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Hello guys, I am trying to study the flow around NACA0012 airfoil at zero angle of attack. However, when I try to refine the octree parameter around the airfoil and generate the mesh, every single time I get different values for Lift force! Any reasons??

hossam
Hello guys, I am trying to study the flow around NACA0012 airfoil at zero angle of attack. However, when I try to refine the octree parameter around the airfoil and generate the mesh, every single time I get different values for Lift force! Any reasons??
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    Hello hassam,
     
    I think it is very difficult to get an exact value of zero as a solution for numerical calculations.
    Whether it can be regarded as zero or not does not depend on its absolute value, but on the problem.
     
    How about comparing it with the case of angle of attack, which is not zero as the lift coefficient?
    I will attach the results of my test below.
    0deg_vs_2deg
    In the case of 0 degree angle of attack, CL values are depending on the octant.
    In some cases, even the signs are different.
    On the other hand, for 2 degrees angle of attack, the dependence on the octant is small and  CL values are close to the experimental value.
    CL values at 0 degrees angle of attack are sufficiently small compared to CL values at 2 degrees angle of attack that they can be regarded as zero.
     
    By the way, regarding the boundary layer, I think it is essential to set up the boundary layer element in order to obtain highly accurate results.
    This is especially effective for problems where the viscous stress acting on the wall surface has a significant effect on the calculation results.
    For airfoil type problems, I recommend inserting about 10 layers of boundary layers.
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  • 0
    Hello hassam,
     
    I think it is very difficult to get an exact value of zero as a solution for numerical calculations.
    Whether it can be regarded as zero or not does not depend on its absolute value, but on the problem.
     
    How about comparing it with the case of angle of attack, which is not zero as the lift coefficient?
    I will attach the results of my test below.
    0deg_vs_2deg
    In the case of 0 degree angle of attack, CL values are depending on the octant.
    In some cases, even the signs are different.
    On the other hand, for 2 degrees angle of attack, the dependence on the octant is small and  CL values are close to the experimental value.
    CL values at 0 degrees angle of attack are sufficiently small compared to CL values at 2 degrees angle of attack that they can be regarded as zero.
     
    By the way, regarding the boundary layer, I think it is essential to set up the boundary layer element in order to obtain highly accurate results.
    This is especially effective for problems where the viscous stress acting on the wall surface has a significant effect on the calculation results.
    For airfoil type problems, I recommend inserting about 10 layers of boundary layers.
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