Hi

Iam new in fluent and right now I am using fluent 5.5 to stimulate a combustion problem, but when I run it it runs but giving me a message "reverse flow in 18 faces in outflow" and "turbulency viscosity limited to viscosity ration of 1.00e5 in cells" so what these message real means , is there any problem with my work if so how can I improve it..??

Please I need your help.. Kiraka

Hi Kiraka.

For how long have you tried to run the calc.? The calc. often (well, in my case anyway) start with reversed flow. Weather the solution should have reversed flow, depend on your problem. The size of the viscosity ratio is also problem dependent. Sometimes this ratio is restrained in the beginning of the calc. until the "correct" flowpattern is established. Have you scaled your model ?

Cheers Christian

I also have met such problems while using ASM modeling. Could you give me some advice? how to get rid of it? Thanks a lot!

I think at least three factors will result in what you met. 1) You haven't run your simulation long enough to build up a stable flow. Usually, this message only appears at the initial stage of your simulation. 2) The quality of your computational grids is not good enough. You should check your grids before you start your calculation. From my experience, use hex(3d) or quad(2d) elements if possible. 3) This is the nature of the flow pattern of your problem. I mean reverse flow. For example, in most situation, you can expect a reverse flow occuring at one of the outlets of a cyclone separator.

Thanx Christian and Jichun for the your advices which enlighten me a lot.

Coming back to my problem; I ran the calc. for about more than 2,000 iteration and the message is keeping coming after each iteration, I used hybrid meshing in 3D. So I will try Jichun apinion to see what will happen

Well, if you ran the case for 2000 extra iterations, what if in your problem some reverse flow is expected? Could you give more details about your case? As in cyclones, you can find reverse flow in internal cavities of gas turbines.

Cheers

Ok my case is that I am have an inner wall which is required to heat a fluid flowing outside it in order to support a reaction on fluid side. The fluid flow is affected by natural convection as well as bouyancy. The fluid flow is flowing upperward, and assumed the inner surface has a constant temperature ( but even though I ddn't manage to propagate the heat energy to fluid side, can anyone help on that too)

Kiraka

"natural convection as well as bouyancy"! What do you mean?

what I meant that there is heat energy flowing on natural convection as well as there is natural flow of fluid in the system....am I mixing things here..???

Kiraka

Sorry for mixing thinks up.....what I meant is that there is natural convection or boyancy effect in the flow

Kiraka

Natural convection, by definition, is driven by a body force such as gravity. Heat induces density gradients; and coupled with gravity field, this induces buoyancy. What I mean to say is that natural convection in your case has to have buoyancy! You seem to have separated the two in your statement.

You wrote faster. Sorry

[Shuveksha]

How can this reversed flow issue be solved? It shows in previous iteration and after that it dissapears. Has it been solved later or need to re run the simulation?