Bulk velocity on parallel lines

Hi all
I have a two layer geometry. On the interface for calculation of mass transfer coefficient I need to Reynolds number how that velocity in reynolds relation for any point is bulk velocity of upper layer. For example on the point of x=.01 m in interface if I want calculate the reynolds number I should have the average velocity of x=.01 m in the upper layer. I hope to anybody can help me. Attached is consist of my geometry.
Best regards;