[ClaraP]

I am a beginner in using Ansys CFX and also a beginner in engineering field.
I have the modelisation of a chamber and for the moment the fluid which will go through it will be water. I need a laminar flow inside the chamber but I don't know its behaviour inside the chamber, so I don't know if I have to put "Laminar flow" or another thing.

[ghorrocks]

This is not a CFD question. It is a basic fluid mechanics question. Work out the Reynolds Number of the flow in the device and look to see if that Reynolds Number indicates turbulence or not. That will give you a good starting point as to whether it is turbulent of not.

[ClaraP]

Thanks, but how do I calculate the Reynolds number with the geometry I have ? It's an "elliptic" tube (made with 3 circular tubes of 1mm of diameter) and a circular chamber.

[evcelica]

Re = (Density * Velocity * LengthScale) / Viscosity
For internal flows LengthScale is usually the hydraulic diameter = 4*Area/Perimeter.

Like Glenn says, this is absolutely basic fluids stuff, that shouldn't be asked on a CFD forum. Just google Reynolds number, or read through any fluid mechanics text.

[ClaraP]

First, I know the formula of Reynolds number, thanks, it's just that I don't have a simple circular tube, the geometry changes and I don't know the velocity of the fluid ! Then, my initial question was was about the software, because I don't know how to calculate the Reynolds number in my case, and I thought there was an option that can deal with both laminar and turbulent, I don't know !

[ghorrocks]

You don't need an exact calculation. Just estimate the velocity scale based on your best estimate. It is just a guide as to whether it is turbulent or not, and the transition point is defined over a range of about a power of ten anyway, so precision is not required.

Once you know the simulation is laminar or turbulent you then select the simulation options to suit this. Performing a model where the simulation works out whether it is turbulent or not itself are far more difficult.