Turbulence Parameters

Bob

I have a few questions on setting up turbulence parameters within boundary conditions, especially using 3D. For example, if I have a rectangular duct, would I use the hydraulic diameter(2bh/b+h) or use the height of the duct as my hydraulic diameter. What would be the best method for inlets or outlets with odd shapes, e.g. kidney or trapezoid shaped or say I have a lot of small inlets bound together as an entire inlet boundary? My geometry is that of a annulus combustor. I am modeling one cup of it. Some of the inlets are odd shaped. For those odd shapes would it be better to use a length scale and if so what would my length scale be related to. Would it be related to the cup circumference or the length from inlet to outlet? Any help will be appreciated.