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Advanced CFD Analysis of Aerodynamics Using CFX

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Title: Advanced CFD Analysis of Aerodynamics Using CFX


1
Advanced CFD Analysis ofAerodynamics Using CFX
  • Jorge Carregal Ferreira
  • Achim Holzwarth, Florian Menter

2
Outline
  • CFX Advanced CFD software
  • The company
  • The products
  • Turbulence Modells in CFX
  • Near wall treatment in CFX
  • Examples
  • Duct with adverse pressure gradient
  • Airfoils
  • Heat transfer

3
CFX Member of AEA Technology
4
CFX Global Position
  • CFD (Computational Fluid Dynamics) group of AEA
    Technology
  • Largest European CFD company
  • 210 employees
  • 8 main offices
  • Strong industrial presence
  • Growth rate approx. 25 per year
  • More than 1500 installed licenses

5
CFD-Analysis
  • Generate geometry fluid domain
  • Generate mesh discrete representation of fluid
    domain
  • Solve Navier-Stokes Equiations
  • Analyse Results
  • Coupling Optimisation, fluid-structure coupling,
    accoustic analysis, design improvements

6
Leading Technology in CFX-5
  • Easy to use
  • Pre-Processor CFX-Build based on MSC.Patran
  • Unstructured hybrid grids
  • Coupled algebraic multigrid-solver (AMG)
    Accurate, robust and fast
  • Solution time scales linear with grid size
  • Excellent parallel performance
  • Grid adaptation
  • UNIX, NT, Linux

7
Leading Technology in CFX-5
  • Laminar and turbulent flows.
  • Stationary and transient solutions.
  • Large variaty of turbulence models.
  • Transport equations for additional scalars.
  • Multi-component and multi-phase fluids.
  • Coupling with solid heat conduction.
  • Solution depended mesh adaptation.
  • Linear scaling of solver with grid size.
  • Scalable parallel performance.

8
Preprocessing with CFX-Build
Geometry modeller based On MSC.Patran Native CAD
interfaces Pro/Engineer, CATIA, Unigraphics,
IDEAS, etc.
9
Turbulence Models in CFX-5
  • Release of the latest turbulence models
  • k-? Model Variants
  • k-? Model and BSL Model (Wilcox, Menter)
  • SST Model (Menter, Blending between k-? and k-?)
  • Reynolds Stress Models
  • Extended near-wall treatments
  • Scalable wall functions for k-?
  • Automatic near-wall treatment for k-? and SST
  • LES model (Smagorinski)
  • Documented validation cases on these models are
    available
  • Future Improved LES and transition modelling

10
Problems of Standard k-? Model
  • Two Problems
  • Missing transport effects.
  • Too large length scales.
  • Result
  • Reduced or omitted separation.
  • Very often Too optimistic machine performance.

11
Standard k-? Model (Wilcox)
12
Standard k-? Model (Wilcox)
  • Advantages
  • Lower length scales near wall.
  • Robust sublayer formulation (low-Re).
  • Problem
  • Free stream sensitivity.
  • Has not replaced k-? models.

13
k-? Model Free Stream Problem
Change of w in freestream
Eddy viscosity profile
Velocity profile
14
k-? vs. k-? Formulation
15
Optimal Two Equation Model
  • Combination of k-w and k-e model
  • k-w model near the surface
  • k-e model for free shear flows (e equation is
    transformed to w)
  • Blending is performed automatically based on
    solution and distance from the surface.
  • This model is called Baseline Model BSL
  • Combined with Shear-Stress-Transport limiter
    offers optimal boundary layer simulation
    capabilities.
  • BSLLimiter gives SST model.

16
Diffuser Flow, 1
Experiment Gersten et al.
17
Diffuser Flow, 2
18
Wall Boundary Treatment
Standard wall function boundary conditions are
the single most limiting factor in industrial CFD
computations regarding accuracy!
y has to be between 25 and 500 type
statements are problematic!
  • Boundary layer resolution requirements have to be
    satisfied.
  • Log. Profile assumptions have to be satisfied.
  • To satisfy both at the same time is the
    challenge.

19
Scaling of Variables near Wall
20
Flat Plate Velocity Profile
Intersection
Finer Grids
Standard Wall Function
New Wall Function
21
Flate Plate Wall Friction
Finer Grids
Finer Grids
Standard Wall Function
New Wall Function
22
Low-Re k-? Model
  • Viscous sublayer resolution.
  • Simple formulation.
  • Numerically robust.
  • Grid resolution near wall ylt1-2.
  • Improved adverse pressure gradient behaviour.
  • Non-trivial boundary conditions.
  • Free stream dependency problem.
  • Blending possible.

23
k-? Automatic Switch
24
k-? Automatic Switch
25
Pipe Expansion with Heat Transfer
Structured Grid (150.000 nodes) Reynolds Number
ReD 23210 Fully Developed Turbulent Flow at
Inlet Experiments by Baughn et al. (1984)
26
Pipe Expansion with Heat Transfer
k-? Model, Standard Wall Functions
27
Pipe Expansion with Heat Transfer
SST Model, Low-Re Wall Treatment
28
Pipe Expansion with Heat Transfer
SST Model, Automatic Wall Treatment
29
Summary
  • CFX Advanced CFD software
  • Fast and robust solver technology
  • Powerful Pre- and Postprocessing tools
  • Leading Turbulence Modells
  • Robust near wall treatment
  • Allows for
  • Accurate solutions
  • Reliable Predictions

30
Thank you!
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