模型^[31]和大涡模拟模型^[4,32]。魏文礼等^[33]采用RNG k‒ε模型对弯道内布设丁坝后的水流结构进行了数值模拟分析。RNG k‒ε模型在大尺度运动中体现出小尺度运动影响，常用于模拟高应变率及流线弯曲较大的流动，具有较高的稳定性和计算精度。RNG k‒ε模型的动量方程与湍动能、湍动能耗散率方程分别如式（1）～（3）所示^[34‒35]：

\begin{array}{c}\frac{\partial (\rho u_i)}{\partial t}+\frac{\partial (\rho u_j{u}_i)}{\partial x_j}=-\frac{\partial p}{\partial x_i}+\\ \frac{\partial }{\partial x_j}\left((\mu +{\mu }_{\mathrm{t}})\left(\frac{\partial u_i}{\partial x_j}+\frac{\partial u_j}{\partial x_i}\right)\right)+\rho g_i\end{array}（1）

\frac{\partial (\rho k)}{\partial t}+\frac{\partial (\rho u_{j}k)}{\partial x_j}=\frac{\partial }{\partial x_j}\left(\left(\mu +\frac{{\mu }_{\mathrm{t}}}{{\sigma }_k}\right)\frac{\partial k}{\partial x_j}\right)+\rho G-\rho \epsilon（2）

\begin{array}{c}\frac{\partial (\rho \epsilon )}{\partial t}+\frac{\partial (\rho u_j\epsilon )}{\partial x_j}=\frac{\partial }{\partial x_j}\left(\left(\mu +\frac{{\mu }_{\mathrm{t}}}{{\sigma }_{\epsilon }}\right)\frac{\partial \epsilon }{\partial x_j}\right)+\\ \rho \frac{\epsilon }{k}(C_{\mathrm{1}\epsilon }^{\mathrm{*}}G-C_{\mathrm{2}\epsilon }\epsilon )\end{array}（3）

式（1）～（3）中：x_i 、x_j 分别为水流在i、j方向坐标，m；u_i 、u_j 为流速在i、j方向上的速度分量，m/s；p为压力，Pa；ρ为密度，kg/m³；g_i 为在i方向上重力加速度分量，m/s²；ε为湍流耗散率，m²/s³；k为湍动能，m²/s²；μ_t为湍流黏性系数，μ_t=ρC_μk²/ε，Pa·s；C_μ、{\sigma }_k、{\sigma }_{\epsilon }、C_{\mathrm{2}\epsilon }均为经验系数，C_μ =0.085，{\sigma }_k=1.0，{\sigma }_{\epsilon }=0.717 9，C_{\mathrm{2}\epsilon }=1.68；μ为分子黏性系数，Pa·s；G为湍动能产生项，G=\frac{{\mu }_{\mathrm{t}}\partial u_i}{\rho \partial x_j}\left(\frac{\partial u_i}{\partial x_j}+\frac{\partial u_j}{\partial x_i}\right)，m²/s³；C_{\mathrm{1}\epsilon }^{\mathrm{*}}为与μ相关的函数。

利用粒子图像测速法（PIV）可获得精细的流场结构^[36]，黄卫等^[21]通过水槽试验，利用高分辨率PIV系统测量浮堤周围局部三维水流特性。为增加研究成果的可靠性，本文构建的数值模型与黄卫等^[21]的物理试验模型相同。本次模拟区域长1.40 m，宽0.30 m，深0.05 m，底部坡降0.001，船型浮堤布置于左岸（X=0，Y=0，Z=0.50 m，X为水流方向坐标，Y为横向坐标，Z为垂向坐标，底部Z=0），区域平面图如图1所示。表1为本次数值模拟工况，W为河宽，h₀为水深，分析船型浮堤的几何尺寸（长度L、淹没深度d）、布置角度θ（上挑为-，下挑为+）与横向坡度S_L（船型浮堤处水深小于对岸为负）对水流结构的影响。本次模拟工况1～6与黄卫等^[21]试验工况1～6相同；所有工况边界条件保持一致，入口处水流为恒定流，水深h₀为0.05 m，断面平均流速U₀为0.19 m/s，入口处雷诺数R_e为9 405.94，Froude数F_r为0.27；出口处为自由出流，水槽固体壁面与船型浮堤为无滑移边界，采用标准壁面函数处理。所有工况在船型浮堤处网格加密（最小网格尺度为1 mm），总网格数在1 500万网格以上。考虑到模拟工况的F_r较低，对于水面可采用刚盖假定^[4]，即水面假定为一个无切应力的平面。计算过程采用RNG k‒ε模型，速度与压力的耦合方程采用半隐式SIMPLE算法求解，离散格式中对流项、扩散项与源项采用二阶迎风格式，采用并行计算，计算过程使用天玑算（www.phadcalc.com）平台，算力配置如下：CPU型号为64核EPYC 7H12，主频为2.6 GHz。

2 模型结果与试验结果对比

为提高本次数值模拟结果可靠性，将本文工况2的模拟结果与Huang等^[20]进行的物理模型试验结果在纵向流速U与横向雷诺切应力R_s分布方面进行对比。附录A图A1为工况2中U在Y为5.0、7.5、15.0 cm纵剖面上的分布（附录A图A1（a）、（c）、（e）），以及物理模型PIV测量结果（附录A图A1（b）、（d）、（f））。由结果可知：水流经过船型浮堤时，近表面水流受到船型浮堤的阻挡向另一侧流动，另一部分水体经过船型浮堤下方时在船型浮堤下方出现水流分离区，其后方U增加至0.25 m/s，在Y为1/2L近底处U增加至0.29 m/s，在Y为15.0 cm处由于船型浮堤减小过流断面，U为0.26 m/s。船型浮堤后方回流范围与流速达到最大，回流长度>L，最大回流流速为-0.08 m/s，为0.42U₀；在Y=7.5 cm处回流范围与强度减小，回流中心向船型浮堤移动。以上结果与Huang等^[20]分析结果相符。

附录A图A2为工况2中各纵剖面上横向雷诺切应力R_s的对比结果。可知：在船型浮堤下方R_s<0，R_s达到-0.37 Pa；在船型浮堤后方R_s增大，在距离边壁7.5～10.0 cm处，R_s从1.5 Pa衰减至1.1 Pa。在远离边壁处（Y为12.5 cm），R_s强度和范围逐渐减小，模拟结果与试验结果基本相符。横向雷诺切应力分布表明，船型浮堤对流场的扰动影响集中于船型浮堤下侧及距离船型浮堤后方L处以内。

3 船型浮堤布置对水流结果影响

不同的船型浮堤布置对水流的扰动结果不同，Huang等^[20]的分析结果受PIV观测区域限制无法分析平面上的流场分布。本文补充分析了船型浮堤吃水深度、长度、角度以及河床横向坡度对流场结构的影响，围绕纵向流速U、横向流速V及湍动能k进行分析。

3.1 船型浮堤吃水深度影响

图2中为不同船型浮堤淹没比例D下典型纵剖面上相对纵向流速U/U₀分布结果。由图2可知：随着D从0.2增加至1.0，底部U/U₀最大值U/U_0max在D为0.2、0.4、0.8时分别为1.35、1.52、1.69，船型浮堤后方回流长度分别为1.0L、1.5L、3.5L，回流区U/U_0max分别为-0.35、-0.48、-0.51，即船型浮堤后方回流区域的强度与范围随着淹没比例的增加而增加。在Y为12.5 cm处，船型浮堤处U/U₀随着D的增加而增加；在船型浮堤后方，U/U₀随D增加呈现先增加后减小趋势，与不同淹没比例下回流分布范围有关。

图3中为各横剖面上不同淹没比例（工况2、3、4、7）下U/U₀分布。由图3可知：在近水面（η=(h₀－Z)/h₀=0，η为归一化水深），船型浮堤外侧U/U₀随D增大而增大，回流分布随D增大向对岸与船型浮堤后方扩散。当D≠1时，船型浮堤后方回流中心靠近船型浮堤边缘处；当D\ge0.8时，船型浮堤后方形成两处回流中心，随着D增大，靠近船型浮堤的回流中心向岸边移动，在下游的回流中心流速增大。在船型浮堤下方的床面处（η≈1），当D为0.2～0.4时，仅在船型浮堤处形成局部加速，对船型浮堤后方流场影响较小；当D为0.8～1.0时，船型浮堤上游回流强度增加，即U/U₀从-0.11变至-0.45，船型浮堤在D=0.8时，底部U/U_0max=1.70，在距离船型浮堤下游6L处，回流强度增加至-0.89U₀。随着D增加，船型浮堤对底部流场的影响越大，在船型浮堤下方与外侧纵向流速增大，船型浮堤后方的回流中心在D≠1时分布在船型浮堤边缘处，在D\ge0.8时，在距船型浮堤后方6L处形成第2个回流中心且在近床面处占主导。

附录A图A3为各纵剖面上不同淹没比例下相对湍动能TKE（记为K_E，K_E=k/u_{\mathrm{*}}^{\mathrm{2}}，u_*为摩阻流速，u_*=\sqrt[]{gRJ}，g为重力加速度，R为水力半径，J为底部坡降）分布。当D≠1时，Y=5 cm时，船型浮堤下方，TKE在D为0.2、0.4、0.8时，分别为17.9、21.6、32.9。随着船型浮堤下方过水断面减小，TKE增加，增加了水流对河床的侵蚀强度。随着D增加，TKE核心区增大，且分布在距船型浮堤2L内。Y=9.5 cm处TKE减弱，分布范围缩小。Y=12.5 cm处，当D\le0.4时，船型浮堤对TKE影响较弱；当D=0.8时，TKE\ge10的分布范围扩大；当D=1时，在船型浮堤所在处，TKE达到峰值，在5L～6L形成第2处TKE核心区。从减小船型浮堤造成的不良流态及湍流强度分布方面考虑，船型浮堤的淹没比例不应超过0.8，船型浮堤附近的湍流强度随着D的增大而显著增加。

3.2 船型浮堤长度影响

图4为典型纵剖面不同长度比例K（工况2、5、6）下U/U₀分布。由图4可知，随着船型浮堤K增加，船型浮堤下方与外侧的U/U₀增加。当Y=1/2L时，船型浮堤底部U/U_0max在K为1/6、1/3、1/2时，分别为1.33、1.49、1.73，底部流速加速区范围随着K的增加而增加，回流区U/U_0max分别为-0.40、-0.41、-0.46，船型浮堤长度对底部过流区的影响大于后方回流区，回流区长度与船型浮堤长度一致。在Y=L处，回流区减弱，随着K增加，船型浮堤后方U/U₀增加，容易将船型浮堤底部泥沙挟带至后方落淤。在Y=1.5L处，船型浮堤后方U/U₀随K的增加而增加。

图5为典型横剖面上不同长度比例下U/U₀分布。由图5可知，在横剖面上，在近水面处，回流区随K增大而增加，回流区强度与长度并未增加。船型浮堤后方缓流区随着K增加向水槽中央扩展，在船型浮堤边缘形成最大流速区，U/U_0max随着K增大而增大，如K为1/6、1/3、1/2时，U/U_0max分别为1.40、1.50、1.71。在船型浮堤下方，回流区强度衰减，船型浮堤后方缓流区与外侧主流区保持不变。在近床面处，船型浮堤下方存在局部加速区，在K\ge1/3时，随着K增加，近床处加速区强度逐渐增强。

从各纵剖面上船型浮堤不同长度比例下TKE分布可知（附录A图A4），在距离边壁Y=1/2L处，TKE强度与分布范围随K增加而增加，在船型浮堤底部与后方形成核心区，TKE最大值在K为1/6、1/3、1/2时分别为17.4、17.2、21.7。在船型浮堤边缘处、船型浮堤底部形成TKE核心区，TKE强度与分布区域减小。在Y=1.5L处，船型浮堤对TKE没有影响。

3.3 船型浮堤挑角影响

图6显示了船型浮堤与水流垂直（θ=0，即工况6）、上挑（θ=-30°，即工况8）与下挑（θ=30°，即工况9）3种布置形式对水动力结构与湍流结构的影响。由图6可知：相比于θ为0，θ为-30°时靠近岸壁处（Y=1/6L）船型浮堤的阻水作用明显，水流在船型浮堤上游减速明显（U/U₀=0.4），此时在船型浮堤底部U/U_0max（1.53）小于θ为0时U/U_0max（1.72），船型浮堤后方回流区域向底部扩散，水流紊乱。当θ为30°时，船型浮堤底部U/U_0max为1.63，回流区U/U_0max（-0.29）小于θ为0时U/U_0max（-0.4），在距离船型浮堤L处近水面，U/U₀形成局部加速区，其与船型浮堤后方形成的环流相关。在Y=1/2L处，当θ为-30°时船型浮堤底部高流速区扩大，回流区强度减小；当θ为30°时，船型浮堤后方回流区扩大，环流减弱。在Y=L处，当θ为-30°时船型浮堤对流场的扰动大于θ为30°时。综上可知：当船型浮堤向上挑时，对流场的影响作用较强，近岸处流态紊乱，船型浮堤外侧流速增强；当船型浮堤向下挑时，船型浮堤后方环流作用增强，水流流态平稳。

图7为不同挑角下典型横剖面上U/U₀分布。由图7可知：相比于θ为0时的情况，当θ为-30°时，船型浮堤上游缓流区扩大，后方回流区显著减小，回流范围从近表面到船型浮堤下侧逐渐增大，船型浮堤后方高流速区侵入缓流区。当θ为30°时，流场特征与θ为-30°时相反，船型浮堤后方缓流区稳定性增加，在近岸处形成加速区，加速区在船型浮堤下方达到最强。近床面处，不同挑角布置对底部流场影响较小，在船型浮堤下方形成局部加速区。上述流场分布表明，当船型浮堤布置为向下挑时，船型浮堤后方的环流作用达到最强，且在近岸处形成局部加速区。

附录A图A5为不同挑角下典型纵剖面相对湍动能分布。由附图5可知：当θ为-30°时，近壁处的湍动能分布散乱，TKE最大值（记为K_Emax）为10.3，小于θ为0时的K_Emax（19.6）；在距离边壁Y=1/2L处，TKE向水面扩散。当θ为30°时，近壁处TKE在船型浮堤处下方形成核心区，K_Emax为19.8，在船型浮堤后方TKE核心区向水面扩散，TKE强度弱于θ为0时，在Y=1/2L处TKE向底部扩散。综上，当船型浮堤呈现上挑或下挑时水流的湍动能明显弱于与水流垂直布置时，当θ为30°时近岸处环流强度较强使TKE向水面扩散。

3.4 横向河床坡度影响

在实际应用中，河床往往存在横向坡度S_L，将船型浮堤布置在横断面上深水侧与浅水侧对流场结构影响不同。将工况10（S_L=-0.1）与工况11（S_L=0.1）、工况9（S_L=0）进行对比，图8为工况9～11在典型纵剖面上U/U₀分布结果。由图8可知：在Y为1/6L处，S_L为-0.1时，船型浮堤处水深较浅，船型浮堤底部过流减少，U/U_0max为1.58，在船型浮堤后方形成回流区与缓流区，U/U₀分布与图2（c）相似（工况4）。在S_L为0.1时，船型浮堤处水深增大，水流集中在深水区，在其下方形成高流速区，U/U_0max为1.61，略小于S_L为0时的U/U_0max（1.63）；在船型浮堤后方，回流区分布保持不变，其U/U_0max为-0.36，强度略大于S_L为0与-0.1的U/U_0max（分别为-0.29、-0.22）。在Y=1/6L处，船型浮堤后方的缓流区范围（U/U₀<1）在S_L\ge0时缩小，并出现增速区（U/U₀>1）。当Y=1/2L时，船型浮堤后方的回流区增大，回流强度基本保持不变，随着S_L从-0.1增至0.1，船型浮堤底部U/U_0max逐渐增强。

图9为典型横剖面上不同S_L下U/U₀分布。由图9可知，在近水面处，S_L对流场分布影响较小，缓流区能保持较长范围的稳定。当S_L\ge0时，缓流区近壁侧出现增速区，且随着S_L增大而加强，在η=D处增速区达到最大。θ=30°时，船型浮堤对水流的阻碍作用较小，在船型浮堤后方形成环流使得船型浮堤下方高流速水流向边壁输移，S_L>0时环流强度增强。当η=1时，工况10中，水流聚集在对岸深水区，在船型浮堤所在处形成加速；工况9中，仅在船型浮堤下方形成加速区；工况11中，船型浮堤下方形成高流速区，靠近床面的水流分布验证了在船型浮堤淹没范围内缓流区内出现增速区是受环流影响的结果。

附录A图A6为不同河床横向坡度下各纵剖面上湍动能分布。由附录A图A6可知：当S_L=-0.1时，TKE核心区与底部平行；当S_L\ge0时，船型浮堤后方TKE向水面扩散并逐渐衰减。在Y=1/2L处：当S_L=-0.1时，TKE分布范围小于当S_L\ge0时的范围；当S_L=-0.1时，TKE向床面扩散，表明靠近边壁与远离边壁处水流紊动受到环流的影响。在Y=L处，工况9～11的TKE分布相同，表明TKE仅受到船型浮堤导致过流断面减小的影响。

取不同横断面上相对横向流速（V/U₀）分析船型浮堤后方二次环流分布，结果如附录A图A7所示。由附录A图A7可知：在X=0时，Y=0处受到船型浮堤阻挡，水流向对岸流动；在X=0.1 m处形成环流，底部V/U_0max位于区间[-0.31,-0.32]，随着S_L从-0.1增加至0.1，近水面处V/U_0max从0.49增至0.60，二次环流在船型浮堤外侧消失；当X为0.15～0.25 m，在S_L=-0.1时，环流强度衰减速度远大于S_L\ge0时的衰减速度，船型浮堤后方环流分布从机理上解释了缓流区以及近壁处增速区分布，也说明了船型浮堤的缓流促淤的工程效果。

4 结 论

本文对船型浮堤的几何尺度、挑角与底床横向坡度对水流动力结构与湍动能分布的影响进行了数值模拟，模拟结果与水槽试验结果较为吻合。本文的主要结论为：

1）随着淹没比例（D）增加，船型浮堤底部最大相对纵向流速（U/U_0max）从1.35增加至1.69，船型浮堤后方回流区中心紧靠船型浮堤，回流范围与强度增加；当D\ge0.8时，在船型浮堤下游形成第2个回流中心；当D≠1时，船型浮堤底部与外侧过流区湍动能随着D增大而增加。

2）随着长度比例（K）增加，船型浮堤下方与外侧U/U_0max增大，湍动能强度与分布范围增大，回流区相对长度与强度变化不大，当K\ge1/3时近床处船型浮堤下方流速显著增加。

3）当船型浮堤向上挑时，对流场的影响作用较强，阻水作用明显，近岸处流态紊乱，船型浮堤外侧流速增强；当船型浮堤向下挑时，船型浮堤下游环流作用增强，在缓流区近岸处形成局部加速区，回流范围与强度较小，水流流态平稳。

4）当船型浮堤在深水侧且下挑布置时，对水力阻碍作用较小，底部加速区范围增大，回流区受到压缩，环流作用较船型浮堤布置于浅水区时增强。

从保护岸滩的缓流促淤效果与构建生态适宜区的角度出发，船型浮堤具有较大的优势，特别是当船型浮堤长度比例小于等于0.5，淹没比例小于等于0.4，向下游挑且布置在深水区一侧时。在环流作用下，船型浮堤下游的缓流区在近岸处形成局部增速区，降低岸滩稳定性，在未来的研究中可进一步分析船型浮堤以不同间距布置时对缓流区内局部增速区的影响。

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基金资助

国家重点研究计划项目(2022YFC3202405)

开封市科技发展计划项目(2503010)