# Low Speed Airfoil

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 December 15, 2004, 05:01 Low Speed Airfoil #1 Mancusi Guest   Posts: n/a 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.

 December 15, 2004, 08:11 Re: Low Speed Airfoil #2 Mark Guest   Posts: n/a Hi The force coefficients are calculated using the reference values (Area, density & velocity) set in the report menu. Have you set these? Mark

 December 15, 2004, 10:02 Re: Low Speed Airfoil #3 mateus Guest   Posts: n/a 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 low-Re model bu the discrepancies will remain. mateus

 December 16, 2004, 11:04 Re: Low Speed Airfoil #4 Mancusi Guest   Posts: n/a I use these settings FLUENT Version: 2d, dp, coupled imp, S-A (2d, double precision, coupled implicit, Spalart-Allmaras) Release: 6.1.22 Title: Models ------ Model Settings -------------------------------------------------------------- Space 2D Time Steady Viscous Spalart-Allmaras 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 pressure-far-field airfoil 4 wall default-interior 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 X-Velocity Of Zone 0 Y-Velocity Of Zone 0 Rotation speed 0 X-Origin of Rotation-Axis 0 Y-Origin of Rotation-Axis 0 Deactivated Thread no Laminar zone? no Set Turbulent Viscosity to zero within laminar zone? yes Porous zone? no X-Component of Direction-1 Vector 1 Y-Component of Direction-1 Vector 0 Direction-1 Viscous Resistance 0 Direction-2 Viscous Resistance 0 Direction-1 Inertial Resistance 0 Direction-2 Inertial Resistance 0 C0 Coefficient for Power-Law 0 C1 Coefficient for Power-Law 0 Porosity 1 Solid Material Name aluminum farfield Condition Value --------------------------------------------- Gauge Pressure 101325 Mach Number 0.028999999 Temperature 300 X-Component of Flow Direction 1 Y-Component 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 X-Component of Wall Translation 1 Y-Component of Wall Translation 0 Define wall velocity components? no X-Component of Wall Translation 0 Y-Component of Wall Translation 0 External Emissivity 1 External Radiation Temperature 300 Wall Roughness Height 0 Wall Roughness Constant 0.5 Rotation Speed 0 X-Position of Rotation-Axis Origin 0 Y-Position of Rotation-Axis Origin 0 X-component of shear stress 0 Y-component of shear stress 0 Surface tension gradient 0 default-interior 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 F-Cycle 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 ideal-gas #f Cp (Specific Heat) j/kg-k constant 1006.43 Thermal Conductivity w/m-k constant 0.0242 Viscosity kg/m-s constant 1.7894001e-05 Molecular Weight kg/kgmol constant 28.966 L-J Characteristic Length angstrom constant 3.711 L-J 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/kg-k constant 871 Thermal Conductivity w/m-k constant 202.4

 December 16, 2004, 11:15 Re: Low Speed Airfoil #5 Mancusi Guest   Posts: n/a How do I set it to use low-Re

 December 17, 2004, 02:40 Re: Low Speed Airfoil #6 Charles Guest   Posts: n/a 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.

 December 17, 2004, 10:45 Re: Low Speed Airfoil #7 Mancusi Guest   Posts: n/a I am aware of this and do compensate for it but I run at 0 degrees so it cant be a problem

 April 3, 2014, 06:11 #8 New Member   Join Date: Apr 2013 Posts: 4 Rep Power: 5 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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