surface integrated mass flux at inlet and outlet

Unknown

Hi all,

I was evaluating the surface integrated mass flux at the inlet and outlet of my model. 

In the inlet section, the values of surface integrated mass flux is negative:-

 

But, in the outlet section, its value is positive:-

 

From the thermodynamics point of view, mass transfer to the system is positive while mass transfer from the system to the surrounding is negative.

The same goes to the surface integrated heat flux.

Can someone explain why is this different in acusolve?

 

Thanks and regards,

 

acupro

The surface integrated mass flux (really mass flow rate) definition includes the u-dot-n term - so the velocity direction and the surface normal direction, where the surface normal is positive outward from the parent volume of that surface.  At the inlet, the velocity direction is opposite the surface normal direction, so the result is negative.  At the inlet, the velocity direction is the same as the surface normal direction, so the result is positive.

The integral definitions for the integrated surface outputs can be found toward the bottom of the acuTrans page in the Program Reference Manual:

https://help.altair.com/hwcfdsolvers/acusolve/topics/acusolve/post_processing_programs_acutrans.htm

acupro

The surface integrated mass flux (really mass flow rate) definition includes the u-dot-n term - so the velocity direction and the surface normal direction, where the surface normal is positive outward from the parent volume of that surface.  At the inlet, the velocity direction is opposite the surface normal direction, so the result is negative.  At the inlet, the velocity direction is the same as the surface normal direction, so the result is positive.

The integral definitions for the integrated surface outputs can be found toward the bottom of the acuTrans page in the Program Reference Manual:

https://help.altair.com/hwcfdsolvers/acusolve/topics/acusolve/post_processing_programs_acutrans.htm