Hello,

I want to model heat transfer (buyoancy-induced flow, diffusion) in a vertical cylinder with a high aspect ratio (L>>r). First I choose a 2D configuration (X-Y). The boundary conditions are : X = r et X = -r (lateral edges): wall conditions, non heat flux (insulated) Y = 0 (bottom): wall condition, fixed temperatute at 55°C Y = L (top): wall condition, fixed temperature at 15°C The interior is filled with water, I use the boussinesq approximation for density calculation. Gravitationnal acceleration is set 0 in x direction and -9.81 in Y direction. I do a steady simulation. Initial conditions are a 0 gauge pressure and a 35 °C temperature in all the domain. When I run the model, it is solving the energy equation but seems not to solve the flow equation, or not to take into account the gravity. Indeed, when I view the results, the static pressure remain 0 in the model (absolute pressure equal operating pressure), density is not modified too, only a temperature gradient is calculated by thermal diffusion. I wonder why I have not any hydrostatic pressure gradient in Y direction, and how can be the density uniform whereas there is a temperature gradient, the results make me think that gravitationnal acceleration is not working.Thanks for your help.

Virginie

Gravity is not turned on as disregarding any thermal density fluctuation modeling you should still get a hydrostatic pressure distribution. Fix that and your other problems will likely be solved.

I think there maybe two reasons: 1. you didnot set the thermal expansion coefficient in "material" panel; 2. The property values you set resulted in a very low Ra(Rayleigh number). if Ra is very low, the buoyancy-drived flow will not take place. the heat tranfer is thermal conduction, not convective heat transfer. for details, you can see the fluent help.