[ibadullah safdar]

Dear all,
I need assistance in CFX. Below is the message that occurs in solver manager during iterations. So should i have to continue my iteration till convergence or i have to cater that notice. The solver manager still running with this message so should i have to wait till its convergence as i am upgrading my iterations during its running. Please help i am very thankful if someone sort me out from this.

A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 31.8% of the faces, 17.3% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: output 1. |
| The fluid name is: water. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead.

[ghorrocks]

FAQ: http://www.cfd-online.com/Wiki/Ansys...f_an_OUTLET.22

[ibadullah safdar]

Thanks ghorocks it is informative. Actually that message disappears after increasing my time scale but the result is still not converging as solver has done iterations up to 675. some of the equations results were repeated in most of the iterations but unable to produce the produce the consecutive same results so that the convergence will occur. so what did u suggest should i have to wait until its convergence or what i have to do. plz suggest. the pic of graph is shown in attached file.

[-Maxim-]

sometimes starting with a larger time step helps to 'flush' the domains and establish the right flow direction. You should also watch the imbalances during the run.
Later (according to your screenshot: now) you could use a smaller time step which might help your simulation to converge further.
But I think this is already explained in the FAQ and the wiki here.

[ghorrocks]

That's right maxim, Ibadullah's question is a different FAQ now: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

[ibadullah safdar]

Thanks maxima for ur reply. I did what u said but no convergence takes place as it becomes smooth for a short time but after some iterations the same message starts occurring so I have decided to change my outlet condition from average static pressure to simply a static pressure. I hope it will work as this is the most robust option i learned in CFX pre guide.

[ibadullah safdar]

Dear all,
I am facing that error problem shown below. The figure of geometry is also shown below. By viewing fig i dont think so that flow seperation can occur at the outlet but the problem persist. In fig the water is injected from small nozzle situated on throat area and air is injected from input of big nozzle from left side.
Notice ****** |
A wall has been placed at portion(s) of an OUTLET |
| boundary condition (at 31.8% of the faces, 17.3% of the area) |
| to prevent fluid from flowing into the domain. |
| The boundary condition name is: output 1. |
| The fluid name is: water. |
| If this situation persists, consider switching |
| to an Opening type boundary condition instead
+--------------------------------------------------------------------+
i have tried many options such as
1. changing the outlet boundary condition from average static pressure to simply static pressure.
2. then changing the outlet boundary condition to mass flow rate that i am using in the domain (total mass flow rate of air plus the water).
3. by controlling the timescale factor in above two options but convergence did not occur and the same message will occur after some iterations.
So should i have to amends in my geometry by increasing the diverging angle from 3.8 to 5 or some better option can any one tell me.
I shall be very thankful if someone sort me out from this problem.

[ghorrocks]

Your geometry is liable to have a large separation in it (in the diffuser section), so it is no surprise you are getting the warning about reverse flow at the outlet.

In this case forget about fiddling with solver settings and move the outlet boundary downstream far enough that the flow has got past any recirculations. Note this can be quite a distance in some cases.

[ibadullah safdar]

thanks ghorocks for ur reply.
There is one query in my mind that my diffuser angle in this case is 3.8 whereas i read in one of the link that the diffuser angle should be between 5 to 8. So I think i should increase the diffuser angle instead of increasing the length of the diverging section or moving downstream the outlet section. What do you suggest
https://www.quora.com/Why-is-the-len...the-converging

[ghorrocks]

First of all: do not PM with duplicates of messages you post on the forum. I find that very annoying. If it is on the forum I will see it.

You can do whatever you like, only you know the purpose of why you are doing this model so only you can say what is an appropriate way forwards. Which ever approach you decide to use, you will find convergence much easier if you arrange it so the flow is all in the forwards direction at the outlet with no recirculations. You can do that by changing the diffuser angle, adding a straight section of pipe at the end, discharging into a large box, or many other method. Whatever straightens the flow out.

[ibadullah safdar]

Thanks for ur reply and sorry for the private message as i dont know that you dont like pm because I am new in this forum. Once again I am sorry for that.