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The wetted perimeter is the perimeter of the cross sectional area that is "wet". [1] The length of line of the intersection of channel wetted surface with a cross sectional plane normal to the flow direction.
P is the wetted perimeter of the cross-section. More intuitively, the hydraulic diameter can be understood as a function of the hydraulic radius R H, which is defined as the cross-sectional area of the channel divided by the wetted perimeter. Here, the wetted perimeter includes all surfaces acted upon by shear stress from the fluid. [3]
where is the cross sectional area of flow and is wetted perimeter. For a semicircular channel, the hydraulic radius would simply be the true radius. For an approximately rectangular channel (for simplicity in the mathematics of the explanation of the assumption), =,
This is the cross-sectional area of the channel divided by the wetted perimeter. For a semi-circular channel, it is a quarter of the diameter (in case of full pipe flow). For a rectangular channel, the hydraulic radius is the cross-sectional area divided by the wetted perimeter.
P is the wetted perimeter (L). For channels of a given width, the hydraulic radius is greater for deeper channels. In wide rectangular channels, the hydraulic radius is approximated by the flow depth. The hydraulic radius is not half the hydraulic diameter as the name may suggest, but one quarter in the case of a full pipe. It is a function of ...
For free surfaces (such as in open-channel flow), the wetted perimeter includes only the walls in contact with the fluid. [ 3 ] Similarly, in the combustion chamber of a rocket engine , the characteristic length L ∗ {\displaystyle L^{*}} is defined as the chamber volume divided by the throat area. [ 4 ]
is the hydraulic radius, which is the cross-sectional area of flow divided by the wetted perimeter (for a wide channel this is approximately equal to the water depth) [m]; is Manning's coefficient [time/length 1/3]; and; is a constant; k = 1 when using SI units and k = 1.49 when using BG units.
Where pf is the free perimeter of the channel (i.e., the interface not in contact with the channel wall), and pw is the wetted perimeter [citation needed] (i.e., the walls in contact with the fluid), and θ is the contact angle of the fluid on the material of the device. [1] [5]