[Ritah]

Hello,

I am doing a near-wall modelling in a 2D channel flow. So I have a fluid (liquid Zn) with a small fraction of Al-liquid (0.2%) entering the channel (10 cm wide, 1 m long) at 1m/s. I use Energy and Viscous model (k-Omega or k-Epsilon), and for Al I use a UDS Transport Approach instead of Species Transport. A heat flux and a mass flux for Al are applied on the lower wall of the channel. So I have defined a UDS , which has a value of 0.002 at inlet, and a molar flux of -0.001 at the lower wall. For mesh, I use different meshes for various y+ values (from1 to 50).

After calculation in Fluent I obtain the normal boundary layer solution for Velocity and temperature, showing a Gradient behaviour, but for Al-concentration I don't get any boundary layer as though there is no UDS equation solved. Please see the attached Pictures.

If you have an idea what could be the cause of this behavior (no boundary layer for Al species), please let me know.

Thank you ,

Andreea

[AlexanderZ]

you may clearly check if UDS equation is solving or not in fluent console,
also you can go to Solution controls -> equations and check there

[vinerm]

Hi

By default, UDS equation is laminar, i.e., the effect of turbulence is not included in diffusion component. You have to include the effect of turbulence by adding ratio of turbulence viscosity and Schmidt number to UDS diffusion coefficient.

Vinerm

[Ritah]

Hi ,

Thank you for your answers.

yes, it turns out turbulence plays a dominant role, since the diffusivity of liquid Al/zn is very small (9e-10). So, after taking turbulent diffusivity into account, the concentration boundary layer appeared as expected.

Thank you again for taking your time,

Andreea