English term
hydraulic tunnel height
I couldn't understand the meaning of hydraulic tunnel height.
actually I don't understand "the ratio of 4 times....perimeter" either though.
Can someone explain the meaning for me? thank you in advance
Jul 8, 2015 09:48: Charles Davis changed "Level" from "Non-PRO" to "PRO"
PRO (3): Edith Kelly, Coqueiro, Charles Davis
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Responses
Nominal height of a tunnel for carrying water
If the cross section is circular, the height of the tunnel would be the diameter of the circle. This is the same as "the ratio of 4 times the tunnel cross- sectional area to the tunnel perimeter" (4 * (pi * d * d /4) / ( pi * d)).
Likewise, if the cross section is a square of edge length l, the height of the tunnel is l, which is also 4 times the cross-sectional area divided by the perimeter ( 4 * l * l / (4 * l) ).
I suspect the cross section of actual tunnels is a different shape, most likely an ellipse of low eccentricity (so it is close to a circle), and perhaps it is not uniform, i.e. it varies (slightly) along the length of the tunnel. In that case, the proposed ratio would give an approximate measure of the height of the tunnel.
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Charles Davis
: Hydraulic doesn't mean it's carrying water, or a liquid at all. Fluid includes gas. It is the nominal height (or diameter) used to calculate flow (esp. turbulent flow), in this case of a gas (air), through a tunnel with non-circular cross-section.
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Reference comments
Info
[...]
Fig. 2 shows a plot of existing experimental data on the critical ventilation velocity as a function of the heat release rate in fire tunnels. The tunnel size is expressed by the hydraulic tunnel height, ̄H, defined as 4 x (cross-sectional area)/(perimeter). The values of ̄H range from 0.18 to 7.72 m, a factor of 43
[...]
The introduction of the hydraulic tunnel height ̄H effectively absorbs the parameter W [11]. As long as the channel cross-section does not deviate too far from a square, approximate geometrical similarity is maintained. Since the aspect ratio of the tunnels used in the practical application are not too large, an extrapolation of small-scale results is approximately valid.
[...]
:
http://www.cdc.gov/niosh/mining/UserFiles/works/pdfs/cvvit.p...
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Note added at 2 Stunden (2015-07-08 08:18:02 GMT)
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The hydraulic diameter, DH, is a commonly used term when handling flow in noncircular tubes and channels. Using this term one can calculate many things in the same way as for a round tube. It is defined as
D_H = 4A/P
where A is the cross sectional area and P is the wetted perimeter of the cross-section.
The Manning formula contains a quantity called the hydraulic radius. Despite what the name may suggest, the hydraulic diameter is not twice the hydraulic radius, but four times.
Hydraulic diameter is mainly used for calculations involving turbulent flow. Secondary flows can be observed in non-circular ducts as a result of turbulent shear stress in the turbulent flow.
Hydraulic diameter is also used in calculation of heat transfer in internal flow problems:
https://en.wikipedia.org/wiki/Hydraulic_diameter
| thank you. Your reference information helps a lot! |
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