FLOW-3D®的水利应用的实践 River Hydraulics Safety and Operations Aquaculture

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1 FLOW-3D®的水利应用的实践 River Hydraulics Safety and Operations Aquaculture
Sediment Scour Moving Gates Fish Ladders 1

2 FLOW-3D ®於水利應用的主要优势 准确 友善的操作接口 离散完整的 Navier-Stokes 方程式 VOF – 模拟自由液面的变化
FDM with FAVOR 可以在正交网格上模拟复杂的几何问题

3 Finite-Difference (Control Volume) Method
scalar quantities, such as temperature and pressure are computed at cell centers vector and tensor quantities are computed at cell faces 如何用矩形网格描述复杂的形体?

4 FAVOR ® 利用 FAVOR 技术，使曲面造型的 Model 也能够顺利的以矩形网格加以描述，使分析模型不会失真。 STL 图档
FLOW-3D 网格图档

5 FAVOR 对网格数量的影响 FLOW-3D 采用 FAVOR 技术，因此同样的几何造型（如下图），FAVOR 仅需三个网格就可以描述得很精确，但是传统的 FDM 技术必须以较多的网格数量才能够达到相同的要求。 FAVOR 傳統的 FDM

6 单一mesh block不足以求解一些特殊的几何问题
为什么需要 Multi-blocks? Structured grids have some disadvantages when single mesh blocks are used. For example, when a meandering flow domain is modeled, the fine resolution used in the channel extends beyond the channel, wasting memory. Also, when modeling the flow over an object, the grid may need to be well resolved near the object to capture viscous and thermal boundary layers. This causes the near-object resolution to extend out into regions where this resolution is not needed or wanted. The solution to this dilemma is multi-block gridding. 单一mesh block不足以求解一些特殊的几何问题

7 Structured grids / multi-block grids
相鄰cell邊寬差異應控制在2倍以下! ! Linked blocks used to mesh only region of interest. Nested block enhances resolution around sphere

8 VOF（Volume of Fluid） 1975 年，Dr. Hirt & Dr. Nichols 发表 VOF 技术
1. 定义流体的液面动作状态 2. 追踪流体液面流动时的变化 3. 定义流体流动时的边界条件设定 目前所有的 CFD软件，几乎都是利用VOF来追踪自由液面的位置

9 Volume-of-Fluid (VOF) Method
Three components of VOF: F = Fluid fraction Special advection handing to accurately track sharp interface Boundary conditions at free surface (a normal pressure and no shear stress) The Volume-of-Fluid (VOF) Method was developed by FLOW-3D®’s founder, Dr. Tony Hirt, while at the Los Alamos National Lab. The VOF method provides the most accurate way to advect fluid interfaces through a computational grid while keeping the interface sharp and well defined. There are three key elements which must be in place in any CFD tool in order to be called a VOF method. First, there must be a fluid fraction variable F, which tracks the amount of fluid within a given computational cell. Second, an advection algorithm is required to not only advect F, but to keep the interface sharp. Third, free surface boundary conditions must be applied to the interface. The free surface boundary conditions are: a normal pressure and no shear stress.

10 TruVOF? 的数值验证 Flow Over Step E1 L H h1 a h2 E2 Quantity Exp. Cal.
Pool depth, h1/H Outflow depth, h2/H Pool length, L/H Nappe angle, a ? 52 Energy loss, (E1-E2)/E E1 L H A simple but computationally challenging test of a CFD code’s VOF capability is simulation of flow over a step. The flow is clearly a free surface flow because there are two fluids—one is heavy (water), and one is light (air). Also, experimental data is readily available, making it an excellent benchmark. Using the TruVOF? method in FLOW-3D? produces simulation results that are within a few percent across a range of measurements. This demonstrates the accuracy and power of FLOW-3D?. h1 a h2 E2 Data: N. Rajaratnam and M.R. Chamani, J. Hydraulic Res. 33, p.373, (1995)

11 Comparison of TruVOF® with Two-Fluid VOF
A direct comparison of TruVOF® with a two-fluid VOF scheme shows the superiority of TruVOF®. The TruVOF® method maintains a sharp interface between the air and the water, generates physically realistic results, and matches experiment. The two-fluid VOF method creates unphysical results which result from numerical diffusion between air and water. Gas regions with uniform constant pressure Gas flow Fluid/gas mixture flow Two-fluid VOF models are best applied to dispersed two-phase flow. Simulations with well separated phases should use one fluid TruVOF®

12 输入成形条件 Global Physics Pros
标准的分析流程 输入图档 建立网格 输入成形条件 Global Physics Pros 建立边界条件 给定初始条件 Preprocess Simulation Results

13 模式设定接口（Model Setup） Units Version options

14 地形几何图形与网格建立

15 如何输入高程图档 Topographic data
档案格式 x-coordinate y-coordinate z-coordinate 直接编辑prepin档 &obs avrck=-3.1, nobs=1, iob(1)=1, igen(1)=5, ftopo(1)='topo2.dat', /

16 边界条件

17 Boundaries – 使用者接口 Step 1: 选择边界的形式 Step 2: 给定所需的边界值
Boundaries – Configuration Panel: The Boundary Configuration Panel is for selection of the boundary type to apply at the boundary selected, and for setting the properties associated with that boundary type. Step 1: 选择边界的形式 Step 2: 给定所需的边界值

18 Velocity 速度边界数值可以固定或是时变 速度在边界上为均匀分布 时变速度，假设为线性变化
Boundaries – Velocity: This boundary type sets a velocity condition in the applied directions. For example, setting a u, v and w value at the X min boundary creates a flow through the boundary in those directions. The velocity can be constant or time dependant. Constant velocity boundaries are set in the dialog boxes labeled u velocity, v velocity, and w velocity. By selecting the Velocities tab a time dependant condition can be set. Time dependant boundaries are a linear interpolation between values set.

19 Pressure 边界压力可以是固定或是随时间改变 基本上边界上的压力为均匀分布 Boundaries – Pressure:
This boundary type sets a pressure condition. The pressure can be constant by setting a value in the dialog box, or time dependant by selecting the pressure button. A time dependant pressure is a linear interpolation between values set at each time. By selecting stagnation pressure the velocities upstream of the boundary are assumed to be zero. Also, a hydrostatic boundary can be set by setting ipdis = 1 in the Xput namelist.

20 Continuative Boundary Condition
代表空间上已经达到一稳定状态 流体变量如速度、温度或压力在通过边界时为定值，没有加速度 数值上为边界上物理量的梯度为零 Boundaries – Continuative: Gradients of all flow parameters in the direction normal to the boundary are set to zero resulting in the continuative boundary condition. The zero-derivative condition is intended to represent a smooth continuation of the flow through the boundary. If flow tries to enter the computational region across this type of boundary, it does so by starting from a zero velocity (stagnation) condition. In addition, the fluid surface height in free surface flows can be set at any of the four mesh boundaries at the left (low x), right (high x), front (low y) and back (high y). The surface height is only applied if the fluid is entering the domain through an outflow boundary. Assumes u, T, μ, and pressure do not change in flow direction.

21 Fluid Height 可与velocity, pressure 以及volume flow rate 一起使用
流体高度可设定为固定高度或者是随着时间变化的高度 流体高度定义于 Z 轴 不管在任何流体高度，流体都可以外流 只有流体等于或低于给定高度，流体才可以入流 Whenever pressure or velocity BC is applied along a particular mesh boundary, by default fluid can enter or leave the domain along that entire boundary. For free surface flow simulations like river flow, flow over dam, etc along with specifying pressure or velocity it is also necessary to fix fluid height (reservoir level) along that boundary. Fluid height feature which is available along with pressure and velocity BC allows the user to fix the fluid height. This feature is applicable only along X and Y min-max boundaries, the fluid height is thus always along Z direction. The value of fluid height is the Z coordinate of the fluid level. When fluid height is specified for a pressure BC the solver assumes hydrostatic pressure distribution (simulates the presence of large reservoir) along the boundary cells. Pressure BC at inlet and outlet with specified fluid height Default value = -1.0e10 = “unassigned”

22 VFR Boundary Condition
体积流率（必为正值） 可指定流体进入方向 Volume of flow rate 除了可指定流体方向外，还可以指定进入流体的高度（高度必须设定在 Z 轴方向）

23 Volume Flow Rate Boundary Condition Interpretation and Definition
Volumetric flow rate – L3/T N – direction vector N = (1, 0, 0) N = (-1, 0, 0) N = (N1, N2, 0) N = (N1, N2, 0) Flow entering at min X boundary Flow entering at max X boundary Angled flow entering at min X boundary Angled flow leaving at max X boundary

24 Wave Boundary 可给定线性波 可以同时给定速度边界条件 波浪模式是根据线性波理论 只能在 X ＆ Y 给定波浪边界 需给定波高
需给定波长或波的周期 需给定相位差（以度数为单位） 需给定平均流体高度

25

26 Outflow Boundary 流体可以从出流边界回流

27 水利工程常用的物理模型

28 Model Setup - Physics Total 22 models

29 Air Entrainment Model 29

30 Air Entrainment Model Air Entrainment 主要的生成原因是由于流体在流动的过程中并入一些微小的空气
那些工程的问题需要考虑到卷气问题? 水处理净化过程需要空气来维持水中微生物的活动 河川需要基本的含气量来维持鱼类的生存 发电设备中下游的溢洪道，卷气量可以降低穴蚀对溢洪道基座损害的机率 水跃往往伴随着卷气的生成 金属铸造的浇口与流道系统 消费性产品的流动分析 30

31 Flows with Density Variations
31

32 Flows with Density Variations
一般而言有下列几种状况需要启动变密度模式 油在水中的渗漏状况 温度差造成的湖水密度分层 卷气造成的密度变化 “Variable Density model” 允许使用者在具自由液面的单一流体下模拟此类问题 变密度模式除了求解原本单一流体方程式以外，多考虑一密度传输方程 Second order scheme 可以降低两种不同密度间流体的数值扩散 32

33 Variable Density Model Example: Buoyant flows, Thermal Stratification
温度差异导致水体的分层效应。其中靠近底层的水体温度较低、密度较大，表层的水体温度较高、密度较小。 Activate the variable density model. Define multiple fluid regions in the initial tab. Each fluid region has a different density Define density at inlet BC

34 Cavitation Model

35 Cavitation Model 穴蚀现象的生成，主要是因为流体流动造成流场中局部的压力低于流体的蒸汽压，此时可能会有气泡产生、破裂。
穴蚀将会导致水工结构物的损坏，预测穴蚀可能发生的区域是水利工程中很重要的问题之一。 穴蚀可能发生在许多水工结构物，如： 溢洪道 Spillways 净水池 Stilling basins 阀门 Valves 导管 Pipes

36 General Moving Objects
36

37 General Moving Objects
允许对象在整个计算域中移动与旋转 可以在各个方向移动与旋转 可以给定固体移动方向，或是完整的流固耦合运动 移动轨迹由使用者自行定义 流固耦合固体的运动由流场决定 在物力模式列中，点选 Moving and deforming objects 可以在这里控制物体运动、碰撞和变形的性质 可以在 Meshing & Geometry编辑物理的形状和物理性质 37

38 Modeling Control Gates
利用GMO模式仿真弧型闸门开启时的流况 固定轴承旋转 时变性角速度 利用GMO模式仿真弧型闸门开启时的流况 时变性速度运动

39 Sediment Scour Model 39

40 Sedimentation & Scour Model
模拟沈积物的侵蚀、移动和沈淀 飘移的沈积物会在静止的流域沈淀，变成河川底床的一部份 沈淀后的沈积物可能被侵蚀，然后随着河水移动 Advection of sediment due to fluid motion Settling of sediment due to gravity Entrainment of sediment into fluid 40

41 Sediment Scour Model in FLOW-3D?
侵蚀模式的假设 流体固体接口变化需藉由经验公式 侵蚀的速率可由实验调整 悬浮模式的假设 飘移，沈淀与与沈积物的再悬浮 The sediment scour model implemented into FLOW-3D?, as with all sediment scour models, is an empirical model, which means that we do not calculate the dynamics about each and every sediment particle with a first-principles approach, but rather make use of an equation that is extracted from experimental observations of scour. Once eroded, the sediment becomes suspended, and is subject to the hydrodynamic forces and gravity and may re-settle. 41

42 Particles Model 42

43 Shallow Water Model 43

44 What is a Shallow Water Flow?
浅水波方程式是使用当河流水平流动远大于垂直流动时的一种简化模式 浅水波模式可能应用的范围有：海洋、河口流、季节性的洪水、液体的涂布甚者如汽车挡风玻璃上的雨水 所有流体垂直方向的物理量都会用垂直的平均值近似，忽略垂直方向加速度。 FLOW-3D?的FAVOR和VOF数值方法非常有利于浅水波方程的求解 In order to apply the shallow water model effectively, the assumptions of the model need to be well understood. A shallow flow problem is one in which vertical variations in the geometry and the flow are small in comparison to the horizontal extent. Therefore, 3D structures such as spillways cannot be represented effectively using the Shallow Water model. Typical applications are ocean flows (typically near beaches where the vertical flow is minimal), and estuaries. Open ocean flows are not usually simulated as a shallow flow since there are usually large vertical eddies which cannot be captured. Other applications of the shallow water model include small scale problems such as liquid coatings and water flow on a windshield. These types of problems may be good candidates for the shallow water model because they tend to be very thin and exhibit small variations in the direction perpendicular to the surface. The primary limitation or requirement of the shallow water model is that there not be any large local variations in the geometry. Any large accelerations in the flow vertically would be lost numerically. The VOF and FAVOR fractional methods in FLOW-3D? lend themselves particularly well to the shallow water model. 44

45 Application of Shallow Water Model
大尺度流场分析时，完整的三维模拟有时候不是非常容易 需要很久的计算时间 (weeks) 需要非常大的计算机内存空间 浅水波模式 基本上是2 ? D的模式 垂直方向的物理量利用平均的单一值近似 可以有效的减少内存的需求 不过在水深垂直变化激烈的流场不适合使用这个模式 The application of powerful 3D CFD tools such as FLOW-3D? to large hydraulic simulations such as river flows can be challenging due to the scale of such problems. Because of the relatively low flow velocities it can take many hours of actual simulation time to achieve a steady state. The runtime can be on the order of weeks even on the fastest hardware. The usual limits of computer memory apply and so the largest model which can be simulated is limited by the amount of RAM on the computer. One possible modeling approach which can be used to solve hydraulics problems in a reasonable amount of time is the Shallow Water model. The shallow water model is essentially a 2 ? dimensional model of a 3 dimensional problem. All flow quantities including pressure and velocity are averaged in the vertical direction and that average quantity is advected in the horizontal direction. By using a shallow water model, the memory requirements of some hydraulics problems can be reduced by a significant amount. However, there are some strict limitations of the model which must be adhered to in order to achieve reasonable results. 45

46 河川侧向入流 Next: other improvements and changes

47 结构物的受力状况 在水利工程中计算水工结构物（如溢洪道、消能器、桥墩）的受力状况是非常重要的工作 流体于结构物上的作用力可分为两种:
Pressure force Viscous force 一般水利设施中，压力占流体作用力绝大部分的比例

48 Force Windows Force window 可以用来计算指定范围内固体结构物的受力状况
force window是一个3D的矩形方块，可以求得方块内不同方向的受力 A B C Figure 1: Force window encompassing multiple solid structures: 输出文件会包结构物 A,B,C三个方向的受力和力矩总和 可以计算 force window 内结构物表面受力和力矩总和 Figure 2: Force window partially encompassing a solid structure: 计算力与力矩的大小只局限于结构物在 force window 内部的区域. 力矩的计算是以原点当参考点

49 Component Pressure Force
可以在 geometry 中component 勾选压力输出选项，计算流体对对象的施力大小 “component pressure force output”只考虑所受压力，忽略黏滞力的影响 当勾选 “Pressure force output” 选项，同时也会输出压力对于原点造成的力矩

50 Example: 晃动水槽壁面受力 Next: other improvements and changes

51 Two methods: pressure output & force window
Next: other improvements and changes

52 受力大小结果输出 计算固体受力，直接勾选pressure output即可
Next: other improvements and changes

53 水利工程应用 Free surface elevation Froude number Fluid depth
Distance travelled by fluid Next: other improvements and changes

54 Thanks for your patience!!!
Next: other improvements and changes