Learning Forum

[chuminhkhue]

I am trying to solve the transport equation for a user-defined scalar (UDS) representing the number of particles in a single-phase flow, with velocity at the inlet and zero pressure at the outlet. The flux function I am using is the mass flow rate.

At the inlet, the particles are released at a rate specified as the number of particles per unit area per unit time (flux). The inlet concentration of RP is 2.5 × 10^14 particles/m³ and the inlet concentration of AP is 1.25 × 10^13 particles/m³.

I am defining the specific flux at the inlet as:

-1 × UDS diffusivity × grad(UDS) ⋅ n

with units of kg/(m⋅s) × particles/m³ × m⁻¹.

i conduct it by ufd profile like this

When I apply this specific flux model, my simulation crashes. However, when I set a specific value of 2.5 × 10^14 for RP and 1.25 × 10^13 for AP at the inlet, it runs but I am unsure if it is working correctly.

Can you help me understand why the specific flux model causes the crash and whether I am correctly setting up the boundary conditions for the UDS?

[Rob]

If you're using scalar gradients have you told Fluent to retain all values? Can't remember the exact term off hand, but there's a TUI command to avoid some gradients etc being discarded following their use in the calculations. It'll be covered in the Scalar bit of the manual if it's necessary. 

[thamilmani]

/solve/set/expert no no yes no

[chuminhkhue]

Thanks for your reply