[ap79]

Hello,
I am trying to use Floworks to evaluate the lift and drag coefficients of an airfoil. While the computed lift coefficients match more or less the expected values, the computed drag coefficients are much higher than the expected ones (>2 x the expected ones).
Is Floworks suited to do that sort of computations?
If yes and if i post the details of my calculation setups, can someone help me to find out what I am doing wrong?
Thanks!

[Boris_M]

Yes, it is possible to do such simulations. The important thing is a correct meshing and solver selection (eventually high mach number option) depending on your flow velocity etc.

Boris

[ap79]

Hello Boris, thank you for your reply.
The simulation setup is pasted below. I have attached an image of the initial mesh around the airfoil and another one showing the mesh after a level 3 refinement during the computation.
I've got a glide ratio Fw/Fa = 0,055, which is far too high given the high Reynolds number (>10^6).
I have tried other setups before, but the results were even worse. I can't really figure out how to fix that.



INPUT DATA

Initial Mesh Settings
Automatic initial mesh: Off

Basic Mesh Dimensions
Number of cells in X: 121
Number of cells in Y: 77
Number of cells in Z: 1

Control Planes
Control planes in X direction
Name Minimum Maximum Number of cells Ratio
X1 -1.850 -0.175 - 6.4238891
X2 -0.175 0.035 - 1.0000000
X3 0.035 0.381 - 1.0000000
X4 0.381 2.750 - 0.1150187
Control planes in Y direction
Name Minimum Maximum Number of cells Ratio
Y1 -1.250 -0.047 - 5.5625441
Y2 -0.047 -0.010 - 1.0000000
Y3 -0.010 0.027 - 1.0000000
Y4 0.027 1.150 - 0.1902753
Control planes in Z direction
Name Minimum Maximum Number of cells Ratio
Z1 -0.001 0.001 - 1.0000000

Solid/Fluid Interface
Small solid features refinement level: 7
Curvature refinement level: 7
Curvature refinement criterion: 0.010 rad
Tolerance refinement level: 7
Tolerance refinement criterion: 0.001 m

Refining cells
Refine fluid cells: Off
Refine partial cells: Off
Refine solid cells: Off

Narrow Channels
Advanced narrow channel refinement: On
Characteristic number of cells across a narrow channel: 5
Narrow channels refinement level: 7
The minimum height of narrow channels: Off
The maximum height of narrow channels: Off

Computational Domain

Size
X min: -1.850 m
X max: 2.750 m
Y min: -1.250 m
Y max: 1.150 m
Z min: -0.001 m
Z max: 0.001 m

Boundary Conditions
2D plane flow: XY - plane flow
At X min: Default
At X max: Default
At Y min: Default
At Y max: Default
At Z min: Symmetry
At Z max: Symmetry

Physical Features
Heat conduction in solids: Off
Time dependent: On
Gravitational effects: Off
Flow type: Laminar and turbulent
Cavitation: Off
High Mach number flow: Off
Default roughness: 0 micrometer
Default wall conditions: Adiabatic wall

Ambient Conditions

Thermodynamic parameters
Static Pressure: 101325.00 Pa
Temperature: 283.00 K

Velocity parameters
Velocity vector
Velocity in X direction: 9.650 m/s
Velocity in Y direction: 0 m/s
Velocity in Z direction: 0 m/s

Turbulence parameters
Turbulence intensity and length
Intensity: 0.10 %
Length: 1.000e-004 m

Material Settings

Fluids
Water

Goals

Global Goals

GG Min Static Pressure
Type: Global Goal
Goal type: Static Pressure
Calculate: Minimum value
Coordinate system: Global coordinate system
Criteria: 100.00 Pa
Use in convergence : On

GG Av Density (Fluid)
Type: Global Goal
Goal type: Density (Fluid)
Calculate: Average value
Coordinate system: Global coordinate system
Criteria: 100.00 kg/m^3
Use in convergence : On

GG Max Velocity
Type: Global Goal
Goal type: Velocity
Calculate: Maximum value
Coordinate system: Global coordinate system
Criteria: 0.010 m/s
Use in convergence : On

GG Force (X)
Type: Global Goal
Goal type: Force (X)
Coordinate system: Global coordinate system
Criteria: 1.000 N
Use in convergence : On

GG Force (Y)
Type: Global Goal
Goal type: Force (Y)
Coordinate system: Global coordinate system
Criteria: 1.000 N
Use in convergence : On

Equation Goals

Za
Type: Equation Goal
Formula: GG Force (Y) *2/1000/9,65/9,65/0,378/0,002
Dimensionality: No units
Criteria: 0.0001000
Use in convergence : On

Zw
Type: Equation Goal
Formula: GG Force (X) *2/1000/9,65/9,65/0,378/0,002
Dimensionality: No units
Criteria: 1.0000000e-005
Use in convergence : On

tanL
Type: Equation Goal
Formula: GG Force (X) /GG Force (Y)
Dimensionality: No units
Criteria: 1.0000000e-008
Use in convergence : On

Calculation Control Options

Finish Conditions
Finish conditions: If one is satisfied

Goals convergence
Analysis interval: 3e-001

Solver Refinement
Refinement: Disabled

Results Saving
Save before refinement: On

Advanced Control Options

Flow Freezing
Flow freezing strategy: Disabled
Manual time step (Freezing): Off
Manual time step: 0.003 s



mesh1.jpg

mesh after refinement.jpg

[Boris_M]

Yes, that's not a good way of setting a project up for such an application. Don't use small feature refinement like that. Also use more local meshes and don't change the angle of the airfoil but use the capability of defining the aerodynamic angle in the initial conditions of the project.
If you send me your email address in a private message I can send you some more information and examples.

Boris

[ap79]

Hello,
adjusting the computational domain size and he mesh has actually shown to be crucial to obtaining realistic results. In the simulation setup pasted below, as suggested by Boris docs, the computational domain size is more than 20 times larger than the chord length in each direction. A local mesh around the airfoil has been shaped like in the attached image.
The "aerodynamic angles" feature of FW 2014 has been used (velocity: 9,65 m/s; angle of attack: 5°)


INPUT DATA

Initial Mesh Settings
Automatic initial mesh: On
Result resolution level: 6
Advanced narrow channel refinement: On
Refinement in solid region: Off

Geometry Resolution
Evaluation of minimum gap size: Automatic
Evaluation of minimum wall thickness: Automatic

Local Mesh Settings

Mesh locale
Components: Mesh locale-1

Solid/fluid interface
Small solid features refinement level: 3
Curvature refinement level: 3
Curvature refinement criterion: 0.100 rad
Tolerance refinement level: 3
Tolerance refinement criterion: 0.010 m

Refining cells
Refine all cells: On
Level of refining all cells : 0

Narrow channels
Advanced narrow channel refinement: On
Characteristic number of cells across a narrow channel: 14
Narrow channels refinement level: 3
The minimum height of narrow channels: Off
The maximum height of narrow channels: Off

Computational Domain

Size
X min: -10.000 m
X max: 15.000 m
Y min: -15.000 m
Y max: 10.000 m
Z min: -0.001 m
Z max: 0.001 m

Boundary Conditions
2D plane flow: XY - plane flow
At X min: Default
At X max: Default
At Y min: Default
At Y max: Default
At Z min: Symmetry
At Z max: Symmetry

Physical Features
Heat conduction in solids: Off
Time dependent: Off
Gravitational effects: Off
Flow type: Laminar and turbulent
Cavitation: Off
High Mach number flow: Off
Default roughness: 0 micrometer
Default wall conditions: Adiabatic wall

Ambient Conditions

Thermodynamic parameters
Static Pressure: 101325.00 Pa
Temperature: 283.00 K

Velocity parameters
Velocity vector
Velocity in X direction: 9.650 m/s
Velocity in Y direction: 0 m/s
Velocity in Z direction: 0 m/s

Turbulence parameters
Turbulence intensity and length
Intensity: 0.10 %
Length: 1.000e-004 m

Material Settings

Fluids
Water

Goals

Global Goals

GG Min Static Pressure
Type: Global Goal
Goal type: Static Pressure
Calculate: Minimum value
Coordinate system: Global coordinate system
Criteria: 100.00 Pa
Use in convergence : On

GG Av Density (Fluid)
Type: Global Goal
Goal type: Density (Fluid)
Calculate: Average value
Coordinate system: Global coordinate system
Criteria: 100.00 kg/m^3
Use in convergence : On

GG Max Velocity
Type: Global Goal
Goal type: Velocity
Calculate: Maximum value
Coordinate system: Global coordinate system
Criteria: 0.010 m/s
Use in convergence : On

GG Force (X)
Type: Global Goal
Goal type: Force (X)
Coordinate system: Sistema di riferimento pala
Criteria: 1.000 N
Use in convergence : On

GG Force (Y)
Type: Global Goal
Goal type: Force (Y)
Coordinate system: Sistema di riferimento pala
Criteria: 1.000 N
Use in convergence : On

Equation Goals

Za
Type: Equation Goal
Formula: GG Force (Y) *2/1000/9,66/9,66/0,39/0,002
Dimensionality: No units
Criteria: 0.0001000
Use in convergence : On

Zw
Type: Equation Goal
Formula: GG Force (X) *2/1000/9,66/9,66/0,39/0,002
Dimensionality: No units
Criteria: 1.0000000e-005
Use in convergence : On

tanL
Type: Equation Goal
Formula: GG Force (X) /GG Force (Y)
Dimensionality: No units
Criteria: 1.0000000e-008
Use in convergence : On

Calculation Control Options

Finish Conditions
Finish conditions: If one is satisfied

Goals convergence
Analysis interval: 5e-001

Solver Refinement
Refinement: Disabled

Results Saving
Save before refinement: On

Advanced Control Options

Flow Freezing
Flow freezing strategy: Disabled