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-   -   pressure distribution over an airfoil (https://www.cfd-online.com/Forums/openfoam-solving/102831-pressure-distribution-over-airfoil.html)

appa June 4, 2012 05:15
pressure distribution over an airfoil
 
Hello everybody,
I am trying ti simulate an airfoil using the solver simpleFoam. I want to have a pressure distribution as if the flux is real. The airfoil I'm using is a NASA/Langley GAW-1, it's used on the piper Tomahawk, the velocity is the cruise velocity =45m/s , and the ambiant pressure should be 797.952hPa at an altitude of 2000m. The file p at the 0 directory is modified in this way
Quote:
dimensions [0 2 -2 0 0 0 0];

internalField uniform 79795.2;

boundaryField
{
inlet
{

type fixedValue ;
value uniform 79495.2


}

outlet
{
type fixedValue ;
value uniform 79495.2
}

wall
{
type zeroGradient;
}

frontAndBack
{
type empty;
}
}
but when I simulate the case I get positif pressure over the upper surface of the airfoil which is impossible!!can someone help me please ?
can

kmooney June 4, 2012 10:57
It appears that you are imposing the same fixed value pressure boundary condition on the inlet and the outlet. Do you think it is a safe assumption that there is no pressure drop across the airfoil? This is a rather high Re flow so it might be more or less inviscid and you might be right (I'm not too familiar with aerodynamic flows).

Also, simpleFoam is an incompressible solver so the absolute value of pressure is somewhat meaningless, only the gradient participates in the flow equations.

appa June 4, 2012 14:06
Quote:
Originally Posted by kmooney (Post 364661)
It appears that you are imposing the same fixed value pressure boundary condition on the inlet and the outlet. Do you think it is a safe assumption that there is no pressure drop across the airfoil? This is a rather high Re flow so it might be more or less inviscid and you might be right (I'm not too familiar with aerodynamic flows).

Also, simpleFoam is an incompressible solver so the absolute value of pressure is somewhat meaningless, only the gradient participates in the flow equations.
As far as I know, there shouldn't be a pressure drop. And you're right about the gradient thing but I want to get finally real values of pressure, I don't know how can I introduce this information ?

sail June 4, 2012 14:43
what you are defining in the p file is the dynamic pressure, while you are using the values for the static pressure.

if you want to see the actual pressure numbers on your plot, just perform the simulation with the right bc for pressure and add your static pressure value during the postprocessing in paraview using the calculator.

appa June 4, 2012 19:00
1 Attachment(s)
Quote:
Originally Posted by sail (Post 364697)
what you are defining in the p file is the dynamic pressure, while you are using the values for the static pressure.

if you want to see the actual pressure numbers on your plot, just perform the simulation with the right bc for pressure and add your static pressure value during the postprocessing in paraview using the calculator.
could you please give me more details, I modified the boundary conditions and attached a picture of what I did using the calculator, but I still don't have the ambiant pressure at least in the inlet and outlet

buaawangwei March 21, 2014 07:46
Dear appa,
I am a student,now I want to find the accurate coordinates of GAW-1.
Thank you very much.


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