[a.morang]

Dear community,

I was trying to perform a simulation of an actuator disk and reviewing the source code C++ in "actuationDiskSourceTemplates.C" there is a line with the calculation of T (total thrust).

scalar T = 2.0*upRho*diskArea_*mag(upU)*a*(1 - a);

if mag() calculates the magnitude of a field, is there is a bug? because the thrust should be:

scalar T = 2.0*upRho*diskArea_*sqr(mag(upU))*a*(1 - a);

Probably I am considering something wrong because is not a new implementation and have been tested a lot but if anybody can help I will appreciate it very much.

Thanks and regards from Spain!
amg.

[mAlletto]

I think this is correct since mag calculates the magnitude and not the magnitude squared


see, e.g. http://foam.sourceforge.net/docs/Gui...mmersGuide.pdf

[a.morang]

Originally Posted by mAlletto

I think this is correct since mag calculates the magnitude and not the magnitude squared


see, e.g. http://foam.sourceforge.net/docs/Gui...mmersGuide.pdf

sqr is the squared:

sqr(mag(U)) == mag(U)*mag(U)

for it my question... In the original code U is not squared and should be because if not the units are not correct unless:

mag(U) = Ux^2 + Uy^2 + Uz^2

[mAlletto]

The units are correct since the complete calculation of the force is:



scalar T = 2.0*upRho*diskArea_*mag(upU)*a*(1 - a);
forAll(cells, i){Usource[cells[i]] += ((Vcells[cells[i]]/V())*T*E) & upU;}

[a.morang]

Originally Posted by mAlletto

The units are correct since the complete calculation of the force is:



scalar T = 2.0*upRho*diskArea_*mag(upU)*a*(1 - a);
forAll(cells, i){Usource[cells[i]] += ((Vcells[cells[i]]/V())*T*E) & upU;}

Do you mean that in C++:

upU & upU == upU^2

Thanks.
amg.

[mAlletto]

yes. The dot product of two vectors is equal to the magnitude squared:


u & u = ux*ux + uy*uy + uz*uz

[a.morang]

Originally Posted by malletto

yes. The dot product of two vectors is equal to the magnitude squared:


U & u = ux*ux + uy*uy + uz*uz

thanks you very much for your time!!
Regards!