Mismatch of the drag with the summation of pressure and viscous drag
 

Hello, everyone,

I was simulating a 2D laminar flow around a square cylinder at Re = 100. The mean drag coefficient was around 1.45, which seemed ok. However, when I tried to calculate the pressure drag coefficient (by using custom field function of 'pressure coefficient * x face area' ) and viscous drag coefficient (by using custom field function of 'skin friction coefficient * x face area' ) separately, their summation was not exactly the same as the drag coefficient calculated directly from the software.

I am quite confused about this, could anyone tell me why this inconsistency occurs?

Thanks