modelling of buoyancy-driven flow

khaiching

Dear colleagues:

I have a couple of questions arisen when I am modelling some buoyancy-driven flows for indoor airflow application. Hope that you all can share your ideas with me..

(1) It is well-known that the addition of buoyancy source terms in the momentum equation (say z-momentum) will induce numerical instability in the solution process. To resolve that, one might probably reduce the linear/inertial relaxation factor to obtain the steady-state solution. In many cases that I have tested (I would say all), these methods DO NOT work at all to me....I have to solve the transient equations(using transient SIMPLE) to time-march the solution to steady-state to ensure numerical stability, which may be time-comsuming if steady-state solution is desired. My question is: Is that really no way for me to solve the steady-state governing equations, while ensuring that the stability is not severely diminished?? Pls advise..

(2) Regarding the implementation of Boussinesq buoyancy model, which is adopted if dT (difference in Temperature) is low in a flow situation, what will be the correct value of T0 (i.e. the reference temperature)?? How to define T0?? Many of the paper suggest T0 as the bulk temperature; BTW, what is the definition of bulk temperature??

Any thoughts will be helpful. Thanks in advance..

-khai ching-