Vortex in a pipe / Solutions or approximations? I want to study a vortex flow in a pipe; in other words helical flow.
A couple introductory texts on fluid mechanics (e.g. Shames, Mechanics of Fluids) describe the solution to vortex flow in 2D:
$$V_{\theta} = \frac \Gamma {(2 \pi r)}$$
(with a singularity at the center).  However, what about a vortex in a pipe?

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*If I assume irrotational flow down a pipe, can I establish a helical vortex (e.g. $V_r = 0$; $V_z > 0$; $V_\theta> 0$)?

*Is it merely superposition (e.g. irrotational 2D + parabolic laminar or irrotational 2D + plug flow)?

Is there a reference you can suggest to read about this phenomena?
If this is solved using CFD, then how do I identify which types of CFD are appropriate?  Is this still merely a potential flow?  What is the simplest CFD that would solve this type of problem?
 A: This depending on the velocity and dimensions is a most probably turbulent flow which can be solved by finite volume and a simple turbulence model such as k-omega or k-epsilon.
I do not know what you mena by which type of CFD should I use. You can use a pre-existing library or a commercial solver such as ANSYS Fluent.
The geometry of the pipe is not known, but if it is an elbow there would be cavity flow as well. However, the equations are all the same (Navier-Stokes) and the best and easiest numerical scheme is finite volume.
These are 2 references explaining this phenomenon to some extent:

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*J. B. Nuttall, "Axial Flow in a Vortex", Nature 172, 582–583 (1953).


*A. Bottaro, I. L. Ryhming, M. B. Wehrli, F. S. Rys, P. Rys, "Laminar swirling flow and vortex breakdown in a pipe", Comput. Methods in Appl. Mech. Eng. 89 (1991) 41-57.
A: It is fully non-sense to treat potantial flow as non-viscous. In fluid, theare only two flows are non-viscous. First flow is a constant velocity (m/s) one. Second one is quasi-rigid rotation (in vortex core) with constant angular (radian/s) velocity. People of even age of 80 y.o. make errors treating irrotational flows as non-viscous ones and rotational flows as viscouse (second type flow is rotational but non-viscous). 
For discussion, write to Pavlo_Lukianov@nau.edu.ua      
