Open Channel Flow - Lab Report Example

Open Channel flow Introduction Open Channel flow refers to fluid flow that is exposed to atmospheric pressure. Examples of open channel flow include Half Full Culverts, streams, rivers, etc. In open channel flow, the pressure on the surface of the flow is assumed to be constant. Also, the hydraulic grade line is assumed to be at the surface of the flow. The flow in open channel flow is classified as steady or unsteady. The steadiness or unsteadiness of the flow is greatly dependent on the velocity of the flowing fluid, the discharge and the flow depth.

Steady flow refers to a flow whereby the amount of water entering the channel is equivalent to the amount of water leaving the channel. Steady flow is divided into two classes, uniform steady flow and non-uniform steady flow. For steady flow to be classified as non – uniform steady flow, the average velocities of the flowing fluid in in successful cross sections of the open channel must be the same. This depend on the cross section of the channel. For steady uniform flow to occur, the cross sectional are must be constant.

When the there is a sudden change in the layout of the open channel such as constriction, changes in cross sectional are among others, the flow may gradual or suddenly change. This is non – uniform flow. Non – uniform flows occurs is divided into two classes, gradually varied flows, which occurs in when the change in surface are is small, and rapidly varied flow, which occurs when the change in cross sectional are is large. In most calculation, the flow is assumed to be uniform to determine the properties of the flow.

This flow can be represented using several equations. These equations are the manning’s equation, Chezy’s Equation and Darcy – Weiberschh equation. The equations are as listed below respectively. Using the above listed equations, either singly or in combination, flow properties of any channel can be determined. The laboratory project was mainly done to enable observation of flow characteristics of an open channel, using different equations, which include the manning’s equation, Chezy’s Equation and Darcy – Welbersch Equation.

Using this equations, different friction factors of channels were determined. Methodology The datum for the vernier scale was first set as the datum surface. The Rota meter was then used to calculate the flow rate. The flow rate was then reified using the bucket and the stop watch methods. The depth of the over the smooth channel and each of the rough channel was measured and recorded. The length and the width of the channel was also measured and recorded. The bottom and top depth of each channel was measured and recorded.

Results       Position 1 Position 1 Position 2 Position 2 Position 3 Position 3 Position 4 Position 4 Position 5 Position 5 Group 7 Slope (%) Flow Gauge Q (L/sec) Datum Elevation (mm) Water Surface Elevation (mm) Datum Elevation (mm) Water Surface Elevation (mm) Datum Elevation (mm) Water Surface Elevation (mm) Datum Elevation (mm) Water Surface Elevation (mm) Datum Elevation (mm) Water Surface Elevation (mm) Trial 1 0.7   0 33.8 0 32.8 0 32.2   34.1 0 12.3 A 0 2575.56 0 2499.36 0 2453.64 0 2598.42 0 937.26 P 76.2 143.8 76.2 141.8 76.2 140.6 76.2 144.4 76.2 100.8 R 0 17.

91070932 0 17.62595205 0 17.4512091 0 17.99459834 0 9.298214286 V 0 155.3060305 0 160.0409705 0 163.0231004 0 153.9397018 0 426.7759213 Q(mm3/s) 400000 S 0.007 n 0.003691364 0.003544065 0.003456189 0.003735753 0.000867504 f 0.000120008 0.000114225 0.000110817 0.000121768 2.45927E-05 C 808.6760981 828.895375 841.543901 802.8098806 1786.391685 Mean 0.000098 STDV 0.000041 The data was recorded in the attached excel files Discussion Velocity of flow is usually given as Thus to determine the manning’s, n, N in the equation ids made the subject t of the equation as below.

Where R is the Hydraulic Radius. The hydraulic radius is given by the quotient of area and wetted perimeter like in equation below, A is the are given by the Depth multiplied by the channel width. P is the wetted perimeter which is twice the depth plus the channel width. Like in the equation below The channel with was 76.2 mm Using the above developed formula, the manning’s, n and f were calculating using excel sheet. The results are as shown in the excel document attached. The mean for the roughness value is 0.

000098 and the standard deviation is 0.000041. The experimental values are not the exact values, though they are close to the exact values. This is attributed to errors that may have resulted while carrying out the experiment. Therefore, I’m not confident with the experimental values. The experimental setup had great impact on the results of the experimental. To improve on the accuracy of the experiment’s results, great care must be taken to ensure that there are no errors when reading values.

And also, spillage must be minimized. Conclusion, From the results, it can be seen that the roughness value has a great impact on the velocity of flow. This can is attributed to the resistive effects it gives the flow. Also, it can be concluded that, the Chezy’s value, C and the manning’s value, n varies with different conditions. Works Cited Chanson, Hubert. Hydraulics of Open Channel Flow. Burlington: Butterworth-Heinemann, 2004. Electronic.