Hi, I am Munzir Mechanical Eng. I have practical case of flow in annulus, I'd like to simulate and study it in details with fluent,

my problem is the annulus i have is 3 meter in length and the flow enter and exit in vertical direction i am most interested in the effect of the entrance and exit as well as the horizontal flow along the annulus.

My current inquiry about the geometry, how can I make it shall I involve all the 3 meter in my simulation or what exactly.

My case will involve flow and heat transfer for laminar and turbulent regime for both Newtonian and non-Newtonian fluid.

Hello Munzir,

I've some experience of simulating flow in annulus and i think that there is no harm in taking three meter length of annulus but your geometry should be axisymmetric.

Regards, Muhammad Sohail, Junior Researcher, NEDUET, Karachi, Pakistan.

Hi Munzir,

I worked with this case in the early past and I suggest a very good reference that I used:

ESCUDIER, M. P.; GOULDSON, I. W.; OLIVEIRA, P. J.; PINHO, F. T. Effects of inner cylinder rotation on laminar flow of a Newtonian fluid through an eccentricity annulus, International Journal of Heat and Fluid Flow 21, p. 92 â€" 103, 2000.

ESCUDIER, M. P.; OLIVEIRA, P. J.; PINHO, F. T. Fully developed laminar flow of purely viscous non-Newtonian liquids though annuli, including effects of eccentricity and inner-cylinder rotation, International Journal of Heat and Fluid Flow 23, p. 52 â€" 73, 2002.

ESCUDIER, M. P.; OLIVEIRA, P. J.; PINHO, F. T.; SIMTH, S. Fully developed laminar flow of non-Newtonian liquids though annuli: comparison of numerical calculations with experiments, Experiments in Fluids 33, p. 101 â€" 111, 2002.

I can also remark some points that I think is relevant:

1. Length Entrance: I think that is relevant in your case because of yours regime range (laminar to turbulent). I recommend the paper, CHEBBI, R. Laminar flow of power-law fluids in the entrance region of a pipe, Chemical Engineering Science, 57, p. 4435 â€" 4443, 2002.

2. Flow regime: You can simulate turbulent Newtonian flow very well in Fluent (in the range of details that you can "computationally" afford). But for non-Newtonian fluids, this should be a difficult task, mainly because there is few models for this feature available. I know that Fluent have a "beta model", but you have to use as expert parameters (and I don't know how to configure this feature). Other aspect is the regime transition, I am not sure if the Florian SST model was already available for Fluent. In my opinion is the best transition model available in commercial CFD codes... (I am quite sure that is implemented in CFX).

And be careful with the transition criteria… this is a very trick subject for annular flow. I suggest: DESOUKY, S. E. D. M.; AWAD, M. N. A. A new laminar to turbulent transition criterion for yield-pseudoplastic fluids, Journal of Petroleum Science and Engineering, 19, p. 171 â€"176, 1998.

Other aspect is the mesh refinement near the walls, be assure that yours y+ is in the recommended range of your turbulence model.

3. The vertical inlet and outlet are perpendicular to the annular flow ? Because if you plan to rotate the internal cylinder (tube) you are going to masquerade the real tangential velocity profiles caused by the shaft rotation (axial inlet/outlet is a good option).

4. Concentric allows an axis-symmetry layout but eccentrics geometries will cost a little bit more computational effort, and be very careful with the "cells" orientation in eccentric arranges (divide the geometry in quadrants to build it).

I hope that my contributions could help you.

Regards

Ressel, Rio de Janeiro, Brazil