[Bran]

Hello,

I am trying to write a named expression in Fluent that changes the cell zone volumetric heat source term (W/m^3) over time.

Through experiments I have obtained a polynomial equation: y = -0.2546x^2 + 674.23x + 81291 where y is the heat source (W/m^3) and x is time (secs).

I'm having issues turning this into a functional named expression on Fluent.

1: I tried typing -0.2546*t^2 + 674.23*t + 81291

When I try to incorporate this as a named expression, I obtain an error "Units mismatch"

2: -0.2546 [W/m^3] *t^2 + 674.23 [W/m^3] *t + 81291 [W/m^3]

Gives me a units mismatch warning

2: I tried -0.2546 [W*s^2/m^3] *t^2 + 674.23 [W*s/m^3] *t + 81291 [W/m^3]

But this also gives me an error that there is a unit mismatch

The logic of the source term is split into 4 sections:

Time of 0 to 100 seconds, source term should be 150,000 W/m3.
Time of 101 to 250 seconds the source term should be increased to 230,000 W/m3,
Time of 251 to 500 seconds the source term increases again to 350,000 W/m3,
Time of 501 to 750 seconds the source term 450,000 W/m3
Time of 751 to 1250 seconds the source term should be 525,00 W/m3

I played around and it may work out to this statement here:
IF(t<=100[s], 150000 [W/m^3], IF(101[s]<=t<=250[s], 230000 [W/m^3], IF(251[s]<=t<=500[s], 350000 [W/m^3], IF(501[s]<=t<=750[s], 450000 [W/m^3], IF(t>=751[s], 525000 [W/m^3], 0[W/m^3])))))

Would this be appropriate?

[AlexanderZ]

was

2: I tried -0.2546 [W*s^2/m^3] *t^2 + 674.23 [W*s/m^3] *t + 81291 [W/m^3]

try this

 -0.2546 [W/m^3/s^2] *t^2 + 674.23 [W/m^3/s] *t + 81291 [W/m^3]

also, you may use time dependent profile for heat source