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-   -   reverse flow in pressure outlet (https://www.cfd-online.com/Forums/fluent/94824-reverse-flow-pressure-outlet.html)

 Thomas Getza November 27, 2011 12:20

reverse flow in pressure outlet

Hi everyone, Im new using fluent and for my BS tesis I have to simulate boundary layer separation across a cylinder in cross-flow. I have reverse flow in the pressure outlet, and my tesis advisor told me I have to know how can the reverse flow affect my results. I have been looking in the tutorials and the manual, but cant find something about it.Hope you can help me (Im learning english too, sorry by gramar).

 ghost82 November 27, 2011 12:39

How far is your outlet from the cylinder?
Maybe that by increasing this distance reverse flow disappears..

 shk12345 November 27, 2011 12:48

Hello
I am also facing the same problem.The solution for this problem can be increasing the area of the outlet or by stretching the pressure outlet a bit far more or by decreasing the velocity at the inlet.
Hope that will help u .

SHK

 emreg November 27, 2011 13:45

hi..

pay attention to your boundary conditions.

is the velocity assigned in the correct way?

 prishor October 10, 2012 05:17

hi,

i am doing multiphase flow simulation in fluidized bed reactor..me also facing the problem of reversed flow in pressure outlet.. what can i do to eliminate this.

thanks and regards,

prishor p k

 nkme2007 October 10, 2012 05:40

Hello All,

I want to do analysis of heat transfer from water flowing through pipes submerged inside concrete. I am modelling in GAMBIT and wish to analyse it on Ansys FLUENT.

Can anybody help me out, how to model and simulate?

Does any tutorials exist?

 davidwilcox October 10, 2012 15:55

I have encountered on numeral times the problems of reversed flow. Normally, it has to do with the boundary condition you set at the outlet. Feel free to correct me, but i think that if you were to use the "pressure outlet" boundary condition at the outlet, your outlet must be set far away from the object of interest. In Fluent, I normally use the " outflow" boundary condition at the outlet and it does not give me reverse flow. :)

 misagh October 10, 2012 16:51

i had the same problem.i changed the urf(under relaxation factor) and the problem eliminated.
i am not sure whether it solves your problem or not...
best regards

 diamondx October 10, 2012 16:57

reverse flow means some element are entering instead of going out.
is your mesh structured or unstructured ??

 gera October 12, 2012 00:41

Hello All,

I often have a problem with reversed flow at pressure outlet.
I saw a lot of messages in this and other forums.

As I understand, the best way to overcome the reversed flow is to to set outlet far from a region where the main flow occurs.

On the other hand, I don't know what to do if you cannot change position of outlet. Does anybody know what to do in such case?

diamondx, is type of mesh (structured or unstructured) important?

davidwilcox, as far as I know outflow is not compatible with compressible flow problem. What to do in compressible flow problem?

 Bionico October 12, 2012 02:44

Hi gera,
in your case it is better choosing pressure outlet: anyway there may be some faces with reversed flow. In post processing you would see some streamlines going backward... it's occur when there are swirl and recirculation so don't worry :)

Regards

 msatrustegui October 26, 2012 05:44

Hi everyone,

I'm facing a similar problem. I'm simulating a centrifugal fan in fluent and the outlet is defined as pressure outlet.

The pressure-outlet get me to a result with reversed flow, so my professor recomended me to change the type of outlet to outlet-vent. With this change the reversed flow got eliminated. I also tried changing the outlet to a bigger one, but it didn't work. Is there another way to eliminate the reversed flow?

Thanks,
Marco.

reversed flow at the hydraulic centrifugal pump outlet

Hi !
I am an ansys fluent new user and I am working on my thesis! I am simulating the flow through a radial centrifugal pump but I am always having a reversed flow at the outlet ! I don't really know haow to deal with this problem! I ll appreciate any help ! Thank you

 karthikvv May 29, 2015 02:30

reverse flow in pressure outlet

It got resolved by reducing the velocity at inlet otherwise increase domain length after the region of interest
If you use boundary condition as outflow instead of pressure outlet it will stop reversed flow.

 tomss August 5, 2015 10:42

same problem

can somebody help me. I've the same problem. I've been try to change pressure outlet to outflow or reduce the URF. But the result always be the same

 nisarfatimaaeroengr@gmail May 18, 2016 16:35

reversed flow at pressure outlet and divergence encountered later.

Hi everyone,
I am currently involved in a unsteady aerodynamics project related to wind turbine flow physics. I have tried with different meshes (made using ICEM CFD unstructured)
but every time it gets into divergence after initial warning of reversed flow at outlet in fluent. The problem comes after three revolutions of rotor. I am not able to predict the real reason and the remedy.

More than 8 million elements are being used. Since the rotor blade profile is very complicated, the quality of mesh is not that gud. However, simulations are running fine for three revolutions with out getting into any problem or warnings.
Algorithm applied is LES model with SIMPLE technique and sliding mesh approach. Kindly help, if possible. :confused:

 venkateshaero May 27, 2016 04:11

Try to adjust time step size with 1deg rotation angle & Use CFX Solver

 nisarfatimaaeroengr@gmail May 27, 2016 13:48

Thanks for solution. However, I have already used time step size as 0.001 but still the case was going into divergence. To overcome this, I did reduction of urp to 0.2 and the case started working again. :)

 rajann_786 February 26, 2017 02:24

It happens due to a poor quality of mesh, abnormal boundary condition at inlet/outlet, short downstream length etc.
Remedies are:
> if vortex formation/recirculation of flow near an outlet boundary, increase the downstream length.
> check the mesh quality, improve it.
> use higher order scheme
> At last reduce the relaxation factor if necessary.

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