[adambarfi]

hi everybody

I'm analyzing a stack that is axisymmetric with boussinesq. my Rayleigh number is 1e9 and convergence didn't obtain. the results are wrong. when I changed the gravity acceleration to 0.098 that corresponding Rayleigh is 1e7 the solution converged. how can I reach to convergence with Rayleigh above 1e7??
please help me

thank you

[meangreen]

Can you post more details about the problem? Please define the Raleigh number.

[adambarfi]

Originally Posted by meangreen

Can you post more details about the problem? Please define the Raleigh number.

thank you meangreen,
assume you have a stack that it's geometry is axisymmetric. the air with T=405K and V=0.08m/s enters and the stack is in the surroundings with ambient T and P. my outlet boundary condition is pressure-outlet. a picture of model is attached.

Rayleigh number is a measure of laminar or turbulence. if it was greater than 10^7 the viscous model is turbulent and if it was below 10^7, it is laminar:
Ra=(g*beta*(T2-T1)*L^3*rho)/(mu*alpha)

I overcome this problem by changing the Specification Method to Intensity and Hydraulic Diameter and Turb. Intensity=7% and Hydraulic Diameter=150mm at inlet and outlets.

the solution converged but the results seems to be wrong. I can't understand where I make mistake that this results obtained.

[adambarfi]

Isn't here anybody can help me!!!!!! Please.