Low Speed Airfoil
I can't get make any sense of the drag,lift and momentum coef's that I get when modelling a low speed airfoil. I want to model the DAE11 airfoil at 10m/s.
I've created a circular mesh with diameter 20 meters in the middle is the airfoil with a chord of 1 meter. I have a very fine boundary layer and a very fine mesh around the airfoil. I set the circular edge to be a pressure farfield (which I can change to a velocity inlet in FLUENT afterwards) and the upper and lower parts of the airfoil as one wall. The airfoil is almost completely laminar so I should get good result running it in laminar solver. The pressure graph over the airfoil matches in shape and so do the pressure fields near the airfoil when I dsiplay them, just like you would epext them to be over an airfoil only the coef's dont make any sense. I've run my problem with different turbulence model to and applied all the obvious settings. Can anybody please help me I'm stuck. 
Re: Low Speed Airfoil
Hi
The force coefficients are calculated using the reference values (Area, density & velocity) set in the report menu. Have you set these? Mark 
Re: Low Speed Airfoil
Hi!
Also it is common that pressure and lift coeficient are in good agreement wit exp. data. On the other hand the drag coef. is usually overpredicted. the reason lies in bad simulation in boundary layer flow. It usually helps a bit to use lowRe model bu the discrepancies will remain. mateus 
Re: Low Speed Airfoil
I use these settings
FLUENT Version: 2d, dp, coupled imp, SA (2d, double precision, coupled implicit, SpalartAllmaras) Release: 6.1.22 Title: Models  Model Settings  Space 2D Time Steady Viscous SpalartAllmaras turbulence model Production Option Vorticity Heat Transfer Enabled Solidification and Melting Disabled Radiation None Species Transport Disabled Coupled Dispersed Phase Disabled Pollutants Disabled Soot Disabled Boundary Conditions  Zones name id type  fluid 2 fluid farfield 3 pressurefarfield airfoil 4 wall defaultinterior 6 interior Boundary Conditions fluid Condition Value  Material Name air Specify source terms? no Source Terms () Specify fixed values? no Fixed Values () Motion Type 0 XVelocity Of Zone 0 YVelocity Of Zone 0 Rotation speed 0 XOrigin of RotationAxis 0 YOrigin of RotationAxis 0 Deactivated Thread no Laminar zone? no Set Turbulent Viscosity to zero within laminar zone? yes Porous zone? no XComponent of Direction1 Vector 1 YComponent of Direction1 Vector 0 Direction1 Viscous Resistance 0 Direction2 Viscous Resistance 0 Direction1 Inertial Resistance 0 Direction2 Inertial Resistance 0 C0 Coefficient for PowerLaw 0 C1 Coefficient for PowerLaw 0 Porosity 1 Solid Material Name aluminum farfield Condition Value  Gauge Pressure 101325 Mach Number 0.028999999 Temperature 300 XComponent of Flow Direction 1 YComponent of Flow Direction 0 Turbulence Specification Method 0 Modified Turbulent Viscosity 0.001 Turbulence Intensity 0.1 Turbulence Length Scale 1 Hydraulic Diameter 1 Turbulent Viscosity Ratio 10 airfoil Condition Value  Wall Thickness 0 Heat Generation Rate 0 Material Name aluminum Thermal BC Type 1 Temperature 300 Heat Flux 0 Convective Heat Transfer Coefficient 0 Free Stream Temperature 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 0 XComponent of Wall Translation 1 YComponent of Wall Translation 0 Define wall velocity components? no XComponent of Wall Translation 0 YComponent of Wall Translation 0 External Emissivity 1 External Radiation Temperature 300 Wall Roughness Height 0 Wall Roughness Constant 0.5 Rotation Speed 0 XPosition of RotationAxis Origin 0 YPosition of RotationAxis Origin 0 Xcomponent of shear stress 0 Ycomponent of shear stress 0 Surface tension gradient 0 defaultinterior Condition Value  Solver Controls  Equations Equation Solved  Flow yes Modified Turbulent Viscosity yes Numerics Numeric Enabled  Absolute Velocity Formulation yes Relaxation Variable Relaxation Factor  Modified Turbulent Viscosity 0.80000001 Turbulent Viscosity 1 Solid 1 Linear Solver Solver Termination Residual Reduction Variable Type Criterion Tolerance  Flow FCycle 0.1 Modified Turbulent Viscosity Flexible 0.1 0.7 Discretization Scheme Variable Scheme  Flow Second Order Upwind Modified Turbulent Viscosity Second Order Upwind Time Marching Parameter Value  Solver Implicit Courant Number 5 Solution Limits Quantity Limit  Minimum Absolute Pressure 1 Maximum Absolute Pressure 5000000 Minimum Temperature 1 Maximum Temperature 5000 Maximum Turb. Viscosity Ratio 100000 Material Properties  Material: air (fluid) Property Units Method Value(s)  Density kg/m3 idealgas #f Cp (Specific Heat) j/kgk constant 1006.43 Thermal Conductivity w/mk constant 0.0242 Viscosity kg/ms constant 1.7894001e05 Molecular Weight kg/kgmol constant 28.966 LJ Characteristic Length angstrom constant 3.711 LJ Energy Parameter k constant 78.6 Thermal Expansion Coefficient 1/k constant 0 Degrees of Freedom constant 0 Material: aluminum (solid) Property Units Method Value(s)  Density kg/m3 constant 2719 Cp (Specific Heat) j/kgk constant 871 Thermal Conductivity w/mk constant 202.4 
Re: Low Speed Airfoil
How do I set it to use lowRe

Re: Low Speed Airfoil
Are you aware that Fluent's Lift and drag coefficients are given in body axes, not wind axes? So if you are changing the angle of the incoming flow, the calculated lift and drag forces are actually normal and axial forces. Also, by default, moments are taken about 0,0,0 , but you can set this.

Re: Low Speed Airfoil
I am aware of this and do compensate for it but I run at 0 degrees so it cant be a problem

Hai Charles, here to ask if we are not changing the angle of the incoming flow(constant flow), but change the angle of object (yaw), the Fluent's Lift and drag coefficients given are in body axes or wind axes?
Thanks,Regards wcchan2. 
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