The topic of turbulent flow is too important to be left to incomplete or incorrect advice...
Turbulent flow in heat carrying fluids is almost always desirable.
In the manuals I have read on GSHP design, careful attention is given to the many aspects that contribute to successfully achieving turbulent flow.
I strongly recommend anyone who is seriously contemplating doing a GSHP ground loop, to obtain a copy of a GSHP design manual. They are for sale
HERE and also can be found through your local library, as hikerjohnson has happily discovered. I have also seen them pop up on Amazon.
I personally own the original manual, which has been added to and included in the updated manual.
Even if you are considering hiring out the construction of a GSHP system, I'd strongly advise getting and reading the manual first.
Knowledge is power.
-AC