Open Channel Flow Experiment: Discussion, Conclusion

Open Channel Flow Experiment: Discussion, Conclusion


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Introduction: Open Channel Flow Experiment

An open channel is a duck which has a free surface exposed to the atmospheric pressure. Hence the pressure at the surface is constant and flow can only generate by the slope of the surface by potential energy changes. The open channel allow a series of experiments on water flow through a rectangular channel. There is an adjustable sluice gate at the end of the channel which allows to control the outlet flow. Open flow channel can be used to verify Chezy formula and the manning formula as well as it allows to investigate flow characteristics of hydraulic jump, effects of different types of weirs and flumes.  In theses series of experiments, a triangular hump weir, venturi flame, sharp crested wear and a broad crested weir are used to investigate the flow characteristics under different conditions.(Open Channel Flow Experiment)

Results and Analysis

Experiment 1 – Flow in Open Channels

Aim

To investigate the flow of water through a rectangular open channel.

Procedure

  1. The Hydraulics Bench was assembled in accordance with the thorough instructions provided.
  2. The sluice gate at the discharge end of the canal was entirely lifted up, preventing flow limitation.
  3. The flow channel slope was adjusted at a downward gradient of 0.125 in 150 from left to right.
  4. After turning on the Hydraulics bench pump, the flowrate was set to around 1.5 liters per second.
  5. When the flow conditions had stabilized, the flow rate was measured using the hydraulics bench’s volumetric tank. Following that, the depth of water in the flow channel was measured 50cm from the left end.
  6. The technique described above was performed for a variety of various downhill grades while maintaining a consistent flowrate at all times.

Results and Analysis

Results and Analysis
Results and Analysis
Results and Analysis

Discussion : Open Channel Flow Experiment

The experiment demonstrates how the characteristics of a water flow may alter. A free surface is present in an open flow. As a result, the pressure acting along the flow remains constant. There are two sorts of flow conditions: steady flow and unstable flow. If the amount of water entering is about equal to the amount of water leaving. Such flows can be classified as either uniform or non-uniform. The collected data suggest that raising the slope improves the output flow rate. The graphs illustrate that when mean velocity declines, so decline (√(𝐷𝐻𝑀 βˆ— )) and

(𝐷𝐻𝑀3/2 βˆ— βˆšπœƒ).

Conclusion : Open Channel Flow Experiment

Values for the measure flow rate were recorded using flow meter and value of theoretical flow rate was calculated by using manning equation. Difference between the values of these two flow rates is because the theoretical flow rate depends on the slope of the channel bed and also on the other factory like manning roughness coefficient but the measure flow rate depends only on the area and velocity of the fluid through that area. Applying the same flow rate at different slopes has shown that the change in the slope of bed change the theoretical flow rate value as it depends on the depth of the flow. 

Experiment 2 – Flow Under a Sluice Gate

Aim

To investigate the flow of water under a sluice gate.

Procedure 

  1. The Hydraulics Bench was set up in accordance with the detailed instructions provided.
  2. The sluice gate was installed in the channel at a distance of 50cm or more from the water flow entry.
  3. The sluice gate at the discharge end of the canal was entirely lifted up, preventing flow limitation.
  4. After turning on the Hydraulics bench pump, the flowrate was set to around 1.5 liters per second.
  5. It was then determined whether steady circumstances had been attained at the upstream measuring location. Once such steady circumstances were created, the water depth was measured at the specified measuring stations.

The water depths were measured at the following locations:

  • 20cm upstream of sluice gate
    • 10cm downstream of sluice gate
    • 20cm downstream of sluice gate
  • The width of the flow channel was then measured at each of the three abovementioned measuring stations.

Results and Analysis

𝑄2

  𝐸 = 𝐷 + 2

2𝑔𝐴2

Critical points –                                         𝐸𝑐 =  π·π‘

Results and Analysis
Results and Analysis

Discussion : Open Channel Flow Experiment

The flow through a channel in which a gate partially obstructs the flow will be used for this measurement of total force. This obstruction is called a sluice gate. Three assumptions will be made in this derivation of the equation for horizontal force on a sluicegate the viscous force at the bottom of the channel and the energy dissipation at the gate are negligible, the flow is steady and has a uniform velocity distribution at the inlet and outlet sections, Flow at upstream and downstream sections is uniform and the effect of the side-walls is negligible.

Conclusion : Open Channel Flow Experiment

The experiment verified to be successful because it was determined that the theoretical fluid analysis can be used to define the velocity downstream of the Sluice Gate, the Head change of the flow and the depth downstream of the hydraulic pump. There was some variation between the theoretical and measure values due to various factors such as; friction and loss of mechanical energy due to viscosity.

Experiment 3 – Demonstration of a Hydraulic Jump

Aim

To investigate the phenomenon of a hydraulic jump.

Procedure : Open Channel Flow Experiment

  1. The flow channel was configured similarly to the experiment. 2.
  2. The sluice gate at the discharge end of the canal was entirely lifted up, preventing flow limitation.
  3. After turning on the Hydraulics bench pump, the flowrate was set to 1.5 liters per second.
  4. The height of the sluice gate was adjusted until the bottom of the sluice gate touched the water surface, and then it was connected to the discharge end of the flow channel.
  5. Once a hydraulic jump was produced, the discharge sluice gate was fine-tuned until the hydraulic jump was steady and stationary between the two sluice gates.
  6. Finally, the water depth was measured on each side of the hydraulic jump.

Results and Analysis

Flow rate = 26.6 l/min

Width (B) = 7.7 cm

𝑄2

𝐸 = 𝐷 + 2𝑔𝐴2

Before to the jump the Depth of the water (D) = 1.4 cm

Flow area = 10.78 cm2

Specific energy = D + Q2/2gA2 = 0.014+ (4.43*10-4)2/2*9.81*(10.78*10-4)2 =

0.0226 m

After to the jump the Depth of the water (D) = 1.6 cm

Flow area = 12.32 cm2

Specific energy = D + Q2/2gA2 = 0.016+ (4.43*10-4)2/2*9.81*(12.32*10-4)2 =

0.0225 m

Discussion : Open Channel Flow Experiment

Practical applications of hydraulic jump are growth weight on an apron and decrease uplift pressure under a structure by raising the water depth on the apron, To indicate special flow conditions such as the existence of supercritical flow or the presence of a control section so that a gaging station maybe situated, To increase water level on the downstream side for irrigation or other water supply determinations. To mix chemicals used for water purification.

Conclusion : Open Channel Flow Experiment

The conclusion from the experiment, we can examine the characteristic a standing wave (the hydraulic jump) produced when waters beneath an undershot weir and to observe the flow patterns obtained. From the experiment, we can get the force at weir opening. In the water channel, water flowing rapidly changes to slower tranquil flow hydraulic jump or standing wave is produced. This phenomenon can be seen where water shooting under a sluice gate combination with deeper water downstream. It happens when a depth less than critical changes to a depth which are greater than critical and must be complemented by loss of energy.

Experiment 4 – Flow Over a Triangular Weir

Aim

To investigate the flow over a triangular hump weir.

Procedure : Open Channel Flow Experiment

  1. The Hydraulics Bench and flow channel were set in accordance with the comprehensive instructions provided.
  2. The triangular weir was placed in the canal about 500mm from the location where the water flow entered.
  3. The position of the measurement points, numbered 1 to 12, was determined using the given lab manual.
  4. The sluice gate at the discharge end of the canal was entirely lifted up, preventing flow limitation.
  5. After turning on the Hydraulics bench pump, the flowrate was set to around 1.5 liters per second.
  6. Once stable conditions at the specified flow rate have been established; ● The heights of the water surface at the measuring positions from 1 to 12 were measured and recorded to a results sheet. 

● Using the volumetric tank of the hydraulics bench, the flow rate was measured.  7. The flow rate was then adjusted to approximately 0.5 liters per second, and the flow rate as well as the location of the water surface were precisely monitored

Results and Analysis

𝑄2

𝐸 = 𝐷 + 2𝑔𝐴2

Trial 1 Flowrate = 4.42*10-4 m3/s

Trial 2 Flowrate = 1.40*10-4 m3/s

Width (B) = 7.7 cm

Results and Analysis
Results and Analysis
Results and Analysis

Discussion : Open Channel Flow Experiment

A flow channel model and a triangular notch were used in this experiment to examine and assess the results of variations in water flow as it flows over a triangular hump weir. Although increasing the flow rate, the discharge coefficient using the triangular notch produced correct values for the theoretical value. This resulting value may be influenced by a higher flowrate or larger streams not clinging to the notch. In situations where the water stream clings to the triangular notch, the flow velocity could have been reduced, resulting in lower heights above the notch and greater differences in the theoretical values and equations.

Conclusion : Open Channel Flow Experiment

The smooth flow to and over the weir is essential to the determination of accurate rates of flow since the distribution of velocities on the approach flow has a definite influence on the discharge over the weir. As the flow rate increases, the discharge coefficient becomes more accurate to the theoretical value. When the flow rate is to low it clings to the notch and flows down it. This changes the coefficient of discharge because now the water is not only being affected by gravity it has to resist viscosity and the friction of the surface of the notch. The limitations of the theory is it has to be level so the only force on the water is gravity, there has to be a constant flow, and constant pressure. The theory behind this experiment marks an assumption that there is a minimum height of water above the notch and any heights below this start to deviate from theory at an increasing rate. The relationship between the head of the weir and the discharge of the water over the weir is directly proportional. The lower flow rates produce lower heights above the notch creating larger changes from the theoretical equations.

Experiment 5 – Flow Through a Venturi Flume

Aim

To investigate the use of a venturi flume as a flow measuring device in open flow channel.

Procedure

  1. The Hydraulics Bench was assembled in accordance with the thorough instructions provided.
  2. The flow channel was altered such that the channel bed was horizontal.
  3. The venturi flume was then positioned and put in the flow channel 50cm distant from the water flow entry by positioning two venturi flume halves against the channel walls.
  4. The internal calipers were used to measure the average width of the flow channel as well as the average width of the throat of the venturi flume.
  5. The sluice gate at the discharge end of the canal was entirely lifted up, preventing flow limitation.
  6. After turning on the Hydraulics bench pump, the flowrate was set to 1.5 liters per second.
  7. When the flow conditions had stabilized, the flow rate was measured using the hydraulics bench’s volumetric tank.
  8. The height of the water at the venturi flume’s entrance point was then measured.
  9. The flow rate was then lowered in stages of approximately 0.2 seconds per second down to 0.2 seconds per second. The water flow rate and entrance water height were monitored and recorded at each stage.
Results and Analysis
Results and Analysis
Results and Analysis

Discussion : Open Channel Flow Experiment

The Venturi flume test was performed in this lab experiment, and the constant for each flume, as well as its theoretical values, were determined. The values can be incorrect or slightly different from the right values due to observer errors. The venturi flume test has a few drawbacks in this situation, such as how the upstream depth that was discovered is just a provisional approximation and it is all based on the human reader’s judgment. Another consideration was how to replicate equivalent flow speeds and upstream depths when the flow rate wheel did not have a fixed flowrate. With these constraints, taking proper steps to minimize the above errors can result in values that aren’t too far off from the correct values.

Conclusion : Open Channel Flow Experiment

From this hydraulic investigation, it is noted that there at all times significant energy losses to overcome an obstruction. it can be determined that constrictions in channels can control the upstream and downstream conditions. Frictional forces also take part in the reduction of total and specific energy as water flows through the channel. Finally, the kinetic energy estimated in the channel is much lower than the real kinetic energy of the flow.(Open Channel Flow Experiment)

Experiment 6 – Flow over a Sharp Crested Rectangular Weir

Aim

To investigate the flow over a sharp crested rectangular weir.

Procedure : Open Channel Flow Experiment

  1. The Hydraulics Bench was assembled in accordance with the thorough instructions provided.
  2. The flow channel was altered such that the channel bed was horizontal.
  3. Install the Sharp crested weir in the flow channel.
  4. Set up the fitting clamps.
  5. Fully lift the sluice gate at the channel’s terminus.
  6. Started the Hydraulic Bench water pump and set the flow rate to 37.9 l/min.
  7. After the flow conditions had stabilized, the flow rate was measured in the Hydraulic Bench with a 1000 ml measuring cylinder.
  8. The height of the water surface was measured at the flow’s entrance point.
  9. When the flow rate was reduced, the following processes were repeated.
Results and Analysis

Discussion : Open Channel Flow Experiment

The result table shows that when the inflow flowrate falls, so does the specific energy, as does the water head depth. This is due to energy loss caused by frictional forces. Potential energy is converted into kinetic energy.

Conclusion : Open Channel Flow Experiment

As we can see, as the output flow rate exceeds the entrance flow rate, the velocity of the flow rises over the weir. We can also see that specific energy varies as the flow rate and specific energy rise.  The coefficient of discharge fluctuates during the experiment because H values fluctuate.  

Experiment 7 – Flow over a Broad Sharp Crested Weir

Aim

To determine the relationship between upstream head and flow rate over a Broad Crested Weir and to calculate the discharge coefficient and observe the flow patterns over the weir.

Procedure : Open Channel Flow Experiment

  1. The Hydraulics Bench was assembled in accordance with the thorough instructions provided.
  2. The flow channel was altered such that the channel bed was horizontal.
  3. Next, the weir was placed in the channel, with the round edge upstream.
  4. One of the depth gauges was then used to measure the height of the weir above the channel bed.
  5. One depth gauge was set downstream of the weir, while the other was positioned upstream of the weir at a specified distance.
  6. The flow was then gradually modified to acquire values for E (in 10mm increments), and the flow rate was measured in the upstream depth above the weir and the depth above the weir for each value.
  7. When the flow conditions had stabilized, the actual flow rate was measured using the hydraulics bench’s volumetric tank and a timer.
Results and Analysis
Results and Analysis
Results and Analysis

Discussion 

We employed a broad crested weir and depth gauges in the experiment to observe and estimate the link between upstream head and flow rate over a broad crested weir, as well as to compute the discharge coefficient and analyze the flow patterns over the weir. The discharge coefficient is proportional to the flowrate Q, as shown in the table. The discharge coefficient dropped as flowrate increased, and vice versa. It is also partially influenced by the weir height. The flowrate or velocity is zero at the weir’s surface because the water flow clings to the surface owing to frictional factors. Drowning the weir would result in a drop in critical depth and a transition of energy from potential to kinetic.

Conclusion

The boundaries of the theory is it has to be level so the only force on the water is gravity, there has to be a constant flow, and constant pressure. The theory behind this experiment makes an assumption that there is a minimum height of water above the notch and any heights below this start to deviate from theory at an increasing rate. The relationship between the head of the weir and the discharge of the water over the weir is directly proportional. The lower flow rates produce lower heights above the notch creating larger changes from the theoretical equations.

Experiment 8 – Flow over a Free Overflow Spillway

Aim

To observe the flow patterns associated with water flowing over dam spillways  

Procedure

  1. The Hydraulics Bench was assembled in accordance with the thorough instructions provided.
  2. The flow channel was altered such that the channel bed was horizontal.
  3. Water was pushed into the flume’s upstream end until it was just running over the spillway’s crest.
  4. The total of h and was determined by determining the water level some distance upstream of the spillway.
  5. The spillway discharge was then measured by timing the passage of a known volume of water into the hydraulic bench’s volumetric tank.
  6. Measurements were taken again and again while gradually increasing the values of pumping rate (Q) and head (h) in 5mm increments.
  7. Next, the spillway’s head versus discharge relationship was plotted and compared to the previously recorded feature of the sharp crested weir.

Results and Analysis
Results and Analysis

Discussion 

When the rectangular siphon duct functions with the entire section free of air bubbles, the task is regarded accomplished priming, and therefore it is possible to end. A simple distinction of no complete priming regions is created for low head values applied to the level upstream of the siphon.(Open Channel Flow Experiment)

Conclusion

The discharge capacity of a Creaser-profiled weir and siphon spillway was theoretically recalled and empirically tested. The comparison of siphon spillway and weir models enabled the fields to be defined based on the value of the ratio h/a, with the siphon regarded to be better at evacuation than the weir under the same flow circumstances and vice versa. Finally, the study demonstrates linear and nonlinear correlations between the flow over the weir and the siphon spillway, also known as an overflow spillway.(Open Channel Flow Experiment)

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