Hello i'm working with CFX in a model of a solar chimney and i'm trying to run a transient problem where the inlet temperature changes with time! i have seen that the velocity in the chimney depends on the reference temperature of the Boussinesq model that i'm using! my question what reference temperature should i use?

David,

The Buossinesq model is valid when the temperature range is around 10 degrees or less as it is still a constant density model. Beyond that (>10 deg) you should be using a compressible model. That said:

Try setting your reference temperature to the mean of your expected temperatures. This will allow gases colder than the mean to settle, while higher than the mean will rise. In a closed system, Tref shouldn't change your final solution (although higher buoyancy forces can cause stability issues). In an open system, Tref can be the ambient temperature, but you need to be careful not to induce false flows with very large body forces.

Jeff

Thank You! I used the ambient temperature for Tref! And it seems well!!!

David