[Henriqueg]

Hi, everyone.

I have to simulate a case of external natural convection. In order to know better the process using CFX, i´m simulating natural convection over a heated vertical infinite plate, with constant temperature. I have used simmetry condition to the side surfaces, and opening condition (static pressure - entrain) to the upper and downer surfaces, and to the surface that is opposite to the plate far away from the plate). I´ve used this far away distance six times the height of the domain. I´m using steady flow approach. Initially, i´ve set up the gravity to -9,8 m/s^2 in the "y" direction, and the flow was considered turbulent. In order to guarantee the flow is laminar, i´ve changed the gravity to -0.098 (i saw this in fluent user´s guide). The rayleigh number was close to 10^7. But, in some cases, depending on the time scale i-ve used the fluid velocity found in the solver was told zero and there was no rayleigh or reynolds number. In other cases, with different time scales, cfx found rayleigh number close to 10^7 (laminar flow) but reynolds number that corresponded to a turbulente flow (10^4). What is going on here?

Thanks,
Henrique.