Turbulence intensity in fully devloped pipe flow - Reference
 

Dear Colleagues,
in the CFD-Wiki the following is statet for the turbulence intensity in fully developed pipe flow:

Fully developed pipe flow For fully developed pipe flow the turbulence intensity at the core can be estimated as:
http://www.cfd-online.com/Forums/../...c52357d30b.png Where http://www.cfd-online.com/Forums/../...913bb4a9a4.png is the Reynolds number based on the pipe hydraulic diameter http://www.cfd-online.com/Forums/../...eca9117473.png.



Does someone have a reference (textbook, journal paper, conference paper) for this statement...
It would really help me to find out where it comes from...
THX