[hssnjfry]

hi
Do airfoil drag coefficient is changed by changing the dimensions?
If the answer is yes, there is a relationship between the two( drag & dimension)?
tanks

[fluid23]

Drag should only change with Reynolds number, so if you increase the airfoil without increasing the velocity to keep Re constant, then yes. Your drag will increase.

[fluid23]

Depending on the airfoil you are using you may be able to find a chart that shows Cdo vs Re. As far as I can recall, there isn't an equation that can be applied.

I should clarify. Drag coefficient will not change with constant Re. The magnitude of the force vector will however increase due to larger chord and greater dynamic pressure. However, when non-dimensionalized to Cd it will remain constant.

Re=rho*V*c/mu

Drag=1/2*rho*V^2*c*Cd

[hssnjfry]

In fact, I have the results of an airfoil in a wind tunnel, and it got Fluent models with different sizes and different drag coefficient obtained results are compared with each other on this basis I wonder whether this difference is due to dimensional change

[fluid23]

just look at your experimental data for that. considering CFD data to look at the effect of increasing your chord is unecessary. Do you have test data at same velocity, different chords? It should be easy to quantify what you are after if so.

[hssnjfry]

View all testing in the wind tunnel simulations in FLUENT is intended as speed, pressure and angle of attack, but the value obtained for the drag coefficient is very different

[fluid23]

Correlating wind tunnel and CFD can be quite challenging even under the best of circumstances. What kind of analysis are you running? What is your turbulence model and wall treatment? Also, what is your current cell count?

[hssnjfry]

i used this link for solver and other seting

[fluid23]

It wants me to sign up to view that document. I am not going to do that. Can you just tell me?

[hssnjfry]

model:viscous
viscous model:k-omega
k-omega model:sst
density:ideal gas,viscousity for gas:sutherland
wall:no slip

[fluid23]

That's a start. So a RANS analysis, 2 equation model. K-w SST is a good choice.

By wall treatment I was refering to how the turbulence model handles near wall cells. It will either be near wall, far wall or maybe all wall y+. Each has its own requirements for y+ values. What type of mesh is this? 2D or 3D? Structured, tet, quad, poly? What is your current cell count and domain size with respect to airfoil chord?

Also, what are the y+ values at the airfoil surface? Are your residuals converged? Are your lift and drag values converged?

[hssnjfry]

Model Settings
---------------------------------------------------------
Space 2D
Time Steady
Viscous SST k-omega turbulence model
Heat Transfer Enabled
Solidification and Melting Disabled
Radiation None
Species Disabled
Coupled Dispersed Phase Disabled
NOx Pollutants Disabled
SOx Pollutants Disabled
Soot Disabled
Mercury Pollutants Disabled

Material Properties
-------------------

Material: air (fluid)

Property Units Method Value(s)
----------------------------------------------------------------------------------
Density kg/m3 ideal-gas #f
Cp (Specific Heat) j/kg-k constant 1006.43
Thermal Conductivity w/m-k constant 0.0242
Viscosity kg/m-s sutherland (1.716e-05 273.11 110.56 )
Molecular Weight kg/kgmol constant 28.966
Thermal Expansion Coefficient 1/k constant 0
Speed of Sound m/s none #f

Material: aluminum (solid)

Property Units Method Value(s)
---------------------------------------------------
Density kg/m3 constant 2719
Cp (Specific Heat) j/kg-k constant 871
Thermal Conductivity w/m-k constant 202.4

Cell Zone Conditions
--------------------

Zones

name id type
-------------------------------
solid-surface_body 3 fluid

Setup Conditions

solid-surface_body

Condition Value
----------------------------------------------------------------------------------------------------------------------------------------------------------
Material Name air
Specify source terms? no
Source Terms ((mass) (x-momentum) (y-momentum) (k) (omega) (energy))
Specify fixed values? no
Fixed Values ((k (inactive . #f) (constant . 0) (profile )) (omega (inactive . #f) (constant . 0) (profile )))
Frame Motion? no
Relative To Cell Zone -1
Reference Frame Rotation Speed (rad/s) 0
Reference Frame X-Velocity Of Zone (m/s) 0
Reference Frame Y-Velocity Of Zone (m/s) 0
Reference Frame X-Origin of Rotation-Axis (m) 0
Reference Frame Y-Origin of Rotation-Axis (m) 0
Reference Frame User Defined Zone Motion Function none
Mesh Motion? no
Relative To Cell Zone -1
Moving Mesh Rotation Speed (rad/s) 0
Moving Mesh X-Velocity Of Zone (m/s) 0
Moving Mesh Y-Velocity Of Zone (m/s) 0
Moving Mesh X-Origin of Rotation-Axis (m) 0
Moving Mesh Y-Origin of Rotation-Axis (m) 0
Moving Mesh User Defined Zone Motion Function none
Deactivated Thread no
Laminar zone? no
Set Turbulent Viscosity to zero within laminar zone? yes
Embedded Subgrid-Scale Model 0
Momentum Spatial Discretization 0
Cwale 0.325
Cs 0.1
Porous zone? no
X-Component of Direction-1 Vector 1
Y-Component of Direction-1 Vector 0
Direction-1 Viscous Resistance (1/m2) 0
Direction-2 Viscous Resistance (1/m2) 0
Direction-1 Inertial Resistance (1/m) 0
Direction-2 Inertial Resistance (1/m) 0
C0 Coefficient for Power-Law 0
C1 Coefficient for Power-Law 0
Porosity 1
Equilibrium Thermal Model (if no, Non-Equilibrium)? yes
Non-Equilibrium Thermal Model? no
Solid Material Name aluminum
Interfacial Area Density (1/m) 1
Heat Transfer Coefficient (w/m2-k) 1

Boundary Conditions
-------------------

Zones

name id type
--------------------------------------------
pressure_far_field 6 pressure-far-field
airfoil 13 wall

Setup Conditions

pressure_far_field

Condition Value
---------------------------------------------
Gauge Pressure (pascal) 73048
Mach Number 0.4
Temperature (k) 283.24
X-Component of Flow Direction 1
Y-Component of Flow Direction 0
X-Component of Axis Direction 1
Y-Component of Axis Direction 0
Z-Component of Axis Direction 0
X-Coordinate of Axis Origin (m) 0
Y-Coordinate of Axis Origin (m) 0
Z-Coordinate of Axis Origin (m) 0
Turbulent Specification Method 2
Turbulent Kinetic Energy (m2/s2) 1
Specific Dissipation Rate (1/s) 1
Turbulent Intensity (%) 0.99999998
Turbulent Length Scale (m) 1
Hydraulic Diameter (m) 1
Turbulent Viscosity Ratio 1

airfoil

Condition Value
-------------------------------------------------------------
Wall Thickness (m) 0
Heat Generation Rate (w/m3) 0
Material Name aluminum
Thermal BC Type 1
Temperature (k) 300
Heat Flux (w/m2) 0
Convective Heat Transfer Coefficient (w/m2-k) 0
Free Stream Temperature (k) 300
Wall Motion 0
Shear Boundary Condition 0
Define wall motion relative to adjacent cell zone? yes
Apply a rotational velocity to this wall? no
Velocity Magnitude (m/s) 0
X-Component of Wall Translation 1
Y-Component of Wall Translation 0
Define wall velocity components? no
X-Component of Wall Translation (m/s) 0
Y-Component of Wall Translation (m/s) 0
External Emissivity 1
External Radiation Temperature (k) 300
Wall Roughness Height (m) 0
Wall Roughness Constant 0.5
Rotation Speed (rad/s) 0
X-Position of Rotation-Axis Origin (m) 0
Y-Position of Rotation-Axis Origin (m) 0
X-component of shear stress (pascal) 0
Y-component of shear stress (pascal) 0
Fslip constant 0
Eslip constant 0
Surface tension gradient (n/m-k) 0
Specularity Coefficient 0
Convective Augmentation Factor 1

Solver Settings
---------------

Equations

Equation Solved
-------------------
Flow yes
Turbulence yes

Numerics

Numeric Enabled
---------------------------------------
Absolute Velocity Formulation yes

Relaxation

Variable Relaxation Factor
---------------------------------------------
Turbulent Kinetic Energy 0.8
Specific Dissipation Rate 0.8
Turbulent Viscosity 1
Solid 1

Linear Solver

Solver Termination Residual Reduction
Variable Type Criterion Tolerance
-----------------------------------------------------------------------
Flow F-Cycle 0.1
Turbulent Kinetic Energy Flexible 0.1 0.7
Specific Dissipation Rate Flexible 0.1 0.7

Discretization Scheme

Variable Scheme
-----------------------------------------------
Flow Second Order Upwind
Turbulent Kinetic Energy Second Order Upwind
Specific Dissipation Rate Second Order Upwind

Time Marching

Parameter Value
-------------------------
Solver Implicit
Courant Number 5

Solution Limits

Quantity Limit
---------------------------------------
Minimum Absolute Pressure 1
Maximum Absolute Pressure 5e+10
Minimum Temperature 1
Maximum Temperature 5000
Minimum Turb. Kinetic Energy 1e-14
Minimum Spec. Dissipation Rate 1e-20
Maximum Turb. Viscosity Ratio 100000

[hssnjfry]

y+
min=8.2e-07
max=7.1e-06

[fluid23]

Whoa!!! Information overload!

Also, that only answers the 2D vs 3D question.

[fluid23]

You are only considering y+ at the airfoil surface right? Those seem too small. If you are using near wall treatment you should have values closer to 1. This could very easily screw up your drag calculations.

[hssnjfry]

Thanks for the help
check this item

[hssnjfry]

I've reviewed your guide Ansys items related to Y+, but noted that this item should be the same amount of turbulence to scrutiny and analysis on the airfoil 0012 is a test and achieved good results.
I am investigating 65-212 airfoil. The experimental results in 1952 by NASA. But the results are very different aerodynamic coefficients Fluent me. For example, the drag coefficient in the picture are the results of wind tunnel.

For example, the drag coefficient results at Mach 0.8 and Fluent to 8 degrees angle of attack against 1.11901e-02 is very different from the wind tunnel

[hssnjfry]

Guides used
http://hsc.hsu.ac.ir/index.php/apps/...%20Airfoil.pdf

http://hsc.hsu.ac.ir/index.php/apps/...ca-tn-2670.pdf

http://hsc.hsu.ac.ir/index.php/apps/...iles=tut03.pdf