Archive for category Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices

Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices

Posted by dickinsonre in Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices on October 2, 2010

Note: Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices

The Critical height is the opening where weir flow turns into orifice flow. It equals (Co/Cw)*(Area/Length) where Co is the orifice coeff., Cw is the weir coeff/sqrt(2g), Area is the area of the opening, and Length = circumference of the opening. For a basic sharp crested weir, Cw = 0.414. All of the units are based on the internal SWMM 5 units of American Standard.

For a circular orifice the Critical Height is:

Critical Height = Orifice Discharge Coefficient / 0.414 * Orifice Opening / 4

For a rectangular orifice the Critical Height is:

Critical Height = Orifice Discharge Coefficient / 0.414 * (Orifice Opening*Width) / (2.0*(Orifice Opening+Width))

The Orifice Critical Depth changes dynamically as the orifice is opening and closing for a bottom outlet orifice. The critical depth separating the orifice weir flow from orifice flow for a side outlet orifice is the height of the orifice.

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