I am Dhananjay working on Fluid Flow and Heat Transfer Analysis. I tried to find out the fully developed velocity profile for Laminar Flow in a circular cylindrical geometry using STAR-CD version 3.24, which logically should be Parabolic and centre-line velocity in axial direction should be 2 times that of inlet average velocity. I tried with different types meshes viz. Tetrahedral, Hybrid and trimmed. However, I could not get the result. Then I tried to increase the Extrusion layer thickness in radial direction as much as possible. I could see the effect of developing profile and increase in the max centre-line velocity by 1.8 times that of inlet. However, I could not get the result closer to analytical result, by extreme refining of the meshes too. The modelling and grid generation is also checked.What can be the probable reason for this? What is the extrusion layer and its effect?

Please, help me to obtain the result for validation.