asme - cfd fundamentals
TRANSCRIPT
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 1/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 1
CFD Fundamentals and Applications
Metin Ozen, Ph.D., CFD Research Corpo rat ion
Ashok Das, Ph.D., Appl ied Mater ials
K im Parnel l, Ph .D ., Parnel l Engineer ing and Consu l t ing
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 2/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 2
AGENDA
n 9:00-9:05 Introductions by Scott Burr
n 9:05-10:30 CFD Fundamentals by Metin Ozen
n 10:30-10:45 Break
n 10:45-12:00 Applications in Semiconductor Industryby Ashok Das
n 12:00-1:00 LUNCH
n 1:00-2:15 Applications in Biomedical Industry by KimParnell
n 2:15-2:30 Breakn 2:30:3:45 CFD Applications by Metin Ozen
n 3:45-4:00 Q&A
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 3/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 3
Some CFD Books
n Computational Fluid Dynamics: TheBasics with ApplicationsJohn David Anderson
n Computational Methods for FluidDynamics Joel H. Ferziger
n Turbulence Modeling for CFD David C.Wilcox
n http://www.sali.freeservers.com/engineering/cfd/cfd_books.html
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 4/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 4
Definitions of CFD on the WEB
n Computational Fluid Dynamics (CFD); the simulation
or prediction of fluid flow using computers
n Computer modeling of fluid behaviour, for example
the flow of fuel/air mixture into a combustionchamber.
n Computational Fluid Dynamics refers to
computational solutions of differential equations,
such as the Navier Stokes set, describing fluid
motion.
n …
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 5/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 5
What is CFD?1
n CFD has grown from a mathematical curiosity to
become an essential tool in almost every branch of
fluid dynamics, from aerospace propulsion to
weather prediction. CFD is commonly accepted asreferring to the broad topic encompassing the
numerical solution, by computational methods, of the
governing equations which describe fluid flow, the
set of the Navier-Stokes equations, continuity and
any additional conservation equations, for exampleenergy or species concentrations.
1 - http://www.cranfield.ac.uk/sme/cfd/
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 6/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 6
Biochips
BioMedical
MEMS
Semiconductor
Equipment & Processes
Environmental
CBW Protection
Fuel Cells
Power Conversion
Plasmas
Non-Equilibrium
Thermal
Combustion
PropulsionMicroelectronics
Photonics
Aerodynamics
Aerostructures
CFD RESEARCH CORPORATIONCFD RESEARCH CORPORATION -- Major Major Application Application Areas of CFD Areas of CFD
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 7/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 7
What is CFD?
n As a developing science, Computational FluidDynamics has received extensive attentionthroughout the international community since theadvent of the digital computer. The attraction of the
subject is twofold. Firstly, the desire to be able tomodel physical fluid phenomena that cannot be easilysimulated or measured with a physical experiment,for example weather systems or hypersonicaerospace vehicles. Secondly, the desire to be able to
investigate physical fluid systems more costeffectively and more rapidly than with experimentalprocedures.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 8/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 8
What is CFD?
n There has been considerable growth in the
development and application of Computational Fluid
Dynamics to all aspects of fluid dynamics. In design
and development, CFD programs are now consideredto be standard numerical tools, widely utilised within
industry. As a consequence there is a considerable
demand for specialists in the subject, to apply and
develop CFD methods throughout engineering
companies and research organisations.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 9/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 9
Commercial CFD Codes - 1
n ACRi
n ARSoftware (TEP: a combustion analysis tool for windows)
n COSMIC NASA
n Fluent Inc. (FLUENT, FIDAP, POLYFLOW, GAMBIT, TGrid, Icepak, Airpak, MixSim)
n Flowtech Int. AB (SHIPFLOW: analysis of flow around ships)
n Fluid Dynamics International, Inc. (FIDAP)
n ANSYS-CFX (CFX: 3D fluid flow/heat transfer code)
n ICEM CFD (ICEM CFD, Icepak)
n KIVA (reactive flows)
n CFD Research Corporation (ACE: reactive flows)
n Computational Dynamics Ltd. (STAR-CD)
n Analytical Methods, Inc. (VSAERO, USAERO, OMNI3D, INCA)
n AeroSoft, Inc. (GASP and GUST)
n Ithaca Combustion Enterprises (PDF2DS)
n Flow Science, Inc. (FLOW3D)
n
ALGOR, Inc. (ALGOR)n Engineering Mechanics Research Corp. (NISA)
n Reaction Engineering International (BANFF/GLACIER)
n Combustion Dynamics Ltd. (SuperSTATE)
n AVL List Gmbh. (FIRE)
n IBM Corp. catalogue (30 positions)
n Sun Microsystems catalogue (70 positions)
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 10/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 10
Commercial CFD Codes – 2
n Cray Research catalogue (100 positions)
n Silicon Graphics, Inc. catalogue (75 positions)
n Pointwise, Inc. (Gridgen - structured grids)
n Simulog (N3S Finite Element code, MUSCL)
n Directory of CFD codes on IBM supercomputer environment
n ANSYS, Inc. (FLOTRAN)
n Flomercis Inc. (FLOTHERM)
n Computational Mechanics Corporation
n Computational Mechanics Company, Inc. (COMCO)
n KASIMIR (shock tube simulation program)
n Livermore Software Technology Corporation (LS-DYNA3D)
n Advanced Combustion Eng. Research Center (PCGC, FBED)
n NUMECA International s.a. (FINE, FINE/Turbo, FINE/Aero, IGG, IGG/Autogrid)
n Computational Engineering International., Inc. (EnSight, ...)
n Blocon Software Agency (HEAT2, HEAT3)
n Adaptive Research Corp. (CFD2000)
n Unicom Technology Systems (VORSTAB-PC)
n Incinerator Consultants Incorporated (ICI)
n PHOENICS/CHAM (multi-phase flow, N-S, combustion)
n Innovative Aerodynamic Technologies (LAMDA)
n XYZ Scientific Applications, Inc. (TrueGrid)
n South Bay Simulations, Inc. (SPLASH)
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 11/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 11
Commercial CFD Codes - 3
n PHASES Engineering Solutions
n Engineering Sciences, Inc. (UNIC)
n Catalpa Research, Inc. (TIGER)
n Swansea NS codes (LAM2D, TURB)
n Engineering Systems International S.A. (PAM-FLOW, PAM-FLUID)
n Daat Research Corp. (COOLIT)
n Flomerics Inc. (FLOVENT)
n Innovative Research, Inc.
n Centric Engineering Systems, Inc. (SPECTRUM)
n Blue Ridge Numerics, Inc.
n WinPipeD
n Exa Corporation (PowerFLOW)
n Polyflow s.a.
n Flow Pro
n Computational Aerodynamics Systems Co.
n Tahoe Design Software
n ADINA-F
n YFLOW
n PSW
n Advanced Visual Systems
n Flo++
n KSNIS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 12/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 12
Commercial CFD Codes - 4
n Flowcode
n Concert
n SMARTFIRE
n VISCOUS
n Polydynamics
n Cullimore and Ring Technologies, Inc. (SINDA/FLUINT, SINAPS)
n Linflow (ANKER - ZEMER ENGINEERING)
n PFDReaction
n Airfoil Analysis
n Institute of Computational Continuum Mechanics GmbH
n CFD++
n RADIOSS-CFD
n VECTIS
n MAYA Simulation
n Compass
n Arena Flow
n Newmerical Technologies International
n CFDpc
n NIKA EFDLab
n SC/Tetra
n TES International
n ACUITIV
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 13/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 13
Computational Fluid Dynamics2
n Computational Fluid Dynamics is concerned with
obtaining numerical solution to fluid flow problems
by using computers. The advent of high-speed and
large-memory computers has enabled CFD to obtainsolutions to many flow problems including those that
are compressible or incompressible, laminar or
turbulent, chemically reacting or non-reacting.
2 - http://www.sali.freeservers.com/engineering/cfd/#gotop
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 14/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 14
Computational Fluid Dynamics
n The equations governing the fluid flow problem are
the continuity (conservation of mass), the Navier-
Stokes (conservation of momentum), and the energy
equations. These equations form a system of couplednon-linear partial differential equations (PDEs).
Because of the non-linear terms in these PDEs,
analytical methods can yield very few solutions.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 15/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 15
Governing (Navier-Stokes) Equations(in Cartesian Tensor form)
n Continuity - Conservation of mass
??/?t + ?(?ui)/?xi = 0
n Navier-Stokes - Conservation of Momentum
?(?vi)/?t + ?(?viv j)/?x j = ?Bi - ?p/?xi - ?/?xi [2/3µ(?v j /?x j)]
+ ?/?x j [µ(?vi /?x j + ?v j /?xi)]
(For compressible and viscous flows)
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 16/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 16
Computational Fluid Dynamics
n In general, closed form analytical solutions are
possible only if these PDEs can be made linear, either
because non-linear terms naturally drop out (eg., fully
developed flows in ducts and flows that are inviscid
and irrotational everywhere) or because nonlinear
terms are small compared to other terms so that they
can be neglected (eg., creeping flows, small
amplitude sloshing of liquid etc.). If the non-linearities
in the governing PDEs cannot be neglected, which isthe situation for most engineering flows, then
numerical methods are needed to obtain solutions.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 17/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 17
Governing (Navier-Stokes) Equations
n Continuity - Conservation of mass
??/?t + ?(?u)/?x + ?(?v)/?y + ?(?w)/?z = 0
(For compressible and viscous flows)
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 18/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 18
Governing (Navier-Stokes) Equations
n Conservation of Momentum
?[?u/?t + u?u/?x + v?u/?y + w?u/?z] = ?Bx - ?p/?x -(2/3)?/?x[µ(?u/?x+?v/?y + ?w/?z)] + 2?/?x(µ?u/?x) + ?/?y[µ(?u/?y +?v/?x)]+?/?z[µ(?u/?z+?w/?x)]
?[?v/?t + u?v/?x + v?v/?y + w?v/?z] = ?By - ?p/?y -(2/3)?/?y[µ(?u/?x+?v/?y + ?w/?z)] + 2?/?y(µ?v/?y) + ?/?z[µ(?v/?z +?w/?y)]+?/?x[µ(?v/?x+?u/?y)]
?[?w/?t + u?w/?x + v?w/?y + w?w/?z] = ?Bz - ?p/?z -(2/3)?/?z[µ(?u/?x+?v/?y + ?w/?z)] + 2?/?z(µ?w/?z) + ?/?x[µ(?w/?x +?u/?z)] + ?/?y[µ(?w/?y + ?v/?z)]
(For compressible and viscous flows)
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 19/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 19
Computational Fluid Dynamics
n CFD is the art of replacing the differential equation
governing the Fluid Flow, with a set of algebraic
equations (the process is called discretization), which
in turn can be solved with the aid of a digital
computer to get an approx imate solution. The well
known discretization methods used in CFD are Finite
Difference Method (FDM), Finite Volume Method
(FVM), Finite Element Method (FEM), and Boundary
Element Method (BEM).
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 20/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 20
CFD – SOLUTION METHODS
n FDM – Resistance Network
n FEM – [K] {u} = {F}
n FVM – [A] {Φ} = {Q}
n BEM – [B] {d} = {P}
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 21/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 21
Computational Fluid Dynamics2
n Computational Fluid Dynamics (CFD) provides a good
example of the many areas that a scientific
computing project can touch on, and its relationship
to Computer Science. Fluid flows are modeled by a
set of partial differential equations, the Navier-Stokes
equations. Except for special cases no closed-form
solutions exist to the Navier-Stokes equations.
2 - http://www.sali.freeservers.com/engineering/cfd/#gotop
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 22/63
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 23/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 23
CFD – PROBLEM SIZE
n On the discretized mesh the Navier-Stokes equations take the
form of a large system of nonlinear equations; going from the
continuum to the discrete set of equations is a problem thatcombines both physics and numerical analysis; for example, it
is important to maintain conservation of mass in the discreteequations. At each node in the mesh, between 3 and 20 variablesare associated: the pressure, the three velocity components,
density, temperature, etc. Furthermore, capturing physically
important phenomena such as turbulence requires extremelyfine meshes in parts of the physical domain. Currently meshes
with 20 000 to 2 000 000 nodes are common, leading to systemswith up to 40 000 000 unknowns.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 24/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 24
CFD - SOLVERS
n That system of nonlinear equations is typically solved by aNewton-like method, which in turn requires solving a large,sparse system of equations on each step.
n Methods for solving large sparse systems of equations are a hottopic right now, since that is often the most time-consuming partof the program, and because the ability to solve them is thelimiting factor in the size of problem and complexity of thephysics that can be handled
n Direct methods, which factor the matrices, require morecomputer storage than is permissible for all but the smallestproblems.
n Iterative methods use less storage but suffer from a lack ofrobustness: they often fail to converge.
n The solution is to use preconditioning; that is, to premultiply thelinear system by some matrix that makes it easier for theiterative method to converge.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 25/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 25
CFD – PARALLEL PROCESSING
n CFD problems are at the limits of computational
power, so parallel programming methods are used.
That brings in the research problem of how to
partition the data to assign parts of it to different
processors; usually domain decomposition methods
are applied. Domain decomposition is often
expressed as a graph partitioning problem, namely
finding a minimum edge cut partitioning of the
discrete mesh, with roughly the same number ofnodes in each partition set.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 26/63
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 27/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 27
TYPICAL PROCEDUREn CONCEPT/DESIGN
n GEOMETRY
n DISCRETIZATION/MESHING
n ENVIRONMENT – VOLUME CONDITIONS
– BOUNDARY CONDITIONS
– INITIAL CONDITIONS
n SOLUTION
n VISUALIZATION
n (OPTIMIZATION)
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 28/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 28
CFD – PROBLEM SIZE3
n In CFD, the flow region or calculation domain is divided into a
large number of finite volumes or cells. The governing partial
differential equations are discretized using a wide range oftechniques: finite difference, finite volume or finite element. This
provides a set of algebraic equations (corresponding to therespective partial differential equations) for each dependentvariable in each cell volume or cell. A two dimensional
isothermal incompressible flow is governed by three equations,
namely, the continuity equation (conservation of mass), and twomomentum equations (Newton's Second Law), one for each
coordinate. For example consider the flow between the twoparallel plates shown in the figure.
3 - http://www.cfdnet.com
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 29/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 29
CFD – PROBLEM SIZE3
n For example consider the flow between the two parallel plates
shown in the figure.
n If the calculation domain is divided into 100 rectangular cells,
then there will be 100 algebraic equations for each velocitycomponent and 100 equations for the pressure, giving a total of
300 simultaneous algebraic equations.
3 - http://www.cfdnet.com
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 30/63
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 31/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 31
CFD – FLUID PROPERTIES
n Fluid is defined as a substance that cannot resist
stress by static deformation.
n Both gases and liquids are fluids.
n Density : defined as the mass of a small fluid element
divided by its volume (units in kg/m3)
volume
mass=ρ
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 32/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 32
CFD – FLUID PROPERTIES
n Viscosity: is defined in terms of the force needed to
pull a flat plate at constant speed across a layer of
fluid (Units in N.s/m2 or Poise)
n Kinematic viscosity is defined as
Layer of fluid
vF
dy
duµτ =
Shear strain
Shear stress
ρ
µν =
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 33/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 33
CFD – NEWTONIAN/NON-NEWTONIAN
•Newtonian FluidFluids for which the shear stress-shear
rate relation is a straight line passing
through the origin.
•Common Newtonian FluidsWater and air
•Non-Newtonian FluidFluids that have a viscosity which
may be a function of not only the fluid
velocity, but also the velocity gradient
•Common Non-Newtonian FluidsBlood and alcohol
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 34/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 34
CFD – EFFECT OF VISCOSITY
n Viscosity is a kind of internal friction.
n Viscosity prevents neighboring layers of fluid
from sliding freely past one another.
n Fluid in contact with the wall is stationary (no-s l ip
condi t ion ).
Velocity of fluid varies from zero to a maximum along the axis
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 35/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 35
CFD – REYNOLDS NUMBER
n Reynolds number is a dimensionless number.
n Reynolds number is the ratio of the inertial toviscous forces. It is defined as:
n Flow is characterized as LAMINAR orTURBULENT based on the Reynolds number
(>2100 turbulent)
µρvL=Re
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 36/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 36
CFD – LAMINAR/TURBULENT
Re=1.54
Re=9.6
Re=13
Re=105
Re=150
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 37/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 37
CFD – LAW OF CONTINUITY
Mass Conservation: the rate of change of the conserved
quantity within a control volume minus the rate at which theconserved quantity leaves the control volume
A1V 1
A2V 2
2211 AV AV Adz
dt
d ><−>=<><∫ ρρρ
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 38/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 38
CFD – CONSERVATION OF MOMENTUM
Newton’s second law states that the time rate of change ofthe momentum of a fluid element is equal to the sum of the
forces on the element.
g pvvvt
ρτρρ +∇−∇−⋅∇−=∂∂ ].[][
Rate of change
of momentum
Convection Pressure Viscous Gravitational
Surface forces Body forces
Navier-Stokes Equation
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 39/63
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 40/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 40
CFD – COMPRESSIBLE FLUIDSn When density varies appreciably as a result of pressure
and temperature. The static temperature becomes afunction of velocity and stagnation temperature.
n Compressibility becomes important when the MachNumber becomes greater than about 0.3.
n Mach Number is defined as the ratio of an object’s speedto the speed of sound in the medium through which theobject is traveling:
n when M is less than 1 the flow is subsonic, whilesupersonic flows are with Mach numbers greater thanone.
a
v M =
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 41/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 41
CFD – BOUNDARY LAYER
The no-slip boundary condition at the wall leads to the formation a
Boundary Layer .
A boundary layer is a thin fluid layer near the wall which experiences
velocity variations.
Inside the boundary layer the fluid velocity goes from some finite value
at the boundary layer edge to zero at the wall in a very short distance.
dyv
u)1(*
0
∫ ∞
−=δ
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 42/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 42
CFD – BOUNDARY LAYER
x
y
u
δ
U=0.99u
Flow
Boundary layer thickness
u
U
δ*
Flow
Displacement thickness
δ is defined as the
distance from the wall
where the velocity has
increased to 99 percent
of the freestreamvelocity.
δ* is defined as the
distance to which
streamlines outside the boundary layer are
displaced away from the
wall.
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 43/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 43
CFD – SOME PLANNING
n Is the flow laminar or turbulent?
n Is the fluid Newtonian or Non-Newtonian?
n Is the fluid compressible or incompressible?
n Is boundary layer and near wall solution of importance?
n What are the fluid properties and are they dependent on statevariables (T, P,..)?
n What are the dominant physics?
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 44/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 44
CFD-ACE(U) Introduction and Overview
CFD – APPLICATIONS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 45/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 45
n CFD-ACE+ System
– CFD-ACE(U) Modules
– Unique Attributes
n Theory
– General Transport Equation
– Discrete Methods
– Solution Procedure
– Linear Equation Solvers – Under-Relaxation
n Graphical User Interface
CFD – CFD-ACE+ OVERVIEW
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 46/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 46
(1) Geometry and Grid Generation
(2) Problem Setup
(4) Post Processing
(3) Solution Generation
CFD-GEOM CFD-GUI CFD-VIEW
Input Files Graphical Results
Batch Solver
CFD-ACE(U)
Text Results
Computational Gridand BC / VC Locations
CFD – CFD-ACE+ SYSTEM
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 47/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 47
Optional Modules Optional Modules
FLOW
HEAT TRANSFER
TURBULENCE
M IXING
USER SCALAR
RADIATION
CAVITATION
GRID DEFORMATION
STRESS
PLASMA
ELECTRIC
MAGNETIC
ELECTROPLATING
ELECTROKINETICS
BIO-CHEMISTRY
FREE SURFACES
SPRAY
TWO-FLUID
MONTE-CARLO RAD
Your Building Blocks for a Multi-Disciplinary Simulation
Core Modules
CFD – CFD-ACE+ MODULES
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 48/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 48
n Structured or Unstructured Grid Systems
– quadrilateral ( ), hexahedral ( )
– triangle ( ), tetrahedral ( ), prism ( ), polyhedral ( )
+ =n Arbitrary Interfaces
– mix and match grid systems
– parametric part studies
– fully conservative
Velocity Vectors
on Second Design
Stream Traces on
First Design
Close-Up of Interface
CFD – UNIQUE ATTRIBUTES
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 49/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 49
n User Subroutines
– ability to customize the solver for special needs
• boundary conditions
• properties
• source terms
• output• initial conditions
• time step
• grid deformation
• much more...
11.6
3.4 2.6
1.8
1.0
6.4
0
4
8
12
16
0 4 8 12 16
S p e e d u p F
a c t o r
Number of Processors
Ideal Speedup
Actual Speedup
n
Parallel Processing – optional feature
– automatic domain decomposition
CFD – UNIQUE ATTRIBUTES
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 50/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 50
Control Volume
t ∂∂ρφ
φφφρρφ
S t
+∇Γ •∇=•∇+∂
∂)()( V
r
transient convection diffusion source
diffusion
convection convection
diffusion
source
CFD – TRANSPORT EQUATION
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 51/63
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 52/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 52
n Calculation Domain Sub-divided into
Discrete Control Volumes (Cells)
– grid generation process
n Variables Calculated at Centers of Cells
– assumed constant over entire cell
6 equally spaced cells 8 cells with stretching
n Build Equation for Each Variable at Each Cell
φφφφφφφφ S aaaaaaa L L H H S S N N W W E E P P ++++++=S
N L
H
W EP
CFD – DISCRETE METHODS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 53/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 53
S
PW
N
E
n Each anb Represents Effects of Convection and
Diffusion
w
w
wwwW Aua ∆
Γ +−= ρ
W www Au φρ
w
w
P W w A
∆−
Γ )( φφ
– e.g., at the west face
• convection =
• diffusion =
– rearrange and assemble link coefficients
∑= nb P aa
uw
φφφ S aa nbnb P P += ∑
CFD – DISCRETE METHODS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 54/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 54
u
x
n Spatial Differencing Scheme Determines Face Values
– 1st-order upwind, central, 2nd-order upwind, etc.
x
x
x PW
<≥
=0if
0if
w P
wW
wu
u
φ
φφ1st-upwind
2 P W
w
φφφ
+=central
<
≥=
0if
2
1-
2
3
0if 2
1-
2
3
wW P
wWW W
w
u
u
φφ
φφφ2nd-upwind
n Upwind Blending Used to Maintain Stability
order higher upwind1st) 1(
−− −+= www φφφ α α
(α is a user input)
CFD – DISCRETE METHODS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 55/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 55
n Source Term ( S ) Contains Terms Other Than Convection and
Diffusion
– transient term, boundary conditions, under-relaxation, etc.
– linearized P P U S S S φ+=
P P U nbnb P P S S aa φφφ ++=
∑ U nbnb P P P S aS a +=− ∑ φφ)(
n Final Equation
CFD – DISCRETE METHODS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 56/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 56
At t=tf Prescribe Initial Flow FieldAt t=tf Prescribe Initial Flow Field
t = t + ∆tt = t + ∆t
Evaluate Link Coefficients (a’s)Evaluate Link Coefficients (a’s)
Solve VelocitiesSolve Velocities
Evaluate Mass ImbalancesEvaluate Mass Imbalances
Solve Pressure CorrectionSolve Pressure Correction
Correct p, u, v, wCorrect p, u, v, w
Solve EnthalpySolve Enthalpy
Solve Mixture/Species FractionsSolve Mixture/Species Fractions
StopStop
Repeat For EachSolution Iteration
(until solution stops changing)
Repeat For EachSolution Iteration
(until solution stops changing)
Repeat For Each Time Step
(transient simulations only)
Repeat For Each Time Step
(transient simulations only)
Solve Turbulence / Scalar / Etc.Solve Turbulence / Scalar / Etc.
SIMPLEC
CFD – SOLUTION PROCEDURE
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 57/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 57
n Need to Solve Sparse Matrix of Equations
=
RφA
=
21
1
12
231
123
321
nn
n
nn
nnn
nnn
nnn
aa
aaa
aaa
aaa
aaa
A
n Use an Iterative Linear Equation Solver
– conjugate gradient squared (CGS) – conjugate gradient squared + preconditioning (CGS+Pre)
– algebraic multigrid (AMG)
# cells
# cells
CFD – LINEAR EQUATION SOLVERS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 58/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 58
n Anywhere in Solution Procedure where SOLVE is
Found
Solve φSolve φ
Attempt to Solve Attempt to SolveR A =φ
DONEDONE
STOP with WARNINGSTOP with WARNING
sweep = sweep + 1sweep = sweep + 1
yes
no
sweep > maxsweeps
<−∑ *φφyes
no
criteria
(criteria and maxsweeps are user inputs)
CFD – LINEAR EQUATION SOLVERS
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 59/63
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 60/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 60
n Linear Under-Relaxation (Auxiliary Variables)
– auxiliary variables are not directly solved for but arecomputed during the solution procedure
• density, pressure, temperature, viscosity, etc. – specifies the amount of “correction” to be applied
φφφ ′+= oldnew α (α is a user input)
α is bounded from 0.0 to 1.0 with 1.0 the
default
– decreasing the value of α adds constraint
(stability)
– decreasing the value of α slows convergence
CFD – UNDER RELAXATION
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 61/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 61
(1) Geometry and Grid Generation
(2) Problem Setup
(4) Post Processing
(3) Solution Generation
CFD-GEOM CFD-GUI CFD-VIEW
Input Files Graphical Results
Batch Solver
CFD-ACE(U)
Text Results
Computational Gridand BC / VC Locations
CFD – GRAPHICAL USER INTERFACE
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 62/63
ASME-SCVS Professional Development Series CFD Fundamentals & Applications 62
n What CFD-GUI Is:
– graphical front end to the CFD-ACE(U) solver
– expert system for setting up multi-disciplinary
simulations• guides user through the setup process
• protects user from inappropriate inputs
• provides reasonable default inputs
– solver controller (submit / save / stop)
– solver monitor (residuals / output)
n What CFD-GUI Is Not:
– CFD-GUI is not a solver
CFD – GRAPHICAL USER INTERFACE
8/14/2019 ASME - Cfd Fundamentals
http://slidepdf.com/reader/full/asme-cfd-fundamentals 63/63
Graphics Area
Title Bar Menu Bar
Tool Bar
Control Panel
Model Explorer
Status Line
CFD – GRAPHICAL USER INTERFACE