Simcenter STAR-CCM+ Why does my Region Total Heat Source give lower Power when using an insidePart field function?

When you prescribe an insidePart field function e.g. insidePart(@GeometryPart("Block_2"))?1000:0 for the Region Heat Source in W this does not give 1000 W distributed across the Block_2 section.  

What you get is the equivalent to 1000W across the Region on the cells within Block_2 and 0W in the cells outside Block_2.  In this example the volume is 1/8 of the total volume and is equivalent to 125W.

A simple demo file (v2402) is attached to demonstrate the difference when setting the inside part function.

For simplicity the geometry is a 1m2 block which with 1000W Region Heat Source that will increase 1K every 1s.

After 10s you see that all the Region has risen to 310K. 

Now if the switch is made to the field function using an insidePart filter, it can be mistakenly assumed that the 1000W is applied solely within the Block_2 cells.  However, what this is now doing is applying the equivalent to 1000W in the cells inside Block_2 and turning off the Heat Source in the cell outside.

The equivalent scene to the one above shows mesh cells within Block_2 have reached 310K, but the other are still at 300K.  Therefore as the Block_2 is 1/8 of the size of the Region only 125W is being applied.

Hopefully this article has given a better understanding of how the Heat Source is being applied when using an insidePart function.