The cross section of cipoletti weir
Trapezoidal
Understanding the Cipoletti Weir Cross-Section
A Cipoletti weir is a specific type of flow measurement structure used in open channels. It is designed to provide accurate discharge measurements, particularly by attempting to eliminate the effects of end contractions.
The key feature of the Cipoletti weir, which distinguishes it from a simple rectangular weir, is the shape of its notch or cross-section.
Let's look at the common shapes of weirs:
- Rectangular Weir: Has a rectangular notch with vertical sides. It suffers from end contractions, which reduce the effective width of the flow over the weir.
- Triangular Weir (or V-notch weir): Has a triangular notch. It is particularly useful for measuring low flow rates.
- Trapezoidal Weir: Has a notch with a rectangular base and sloping sides. The Cipoletti weir is a type of trapezoidal weir.
The Trapezoidal Shape of Cipoletti Weir
The Cipoletti weir has a specific trapezoidal shape. This trapezoidal notch is formed by a horizontal crest at the bottom and two sides that slope outwards.
The sides of the Cipoletti weir's trapezoidal notch have a specific slope. This slope is typically set at a ratio of 1 part horizontal to 4 parts vertical (1H:4V). The purpose of this particular slope is to compensate for the reduction in flow caused by end contractions. The increased flow area due to the sloping sides approximately offsets the loss of flow area due to the contractions.
Therefore, the cross section of a Cipoletti weir is trapezoidal.
Important Questions from Open Channel Flow
- A trapezoidal channel carries $5\text{ m}^3\text{.s}^{-1}$ of water under uniform flow condition. The channel has a bottom width of $2\text{ m}$, side slope of $2:1$ (horizontal: vertical), and a bed slope of $1\%$. If the Manning roughness coefficient is $0.03$, the conveyance of the channel, in $\text{m}^3\text{.s}^{-1}$, is
- Two rectangular channels, A and B, join to form a large rectangular channel, C. Each rectangular channel is lined with the same material and has the same bottom slope. The bottom widths of Channels A and B are $2\text{ m}$ and $1\text{ m}$, respectively. If the flow depth in each channel is $2\text{ m}$, the bottom width of Channel C (in m) is ________. (Rounded off to two decimal places)
- Water is flowing at the rate of 15 m$^3$/s through a rectangular channel of 5 m width.
If the acceleration due to gravity ($g$) is 9.81 m/s$^2$, the critical velocity for the flow is ______ m/s (rounded off to three decimal places). A Hydraulic Jump is said to be Oscillating Jump if its Froude number is ________.
The Francis formula for the discharge over cippoletti weir is
