Illogical problems with fluid flow
 

Hi everyone,
I'm doing research on conjugate heat transfer (transient) in borehole heat exchanger consisting of 2 U pipes (130 m deep). Water inside the pipes, solid region around.
Model is created in Solidworks and meshed in gambit. Both U pipes are creted and meshed in the same way and have same number of elements. Both pipes have interface with solid region. Interface is created with following options: coupled and mapped.

Velocity inlet and pressure outlet are BC with same conditions. Energy and standard k-e convection models are used.


Problem is that on one U pipe data obtained is rather unphysical. Please see attached figure of velocity magnitude. (lines 43&44 is one U pipe, lines 40&41 is the "problematic" pipe).

Is there anyone more experienced who can propose a possible error that can cause such strange behaviour. If any more information is needed, I'll gladly share with you.
From my point of view there is something terrible wrong but I'm not sure where to look and how many steps should I go back (model creation, meshing, fluent set up, etc.)

P.S. I'm new to the forum so please don't hesitate to correct me in my forum "behaviour". Thank you!