Define fluid domain for a given geometry.
 

Hello everyone,
My question is : how can the domain dimensions of a flow around an object be determined (in terms of dimensions and shape) ?



The flow depends on the effects that the object has on it. But does a general rule exists? Does the domain shape must look like to the one of the object in the flow ?


Here are some examples to illustrate my questions:
The flow around a flat plate: the transversal dimension can be 10 times the width of the boundary layer
The flow around a 2D NACA profile can have the form of a U inclined (C-grid mesh for example) with dimension of 20 times chord length for the diameter of the U domain
- If it is a 3D NACA profile, we take the same U in 3D and can enlarge the domain past the flow if we don’t know the effects of the flow on the object.
For the flow around a cylinder (2D case), if we choose a rectangular domain, it can be 20 times the diameter on the width, 20 times the diameter past the cylinder and 10 times for the inlet domain.



WWhat is the methodology to adopt in general ?
Thank you very much for your advices.
Thomas