reversed flow at pressure inlet and turbulent viscosity is limited....
 

Hello All :)

I am quite new to the forum & FLUENT and try to present my problem setup here:

My Mesh has 4.9 million hexa cells

Fluent----3d --- parallel---k-epsilon model--- residuals 10^-4

I am simulating a cylindrical domain( Symmetry:BC) where another cylindircal domain starts almost closely to the pressure inlet, at the opening of the outer cylinder.

problem: In the Fluent cortex I receive the message :

turbulent viscosity limited to viscosity ratio of 1.000000e+05 in 285 cells
and
reversed flow in 3380 faces on pressure-inlet 101

My URF of Turb. Viscosity is set to 1 and
i tried to balance by setting URF sum of Pressure and velocity as 1 (for example like 0.1-0.9 0.2- 0.8 )

I used the Turbulence specification method as Intensity and Hydraulic Diameter

I calculated the intensity of entering air at presuure inlet using a velocity of 1 m/s.

I get both reversed flow and turbulent viscosity warning repeatedly but. solution converges atleast first 100 iterations

Questions:
1.does setting turbulent viscosity ratio by FLUENT affect my Results ?
2. how to find the exact turbulent intensity at pressure inlet ( I dont have readily the air velocity,i should take it randomly... how to set this air velocity)?:confused:

More inputs and suggestions are greatly appriciated.....i have little time to get around this....please help

thanks a lot :)

This is typical initialization issues (reverse flow & turbulence).
I assume your are working with pressure difference between inlet and outlet. For the pressure initialization, try to set it in order with 1/2 of your pressure loss. (it should correct your reversed flow issue, if not, try to enforce the flow direction with the initialization of velocity computed from velocity inlet, see bottom)
You may have also an idea of the massflow which should be generated through this pressure loss (empiric equation, etc...).
It gives an idea of your the velocity inlet. From here you can set the turbulence quantities at your inlet (Even if your massfow assumption isn't 100% exact, your initialization will be more accurate)
Hope it helps

Firstly thank u max :)

Yeah! you are right...after trying hard....i set my inflow BC as "velocity inlet" and NOT as Pressure Inlet

At velocity inlet I assigned the exact values of Turb. Intensity and hydraulic diameter of the inlet.....Then it initialized the flow well with out any reversed flow and rest iterations went well......

I think in case of reversed flow at inlets its better to switch "velocity inlets" , if one has the exact values there....

nice day
:)

You could let the pressure Inlet as prior, but set the turbulent BC as you did for the velocity inlet BC