The 17-meter flume at the Coastal Research Laboratory. Part II, Flow characteristics : technical report
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Abstract:
Funding was provided by the Minerals Management Service under contract Number 14-12-0001-30262; Sea Grant under contract Number NA86AA-D-FG090; and the Office of Naval Research Young Investigator Program under contract Number N00014-86-K-0579.Keywords:
Flume
long throat flume is recommended nowadays to use in flow rate measurement in irrigation areas for its several advantages over other types of flumes known: ① with a simple flow rate table determined on the flume dimensions, errors of measurement results can be controlled to be less than 5%; ② water head loss over the flume is minimal; ③ this type of flume is suitable nearly to any kinds of channel and is nearly free from floating debris effects.
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A series of detailed laboratory measurements were made under steady-state flow conditions through a 0.914-m (3-ft) Cutthroat flume in an attempt to more accurately define transition submergence for four standard throat widths. It was found that the change from free to submerged flow, and vice versa, is gradual and that there is no easily observable transition point. The gradual transition between the flow regimes suggested a new calibration approach in which a single equation could more elegantly and more accurately fit the laboratory measurements, eschewing the need for separate free- and submerged-flow equations, and obviating the need to define transition submergence. Such an equation was found, providing greater calibration accuracy up to 95% submergence in 0.914-m Cutthroat flumes.
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Free flow
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A study was conducted to revise the procedure for adjusting discharge measurements in a cutthroat flume subjected to settlement in free-flowing conditions. A series of 57 tests was performed on six different size cutthroat flumes. Each flume was systematically adjusted to simulate settlement in both the lateral and the longitudinal directions. Discharge inaccuracies were then recorded for each settlement condition. The test results were combined with the results of three cutthroat flumes previously reported. The coefficients describing the flume geometry, Cdlat and Cdlong, were determined to be significantly different than previously indicated. New expressions for Cdlat and Cdlong were formulated for inclusion into the previously reported discharge measurement adjustment procedure.
Flume
Settlement (finance)
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A Montana flume is a Parshall flume without a diverging downstream section and is used to measure open channel flow. Under free-flow conditions, the Parshall flume and the Montana flume have the same calibration characteristics, but under submerge flows, their calibrations significantly differ. Tests were conducted at the Utah Water Research Laboratory on an acrylic 15.2-cm (6-in.) Montana flume to determine the effects of submergence on the flow readings. This type of investigation has not been previously analyzed. It was found that a standard Parshall flume rating curve overpredicted flow rates in the submerged Montana flume, up to 48%. Parshall submergence corrections were applied to the submerged Montana flume, and flow rates were underpredicted by up to 19%. This study has developed submerged flow rate correction factors specifically for a Montana flume, and the paper also demonstrates how to apply the corrections.
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