Computational Fluid Dynamics (CFD) U7AEA29 - PowerPoint PPT Presentation

Loading...

PPT – Computational Fluid Dynamics (CFD) U7AEA29 PowerPoint presentation | free to download - id: 66bba2-MWNiM



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Computational Fluid Dynamics (CFD) U7AEA29

Description:

Computational Fluid Dynamics (CFD) U7AEA29 Dr. S. Senthil Kumar Associate Professor Dept. of Aeronautical Engineering Vel Tech Dr. RR & Dr. SR Technical University – PowerPoint PPT presentation

Number of Views:18
Avg rating:3.0/5.0
Date added: 19 February 2020
Slides: 49
Provided by: DrS100
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Computational Fluid Dynamics (CFD) U7AEA29


1
Computational Fluid Dynamics (CFD) U7AEA29
  • Dr. S. Senthil Kumar
  • Associate Professor
  • Dept. of Aeronautical Engineering
  • Vel Tech Dr. RR Dr. SR Technical University
  • Avadi, Chennai
  • .

2
Outline
  • What is CFD?
  • Why use CFD?
  • Where is CFD used?
  • Physics
  • Modeling
  • Numerics
  • CFD process
  • Resources

3
What is CFD?
  • What is CFD and its objective?
  • Computational Fluid Dynamics
  • Historically Analytical Fluid Dynamics (AFD) and
    EFD (Experimental Fluid Dynamics) was used. CFD
    has become feasible due to the advent of high
    speed digital computers.
  • Computer simulation for prediction of fluid-flow
    phenomena.
  • The objective of CFD is to model the continuous
    fluids with Partial Differential Equations (PDEs)
    and discretize PDEs into an algebra problem
    (Taylor series), solve it, validate it and
    achieve simulation based design.

4
Why use CFD?
  • Why use CFD?
  • Analysis and Design
  • Simulation-based design instead of build test
  • More cost effectively and more rapidly than with
    experiments
  • CFD solution provides high-fidelity database for
    interrogation of flow field
  • Simulation of physical fluid phenomena that are
    difficult to be measured by experiments
  • Scale simulations (e.g., full-scale ships,
    airplanes)
  • Hazards (e.g., explosions, radiation, pollution)
  • Physics (e.g., weather prediction, planetary
    boundary layer, stellar evolution)
  • Knowledge and exploration of flow physics

5
Where is CFD used? (Aerospace)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

F18 Store Separation
Wing-Body Interaction
Hypersonic Launch Vehicle
6
(No Transcript)
7
Where is CFD used? (Appliances)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

Surface-heat-flux plots of the No-Frost
refrigerator and freezer compartments helped
BOSCH-SIEMENS engineers to optimize the location
of air inlets.
8
Where is CFD used? (Automotive)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

External Aerodynamics
Undercarriage Aerodynamics
Interior Ventilation
Engine Cooling
9
Where is CFD used? (Biomedical)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

Medtronic Blood Pump
Temperature and natural convection currents in
the eye following laser heating.
10
Where is CFD used? (Chemical Processing)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

Polymerization reactor vessel - prediction of
flow separation and residence time effects.
Twin-screw extruder modeling
Shear rate distribution in twin-screw extruder
simulation
11
Where is CFD used? (HVACR)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

Flow pathlines colored by pressure quantify head
loss in ductwork
12
Where is CFD used? (Hydraulics)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

13
Where is CFD used? (Marine)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

14
Where is CFD used? (Oil Gas)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

Volume fraction of gas
Flow vectors and pressure distribution on an
offshore oil rig
Volume fraction of oil
Volume fraction of water
Analysis of multiphase separator
Flow of lubricating mud over drill bit
15
Where is CFD used? (Power Generation)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

Flow around cooling towers
Pathlines from the inlet colored by temperature
during standard operating conditions
Flow pattern through a water turbine.
16
Where is CFD used? (Sports)
  • Where is CFD used?
  • Aerospace
  • Appliances
  • Automotive
  • Biomedical
  • Chemical Processing
  • HVACR
  • Hydraulics
  • Marine
  • Oil Gas
  • Power Generation
  • Sports

17
Physics
  • CFD codes typically designed for representation
    of specific flow phenomenon
  • Viscous vs. inviscid (no viscous forces) (Re)
  • Turbulent vs. laminar (Re)
  • Incompressible vs. compressible (Ma)
  • Single- vs. multi-phase (Ca)
  • Thermal/density effects and energy equation (Pr,
    g, Gr, Ec)
  • Free-surface flow and surface tension (Fr, We)
  • Chemical reactions, mass transfer
  • etc

18
Physics
Fluid Mechanics
Inviscid
Viscous
Laminar
Turbulence
External (airfoil, ship)
Internal (pipe,valve)
Incompressible (water)
Compressible (air, acoustic)
Components of Fluid Mechanics
19
Navier-Stokes Equation
Claude-Louis Navier
George Gabriel Stokes
20
Modeling
  • Mathematical representation of the physical
    problem
  • Some problems are exact (e.g., laminar pipe flow)
  • Exact solutions only exist for some simple cases.
    In these cases nonlinear terms can be dropped
    from the N-S equations which allow analytical
    solution.
  • Most cases require models for flow behavior
    e.g., Reynolds Averaged Navier Stokes equations
    (RANS) or Large Eddy Simulation (LES) for
    turbulent flow
  • Initial Boundary Value Problem (IBVP), include
    governing Partial Differential Equations (PDEs),
    Initial Conditions (ICs) and Boundary Conditions
    (BCs)

21
Governing Equations (B,S, L)
(Equations based on average velocity)
Continuity
x - Equation of motion
22
Numerics / Discretization
  • Computational solution of the IBVP
  • Method dependent upon the model equations and
    physics
  • Several components to formulation
  • Discretization and linearization
  • Assembly of system of algebraic equations
  • Solve the system and get approximate solutions

23
Finite Differences
Finite difference representation
Truncation error
Methods of Solution
Direct methods
Iterative methods
Jacobi method, Gauss-Seidel Method, SOR method
Cramers Rule, Gauss elimination LU decomposition
24
Numeric Solution (Finite Differences)
jmax
j1
j
Taylors Series Expansion u i,j velocity of
fluid
j-1
o
x
i
i1
i-1
imax
Discrete Grid Points
25
CFD process
  • Geometry description
  • Specification of flow conditions and properties
  • Selection of models
  • Specification of initial and boundary conditions
  • Grid generation and transformation
  • Specification of numerical parameters
  • Flow solution
  • Post processing Analysis, and visualization

26
Geometry description
  • Typical approaches
  • Make assumptions and simplifications
  • CAD/CAE integration
  • Engineering drawings
  • Coordinates include Cartesian system (x,y,z),
    cylindrical system (r, ?, z), and spherical
    system(r, ?, F)

27
Selection of models for flow field
  • Direct Numerical Simulations (DNS) is to solve
    the N-S equations directly without any modeling.
    Grid must be fine enough to resolve all flow
    scales. Applied for laminar flow and rare be used
    in turbulent flow.
  • Reynolds Averaged Navier-Stokes (NS) equations
    (RANS) is to perform averaging of NS equations
    and establishing turbulent models for the eddy
    viscosity. Too many averaging might damping
    vortical structures in turbulent flows
  • Large Eddy Simulation (LES), Smagorinsky
    constant model and dynamic model. Provide more
    instantaneous information than RANS did.
    Instability in complex geometries
  • Detached Eddy Simulation (DES) is to use one
    single formulation to combine the advantages of
    RANS and LES.

28
CFD - how it works
  • Analysis begins with a mathematical model of a
    physical problem.
  • Conservation of matter, momentum, and energy must
    be satisfied throughout the region of interest.
  • Fluid properties are modeled empirically.
  • Simplifying assumptions are made in order to make
    the problem tractable (e.g., steady-state,
    incompressible, inviscid, two-dimensional).
  • Provide appropriate initial and boundary
    conditions for the problem.

Filling Nozzle
Bottle
Domain for bottle filling problem.
29
CFD - how it works (2)
  • CFD applies numerical methods (called
    discretization) to develop approximations of the
    governing equations of fluid mechanics in the
    fluid region of interest.
  • Governing differential equations algebraic.
  • The collection of cells is called the grid.
  • The set of algebraic equations are solved
    numerically (on a computer) for the flow field
    variables at each node or cell.
  • System of equations are solved simultaneously to
    provide solution.
  • The solution is post-processed to extract
    quantities of interest (e.g. lift, drag, torque,
    heat transfer, separation, pressure loss, etc.).

Mesh for bottle filling problem.
30
Discretization
  • Domain is discretized into a finite set of
    control volumes or cells. The discretized domain
    is called the grid or the mesh.
  • General conservation (transport) equations for
    mass, momentum, energy, etc., are discretized
    into algebraic equations.
  • All equations are solved to render flow field.

control volume
31
Design and create the grid
  • Should you use a quad/hex grid, a tri/tet grid, a
    hybrid grid, or a non-conformal grid?
  • What degree of grid resolution is required in
    each region of the domain?
  • How many cells are required for the problem?
  • Will you use adaption to add resolution?
  • Do you have sufficient computer memory?

arbitrary polyhedron
32
Tri/tet vs. quad/hex meshes
  • For simple geometries, quad/hex meshes can
    provide high-quality solutions with fewer cells
    than a comparable tri/tet mesh.
  • For complex geometries, quad/hex meshes show no
    numerical advantage, and you can save meshing
    effort by using a tri/tet mesh.

33
Hybrid mesh example
  • Valve port grid.
  • Specific regions can be meshed with different
    cell types.
  • Both efficiency and accuracy are enhanced
    relative to a hexahedral or tetrahedral mesh
    alone.

34
Dinosaur mesh example
35
Set up the numerical model
  • For a given problem, you will need to
  • Select appropriate physical models.
  • Turbulence, combustion, multiphase, etc.
  • Define material properties.
  • Fluid.
  • Solid.
  • Mixture.
  • Prescribe operating conditions.
  • Prescribe boundary conditions at all boundary
    zones.
  • Provide an initial solution.
  • Set up solver controls.
  • Set up convergence monitors.

36
Initial and boundary conditions
  • For steady/unsteady flow
  • IC should not affect final solution, only
    convergence path, i.e. iteration numbers needed
    to get the converged solution.
  • Robust codes should start most problems from very
    crude IC, . But more reasonable guess can speed
    up the convergence.
  • Boundary conditions
  • No-slip or slip-free on the wall, periodic, inlet
    (velocity inlet, mass flow rate, constant
    pressure, etc.), outlet (constant pressure,
    velocity convective, buffer zone, zero-gradient),
    and non-reflecting (compressible flows, such as
    acoustics), etc.

37
Compute the solution
  • The discretized conservation equations are solved
    iteratively. A number of iterations are usually
    required to reach a converged solution.
  • Convergence is reached when
  • Changes in solution variables from one iteration
    to the next are negligible.
  • Residuals provide a mechanism to help monitor
    this trend.
  • Overall property conservation is achieved.
  • The accuracy of a converged solution is dependent
    upon
  • Appropriateness and accuracy of the physical
    models.
  • Grid resolution and independence.
  • Problem setup.

38
Numerical parameters flow solution
  • Typical time history of residuals
  • The closer the flow field to the converged
    solution, the smaller the speed of the residuals
    decreasing.

Solution converged, residuals do not change
after more iterations
39
Post-processing
  • Analysis, and visualization
  • Calculation of derived variables
  • Vorticity
  • Wall shear stress
  • Calculation of integral parameters forces,
    moments
  • Visualization (usually with commercial software)
  • Simple X-Y plots
  • Simple 2D contours
  • 3D contour carpet plots
  • Vector plots and streamlines (streamlines are the
    lines whose tangent direction is the same as the
    velocity vectors)
  • Animations (dozens of sample pictures in a series
    of time were shown continuously)

40
Examine the results
  • Visualization can be used to answer such
    questions as
  • What is the overall flow pattern?
  • Is there separation?
  • Where do shocks, shear layers, etc. form?
  • Are key flow features being resolved?
  • Are physical models and boundary conditions
    appropriate?
  • Numerical reporting tools can be used to
    calculate quantitative results, e.g
  • Lift, drag, and torque.
  • Average heat transfer coefficients.
  • Surface-averaged quantities.

41
Velocity vectors around a dinosaur
42
Velocity magnitude (0-6 m/s) on a dinosaur
43
Pressure field on a dinosaur
44
Advantages of CFD
  • Relatively low cost.
  • Using physical experiments and tests to get
    essential engineering data for design can be
    expensive.
  • CFD simulations are relatively inexpensive, and
    costs are likely to decrease as computers become
    more powerful.
  • Speed.
  • CFD simulations can be executed in a short period
    of time.
  • Quick turnaround means engineering data can be
    introduced early in the design process.
  • Ability to simulate real conditions.
  • Many flow and heat transfer processes can not be
    (easily) tested, e.g. hypersonic flow.
  • CFD provides the ability to theoretically
    simulate any physical condition.

45
Limitations of CFD
  • Physical models.
  • CFD solutions rely upon physical models of real
    world processes (e.g. turbulence,
    compressibility, chemistry, multiphase flow,
    etc.).
  • The CFD solutions can only be as accurate as the
    physical models on which they are based.
  • Numerical errors.
  • Solving equations on a computer invariably
    introduces numerical errors.
  • Round-off error due to finite word size
    available on the computer. Round-off errors will
    always exist (though they can be small in most
    cases).
  • Truncation error due to approximations in the
    numerical models. Truncation errors will go to
    zero as the grid is refined. Mesh refinement is
    one way to deal with truncation error.

46
Limitations of CFD (2)
  • Boundary conditions.
  • As with physical models, the accuracy of the CFD
    solution is only as good as the initial/boundary
    conditions provided to the numerical model.
  • Example flow in a duct with sudden expansion. If
    flow is supplied to domain by a pipe, you should
    use a fully-developed profile for velocity rather
    than assume uniform conditions.

47
Software and resources
  • CFD software was built upon physics, modeling,
    numerics.
  • Two types of available software
  • Commercial (e.g., FLUENT, CFX, Star-CD)
  • Research (e.g., CFDSHIP-IOWA, U2RANS)
  • More information on CFD can be got on the
    following website
  • CFD Online http//www.cfd-online.com/
  • CFD software
  • FLUENT http//www.fluent.com/
  • CFDRC http//www.cfdrc.com/
  • Computational Dynamics http//www.cd.co.uk/
  • CFX/AEA http//www.software.aeat.com/cfx/
  • Grid generation software
  • Gridgen http//www.pointwise.com
  • GridPro http//www.gridpro.com/
  • Hypermesh
  • Visualization software
  • Tecplot http//www.amtec.com/
  • Fieldview http//www.ilight.com/

48
THANK YOU
About PowerShow.com