Scalar problem

Dougal McQueen

{CFX-4} I am advecting a scalar quantity into the domain (potential temperature = 293) by setting the inlet boundary condition with usrbcs. The trouble is the scalar disappears downwind (not a transient run). The inlet condition is correct, but quickly downwind the scalar quantity disappears to zero. I have the diffusivity set to 2.7e-05 (which taken from physical charts). Anybody know any reason for this.

Also, I want to know whether my wall boundary condition for the ground is set right using usrbcs. I have set A=1, B=0, and C=ground temperature.

Many thanks in advance

Dougal