equivalent diameter vs hydraulic diameter
 

hi friends,
i stuck up with one problem. i am working on flow over 2D triangular cylindrical obstacle in a channel. i am planning to compare my results ie drag coefficient, wake length etc., with square obstacle. my question is on what basis i have to compare these two either by equivalent diameter or hydraulic diameter?
also what is the difference between these two diameters?
please reply me...

This is not a comprehensive answer, but I have only seen the hydraulic diameter applied to internal flows, whereas the equivalent diameter is used for representing objects submerged in an external flow.