Steady Fluid Flow Phenomena in Open Channels: Investigation through Laboratory Experiments and Compu

Experimental Methodology

The aim of this assignment is to demonstrate the students� ability to produce a technical engineering report investigating steady fluid flow phenomena in open channels, using both laboratory experiments and computer simulations. As such, the assignment comprises two components:

It is concerned with laboratory investigation of two methods of measuring

open channel flow and hydraulic jumps.

o A.1. Crump weir

o A.2. Broad crested weir

It involves a computer model of gradually varied flow in an open channel (M2 backwater profile).

This part investigates the phenomenon of rapidly varied steady flow in an open channel. This will be based on a laboratory experiment comparing the measurement of flow using a crump.

Weir with that using a broad crested weir, and will also investigate hydraulic jumps occurring downstream from the two weirs, and matching the experimental results obtained from those from theory. Estimates will also be made of the loss of specific energy of the flow over the two weirs. The experimental procedures and required analyses are outlined below:

Experimental Procedure.

1. Verify that the hydraulic bench unit (water tank and pump) has enough water and is connected to the H23 flume water intake.
2. Measure the channel dimensions (width and depth), and ensure that the slope (So) of the flume is cero (So=0%),
3. Install the crump weir at about 800mm downstream from the point at which the water leaves the stilling filter.
4. Turn on the pump of the hydraulic bench, and adjust the flow to its maximum by opening the valve. The water should not overflow from the channel. 5. Obtain the depth of the flow at the following locations by using the depth gauge provided. The depth is the result of the difference of two readings: bottom bed and water surface.
5. Some 100mm upstream of the weir (y1)
6. At the lowest depth at the bottom of the weir (y2)
7. Just before the jump (y3)
8. After the jump where the water is in tranquil flow (y4)
9. Estimate the length of the jump (L), i.e. the distance between y3 and y4.
10. By using the Pitot tube measure the velocity head (if possible) at the same four locations, comment on any difficulties experienced.
11. Measure the flow rate by using the volume gauges built into the hydraulic bench, andthe stop watch provided. It is suggested to record the time that takes to deliver 5 litres of water.

Please note that the tank starts filling when the plug (rubber ball) is blocking the outlet.

In order to reduce the uncertainty and improve the results, measure the flow rate at least 3 times and obtain an average.

Decrease the flow rate by closing slightly the valve and repeat the procedure from point 5. Verify that the depth upstream of the weir decreases at least 5 mm. And repeat this procedure at least 5 times more, every time with a different discharge.

Using that value of volumetric flow rate per unit width ( ), evaluate the specific energy for a range of theoretical depths up to a maximum of 200 mm. Plot these values in a dimensionless form: ( ) versus ( ). On the same curve, plot the values of the and calculated from the measured and in dimensionless form, for the same discharge.

Explain how the graph has been generated and investigate the phenomenon of rapidly varied steady flow in an open channel along with the characteristics of a free hydraulic jump.

• Briefly list the equipment used.
• Experimental set up.
• Tabulated results.
• Raw measurement
• Fully annotated plots and description of it.

Now using the whole 5 experimental results; calculate the ratio , and the Froude number just before the jump in each case. Using this calculated , calculate the theoretical value of . Plot against for both experimental and theoretical CW V.2 results. For fully annotated plots and description of it, including equation for Froude number.

Discuss your results, assessing their validity and reliability, comment on the accuracy and draw the relevant conclusions.

• How valid the equations.
• What were the assumptions for the equations when derived, what human and lab errors were present, accuracy of instruments used etc.
• Draw conclusions.
• For wider implications.

For each case, calculate the flow force across the gate, the head loss across the jump.

A.2. Broad Crested Weir

Repeat the procedures outlined in A.1 using the broad crested weir in the same position as the crump weir was.

1. Calculate the loss of specific energy across each weir and through each hydraulic jump.
2. Calculate the Drag Coefficient of the weir
3. In your conclusion compare the performance of the two weirs as measuring systems for the flow in open channels and discuss this with reference to published work on each weir.
4. Suggest which weir would be used if you needed an accurate measure of irrigation water delivered to an area or a large agricultural business

Comment on the use of hydraulic jumps to reduce the energy in open channel flows:

Fluid flow in open channels is an important topic in civil and hydraulic engineering. Open channels are commonly used for water supply, irrigation, flood control, and transportation of sediments. The hydraulic properties of open channels are critical to the design and operation of such systems. In this report, we investigate steady fluid flow phenomena in open channels using laboratory experiments and computer simulations.

Experimental Methodology

The laboratory experiments were conducted using a flume with dimensions of 1.5 m in length, 0.3 m in width, and 0.3 m in depth. The flume was set up with a water supply system and a discharge measurement system. A flowmeter was used to measure the flow rate, and a pressure gauge was used to measure the hydraulic gradient. The experiments were carried out with different flow rates and channel slopes to investigate the hydraulic properties of open channels.