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abm October 8, 2008 07:00

Velocity inlet boundary conditions
Hello I am analysing the flow over an airfoil. But when I'm setting up the problem, this message appears: "WARNING: Velocity inlet boundary conditions are not appropriate for compressible flow problems. Please change the boundary condition types used for this problem" Then I can go on with the analysis, but I don't know what this problem means.

Thank you very much

doki October 8, 2008 07:21

Re: Velocity inlet boundary conditions
velocity inlet BC type, should only be used for incompressible flows. if your case is compressible, change it to pressure inlet or ...

abm October 8, 2008 07:49

Re: Velocity inlet boundary conditions
But if I change it to pressure inlet, how can I simulate a 30m/s flow over the airfoil?? Thank you

Rok Sibanc October 8, 2008 07:56

Re: Velocity inlet boundary conditions
Set inlet as mass flow inlet and calculate it as: area * velocity * density

DANG Huixue October 8, 2008 09:17

Re: Velocity inlet boundary conditions
you can define the total pressure as: 0.5 * rho * velocity * velocity, just the same as the dynamic pressure

CL October 8, 2008 10:37

Re: Velocity inlet boundary conditions
Hi abm, Dont use mass flow inlet as ur boundary condition becuase for compressible flow density is not constant, so mass flow will not be constant for compressible flows.

With regards, CL

kartik October 8, 2008 19:33

Re: Velocity inlet boundary conditions
Hey You could use Pressure Far field. you can specify the mac number for the velocity you want to provide.

abm October 9, 2008 03:35

Re: Velocity inlet boundary conditions
Thanks to all. Now I have to try all your suggestions, and I'll post the results here. But I think that using mass flow isn't a good idea, as CL said before

Thank you very much

doki October 9, 2008 03:59

Re: Velocity inlet boundary conditions
mass flow inlet is of course one of BCs for the compressible flow, but in the case, I think using pressure inlet is more appropriate. pressure far field is something used only for external flow problems, and needs the outer boundaries of the domain to be very far from the inner boundaries. and also it is recommended for M>=0.6 in such cases. by the way, the pressure inlet appears to be more suitable for the case.

abm October 25, 2008 08:51

Re: Velocity inlet boundary conditions
I'm analysing flow around an airfoil near the ground, so I think I can't use pressure far field, and as it's about compressible flow, for me mass inlet is not a good idea. What do you think?

doki October 26, 2008 07:25

Re: Velocity inlet boundary conditions
for the condition, I think you have better use Pressure inlet/outlet conditions. It is a tough problem to encounter, i Know. But sometimes there is no other choices.

abm October 26, 2008 11:11

Re: Velocity inlet boundary conditions
What I don't understand is that, even with this warning, nothing wrong seems to happen, and the results are ok.

doki October 27, 2008 12:39

Re: Velocity inlet boundary conditions
well, yes. there are so many conditions which have the same problem. In many cases there are such conditions in which there is no errors. but when you are doing sth right, then the errors appear!

abm October 29, 2008 05:03

Re: Velocity inlet boundary conditions
The problem happens when I change material density from constant to ideal-gas. I'm trying to prove that the results are ok, instead of this warning

hhh August 3, 2012 05:51

velocity inlet in fluent
Dear friends,
In fluent, For analysis of 2D naca0012 airfoil velocity inlet we give vcostheta in x component & vsintheta in y component, v is inlet velocity.

1)here i start analysis of 3D wing, for that i take naca 0012 airfoil & extrude 100mm, in gambit and analysis in fluent i have doubt how to set velocity inlet, here i consider my velocity is 50m/s, then what is xyz component,please let me know.

2)if you consider 3D wing, (vtantheta for z component) is correct or wrong, please let me know.

2) how to find angle of attack for 3D wing? please let me know

wingboys4 July 6, 2014 05:03

Fluent physics Setup
We have created the mesh for B-737 wing using ICEM CFD. We have not been able to do the physics setup for fluent.
We want to use the following conditions:
Mach Number :0.3
We have tried using velocity inlet for inlet conditions, pressure outlet for outlet and pressure farfield for top and bottom surfaces.
We have tried to use SST K-omega model but there were divergence detected.


mich_K October 18, 2014 08:52

If you specify pressure inlet as a BC, how do you attain a specified inlet velocity/Mach nr?

Also, when simulating flow over an airliner, would gauge total pressure be the ambient pressure at which the plane is flying, and what then would Supersonic/Initial gauge pressure be?

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