Hello, could anybody suggest something for such situation.

There is a semi-transparent recirculating buoyant fluid flow (with optical length >> 1) in a cyllindrical tank and I need to include DT surface to surface radiation through ambient nonbuoyant air from other solid surfaces around. Fluid is in a solid tank, but top of the fluid has a common interface with the air.

Until now I am not able to define two different fluids with a common boundary as well as to neglect buoyancy in one of them. What would be options to solve this issue?

thanks for any advice

concerning my question - I found possibility to disable constant domain physics so two fluids (liquid in a tank with open surface and ambient air) can be defined - still weather both buoyant or both nonbuoyant, unfortunately. Although invention of two domains of variable composition mixture due to fluid/air interface existing in my geometry does not seem a good choice because steady and flat interface would be appreciated without additional numerical costs and no mixing of these regions. Solid nonbuoyant air with radiation heat transfer would be the best, but it is not possible because DT surface to surface radiation can be activated only in a fluid domain.

Any suggestions how to implement radiation heat transfer in two fluids having steady flat interface one buoyant, another nonbuoyant without defining a variable composition mixture consisting of liquid/air?