flow3d软件-p物理模型

空化现象？FLOW-3D

v10.1

Hydraulics

Training气蚀是微小气泡核的形成，快速扩张和

。有两种类型的气泡的形成：惯性驱动（由压力引起的空化现象）：携带气体是主要形成的气泡来源热驱动（也称为热沸点）：气化的液体是主要形成的气泡来源在水工建筑物中比较常见是由惯性驱动的引起空化现象。因为气泡造成的冲击波，可以损坏固体和机械结构物。空化模型（Cavitation

）“Activate

Cavitation

Model”直接模拟气蚀

模拟气蚀产生的状况当压力小于气蚀压力时“cavitation

pressure”会有气泡生成“Characteristic

timeforformation

of

cavitationbubbles”控制气泡生成的速率气蚀气泡的生成主要取决于气蚀压力“Cavitation

pressure”网格必须足以解析气泡生成可能无法模拟气蚀刚发生的阶断，因为这时候的气泡通常远小于网格尺寸CavitationPotentialModel气蚀“Activate

CavitationPotential

Model”对固体表面气蚀影响的积分一种较有效率的计算方式：仿真 气蚀可能发生的区域并没有真正计算气泡的生成.基本计算方式是将局部流体压力与气蚀压力之间的差值对时间积分.每个格网积分所得的值 为--

“Cavitation

potential”.“Cavitation

potential”的数值越大代表气蚀发生的可能性越大.t0S

pPiCjkA)0V(

t变密度流流体内密度会发生变化无明显分界面:混溶例子:在水中的盐梯度水中热梯度可溶性污染物可压缩气体多相流变密度和多相流?流体内存在独立两相:混溶相间有明显分界面例子:水和空气（气泡）空气和微粒（灰尘）水和颗粒物（泥沙）水和油（互不溶液滴）变密度流在每个时间步内单元会被赋予一个密度密度可以是一个函数:温度纯量量的污染物浓度分散的不混溶相的浓度（空气，沉积物）多相流模型（

Drift-Flux

）多项流:流体/流体,流体/气泡,或流体/颗粒在

续气体或液体内某一相是分散时使用在水中的气泡或沙粒由于阻力和密度存在，相与相间会有速度差异：较大的相对速度:必须分别求解不同成分的速度场e.g.水滴穿过空气降落,石头 水中.–

较小的相对速度:可以视为对象相对于主要的流体飘移运动e.g.空气被卷入水中,泥沙在水中.主要适用于流场中发生较小相对速度的飘移运动Dispersed

phaseContinuous

phase多相流验证油和水验证Oil

/

WatermixtureOilWaterWaterOil/water

separator

simulation在紊流液面处掺气若你需要在

液面处考虑空气影响，那么打开

掺气和

湍流

物理模型提供三种方式建立模型:作为纯量模型(不影响流体密度)气体是零体积(仅当<2%下使用)不需要打开Scalar

物理模型Density

Evaluation

(1st

or2nd-order)(考虑体积影响）增加的纯量，使之与流体成为混合密度Density

Eval

&

Drift-flux:(考虑浮力效应影响）在单元内增加气泡阻力和相对速度允许气体在

液面处离开(脱气)固体为刚体:给定运动或耦合运动给定运动（Prescribed

motion）:

需用户指定,

会影响流体运动.耦合运动（Coupled

motion）:程序自动计算,流体和物体完全耦合运动.固定网格法网格类型:

固定不动的物体:

可以在网格内移动FAVORTM

技术:

通过面积和体积比例~时间

控制优点高效的.No

moving

mesh,

deforming

mesh

or

re-meshing.允许多个物体同时运动.No

restriction

on

distance

between

objects.No

restriction

on

complexity

of

object

motion.准确而稳定GMO

流固耦合模型移动物体:定义几何组件（可以stl

等格式）组件总数量<500每个运动物体都可以设定独立运动类型运动类型:给定运动或耦合运动6个 度

(DOF);沿固定轴旋转;沿固定点平移模型功能GMO

案例粒子模型（Particle）FLOW-3D®

可以将颗粒流中的颗粒视为Lagrangian颗粒分散的颗粒,分别追踪运动的轨迹是根据个别颗粒的力平衡计算Marker

particles主要随流体运动–不考虑飘移Mass

particles会根据密度飘移、沉积或悬浮，并可以分类成:均匀的粒径与密度均匀的粒径但不同的密度均匀的密度但不同的粒径带电粒子虽然有定义粒径大小,但并没有真正占据实际的体积颗粒-流体作用:单向的作用完整的流体颗粒耦合不考虑颗粒与颗粒之间的相互作用泥沙冲刷模型（Sediment

scour）FLOW-3D中考虑五种沉积物传输机制:飘移(沉淀)沉积物会因为重力作用沉降移动沉积物会随的水流运动带起沉积物被卷入水流中然后随着移动或沉降底床载传输沉积物沿底床表面滚动或跳动堆积沉积物会有堆积 的现象实验验证FLOW-3D

v10.1

Hydraulics

TrainingA

bench-scale

lab

model

was

built

to

simulate

the

drop

and

scour.Tovalidate

thesoftware, the

height

of

the

standingwaveagainst

the

upstream

side

of

the pier

was

compared

to

FLOW-3D

results. Matching

was

found

to

be

successful.实验验证FLOW-3D

v10.1

Hydraulics

TrainingQualitative

comparison

of

results

matched

well,

includingthe

undercut

of

the pier

(10

sec

and

80

sec

shown).Thanks

to

Allen

Lin

for

the

model

and

results!浅水模型Shallow

Water适用：水深平均流体(Depth-Averaged

Flow)假设垂直方向加速度可以忽略，且垂直方向所有变量可用其平均值代替利用二维动量方程求解利用特殊的粘度和湍流模型流动可以是层流或湍流与Viscosity

&

Turbulence

模型不兼容Laminar

model:

uses

ROUGH

(by

component)T DRAG

COEFFICIENT

(global)浅水模型网格与几何设定考虑x&y

方向二维网格重力必须在设定在z

方向Z方向必须要有2

个网格上方的网格是用来计算风切(wind

shear)流体的流动范围必须控制在下方网格利用固定点功能来给定z方向网格分布基本功能绘制几何:可以利用.stl图文件或可将.topo

高程转成stl

资料任一水平网格只能对应一个垂直高程数据范例Simulation

courtesy

of

Dan

Gessler

and

Alden

Labs增加风剪效应（Wind

Effects）Wind

shear

can

be

modeled

on

the

free

surfaceset

pressure-type

boundary

atz-max,withF=0set

tangentialvelocity

components,

constantortime-dependentset

wind

shear

coefficient

CD,WIND

(WNDSHR)set

air

density

ρair

(RHOAIR)Can

be

used

in

3-D

models

too!2S

CD,WINDairuWIND增加科里奥利效应（Coriolis

effect）For

very

large s,

effects

of

the

Earth’s

rotation

are

importantactivate

Non-Inertial

Reference

Frame

>

Geophysical

Fluid

Flow

physicsspecify

the

mean

latitude

of

the (assumes

it’s

onEarth)Can

be

used

in

3-D

flows,

too!3-D

和2-D

混合网格建模可以是三维网格和二维浅水网格混合使用二维速度在交界面处

值到三维网格块–

当流动从二维到三维网格时假设没有速度分布三维网格块解析细部的流体，而二维网格块也计算流动在二维浅水网格块内可以使用三维网格（linked

to

or

nested），但是反之不行紊流？紊流是指流体从一种稳定状态向另一种稳定状态变化过程中的一种无序状态，具体是指流体流动时各质点间的惯性力占主要地位，流体各质点不规则地流Reynolds

Averaged

Navier-Stokes

(RANS)

models.Large

Eddy

Simulation

(LES)models.FLOW-3D

v10.1

Hydraulics

Training紊流流动及混合所需的参数(momentum,

temperature,

density,

contaminants,etc.)要比层流更有效影响到施压流体上的剪应力与拖曳力•模拟紊流模型–典型的方法什么时候应该打开紊流模型?FLOW-3D

v10.1

Hydraulics

Training把无量 偌数与临界值对比

(湍流的开始)不止一个雷偌数，不止一个湍流转变数值！常见的例子:h»

Internal

pipe

&duct

flow

(D =

hydraulic

diameter)»

Externalflat-plate

flow

(x=

distance

alongplate)»

External

flowaround

an

object

(Dob

=

object

width)湍流开始处雷偌数的数值是近似的Re

f

uavg

Dh,eff

2,300Dh

fRe

f

u

freestream

x

500,000x

fRe

f

u

freestream

Dob

20,000Dob

f滑移条件“friction

coefficient

”摩擦系数是定义流体在物件和壁面边界处是否滑移“Roughness”粗糙度设置是不同的，并在之后进行FREE-SLIP

(FRCOF

or

OFRCOF

=

0PARTIAL-SLIP

(FRCOF

orOFRCOF

>

0)NO-SLIP

(DEFAULT:

FRCOF

or

OFRCOF

=-1)FLOW-3D

v10.1

Hydraulics

Training湍流模型（优缺点）MODEL

OPTIONPROSCONSPrandtl

Mixing

LengthLowest

computational

cost.

Solves

for

turbulentviscosityas

a

function

of

shear.

A

slight

improvementon

one

ofthe

earliest

numericmodels.Requires

fully

developed,

nearly

steady,uniform

flow.

Advection,

diffusion,

and

thetime-rate

of

change

of

turbulent

energy

areneglected.One-equation(turbulent

energymodel)A

simplification

of

the

standard

two-equation

model.

Lowcost,

decent

for

relatively

uniform

flows.

Includesconvection

and

diffusion,

production

of

TKE

duetoshearing

and

buoyancy

effects,

diffusion,

and

dissipation.Better

accuracy

and

mu ore

robustthanthePrandtlmodel.Requires

the

user

to

specify

a

turbulentmixing

length

to

give

accurate

results

forturbulent

diffusion

(decay),

and

is

verysensitive

to

the

selected

mixing

lengthvalue.

Not

ideal

for

flows

aroundcomplexgeometry.Two-equation(κ-ε

standardmodel)Widely

used

forreal-world

problems,

and

givesreasonable

results

for

heat

transfer.

Coefficients

derivedempirically.

This

model

solves

transport

equations

forturbulentkinetic

energy

and

turbulent

dissipation

rate.Valid

only

for

fully

turbulent(smooth

torough)

flows,

not

great

for

high

strain

rates,swirling

flows,

or

curved

streamlines.

Doesnot

model

wall

heat

or

mass

transfer

well.Renormalized

Group(κ-ε

RNG

model)An

improved

k-e

model,

with

some

coefficientscalculateddynamically

and

the

rest

determined

through

statisticalysis.

Better

for

transitional

flows

and

all

the

othercons

of

the

standardk-e

model

except

swirling.Not

ideal

for

highly

swirled

flows

(cyclonesand

shear-stress-induced

secondary

flows).Otherwise,

usually

the

best

choice.Large

Eddy

Simulation(LES)Approaches

direct

numerical

simulation

(DNS)

by

directlyresolving

eddies

larger

than

the

computation

cell

scale.Applies

the

Smagorinsky

kinematic

viscosity

model

foreddies

smaller

than

a

cell(sub-grid

model).

Containsmore

information

than

other

models

(e.g.,

magnitudeandstd.

dev.

of

turbulent

fluctuations).Requires

very

fine

mesh.

Developed

foratmospheric

research:

not

originallyintended

for

wall-bounded

flows

(FLOW-3D

uses

log-law

approximation).Development

of

LES

models

continues.There

are

relatively

few

validations

for

real-world

problems.FLOW-3D

v10.1

Hydraulics

Training什么时候应该考虑表面粗糙度（Surface

Roughness

）？FLOW-3D

v10.1

Hydraulics

Training表面粗糙度对流动可能会产生或可能不产生影响湍流流动在壁面处可能是水力光滑的、完全粗糙的、过渡“过渡”含