[openFUser]

Dear Foamers,

I am quite new to use OF to solve external aerodynamics. I am writing here to ask for your kind help.
I try to simulate a cube placed on the ground on a face in order to understand how OF manage the force calculation with simpleFoam and with buoyantSimpleFoam.
The point is that I should get the same value of forces on the cube, but something is wrong...
I tried to compare the data in the postProcessing/forces folder with the value obtained by the integral of pressure on the cube's surfaces in paraFoam but i cant get the point.
Maybe I make some mistakes: to integrate pressure on faces I generate surface normals on the cube and the integrate the calculated variable p*normals.

The topics are these:
1. there is any differences on forceCalculation between simple and buoyant?
2. why the intergals of (p*normals) do not match with the force calculation of postProcessing folder?

I'd like to thank anyone could help me...


Here below there some values:


/*___with simpleFoam___*/

P
pressure 0;
dimensions [0 2 -2 0 0 0 0];

--> after 50k iter

forces(pressure, viscous, porous)
(-1.677823966 -0.04192667675 0.8973219913) only pressure

while with the integrateVariable on P
1.47393 -0.0309424 -0.895828


/*___withbuoyantSimpleFoam____*/

P
pressure 101325;
dimensions [1 -1 -2 0 0 0 0];

P_RGH
pressure 100000;
dimensions [1 -1 -2 0 0 0 0];

--> after 50k iter
forces(pressure, viscous, porous)
(-3.544135454 -0.2622319888 -24650.00027) only pressure

while with the integrateVariable on P_rgh
193.717 421.979 26073.8


while with the integrateVariable on P
193.71 421.967 26072.3

[nimasam]

look the dimensions of pressure in both solvers , if you look carefully you will find out simpleFoam uses pressure/rho as p

[openFUser]

first of all, thanks for your reply.
I know that simpleFoam solve P/rho. The point is: why I obtain two different results with the two solvers for the same problem?

moreover i don't understand why when I compare the Force pressure data in the postProcess folder with the integral of pressure done in paraFoam I can't get the same values.

thanks

[nimasam]

about why this solvers return different results, as i said it returns to definition of pressure , may be if you want multiply result from simpleFoam in rho, you find much similar result with bouyantSimpleFoam

and about the second question, it returns how you calculate your values in paraView

[Sherlock_1812]

Hi Nima,

I would also like to know how results from buoyantBoussinesqSimpleFoam would compare with results from simpleFoam with buoyancy source term added to UEqn (similarly their unsteady counterparts). For similar settings, I can see that pressure is treated differently. For simpleFoam pressure is p/rho for incompressible case

What changes should one make (in SimpleFoam) to get similar results in both?