CFD Online Discussion Forums - Non-parabolic profile for fully-developed flow

I am using Fluent to investigate biomedical flows in coronary arteries and comparing computational results with experimental measurements.

I am experiencing some difficulties in obtaining comparable velocity contours from Fluent. I have used an in-house code to solve for the same geometry and flow conditions and it produced a much better agreement with my experiment. However, it is desirable to continue using Fluent as there is more functionality and ease of use.

I am concerned that for the straight tube inlet length that I have, Fluent gives me a blunt-paraboloid type velocity profile across the tube section about 15 diameters downstream of a velocity inlet when I would expect an exact parabolic profile for fully-developed flow. I think this would affect the velocity profiles of sections further downstream. Also, there is a significant diffusion effect as the velocities are significantly reduced in magnitude even when looking at the straight tube section.

The mesh used was using a spacing of 0.2 with 4 layers of prismatic elements with a growth rate of 1.2 and a first layer thickness of 0.05. I have a total of about 1.3 million elements in the geometry. I guess that I could flood the geometry with much more elements, but that would be computationally expensive and not desirable.

I understand that using a hexagonal mesh would greatly improve the solution I would get but with these artery-type geometries, GAMBIT only allows me to build hybrid meshes with tetrahedral and prismatic wall layers.

I have used the double precision solver with the default segregated scheme with residuals up to 1e-10 for the velocities and 1e-9 for the continuity.

Can somebocy help?

Thanks!