2D Results different the 3D results
 

I find a big problem when caculated the two-dimension circular pipes model with Star-CCM9.02.When I convert Regions to 2D.The results of the 2D were different from 3D.The volecity(i) in 2D Region si roughly half of the results when caculated in 3D Region directly. The 3D results were close to the literature.

I buit a cylindrical coordinate system.
The physics models: Constant desity
laminar
Gradients
liquid
Segregated Flow
Steady
Three Dimensional
Inlet volecity fild function:1*0.002-10964*0.002*($$Position("Cylindrical 1")[0]*$$Position("Cylindrical 1")[0])

Thanks a lot to give me a help.:)

My teacher told me that :Maybe Star-CCM+ won't use the cylinderical N-S equation when caculated in the 2D plane and did't regard the rectangles as the section of the cylindercial pipes.:confused: