Li-Chuan Chen, Marian Muste, and Larry Weber 53:071 Principles of Hydraulics Laboratory Experiment #3 Analysis of Open-Channel Flow Transitions Using Specific Energy Diagram Li-Chuan Chen, Marian Muste, and Larry Weber

Objective To observe the changes in the behavior of the free surface when subjected to changes in the channel bed.

Principle

Principle

Apparatus — Flume

Apparatus — Obstruction 7.78 6.96 5.87 5 0.24 ybump (ft) x (ft) For x  5 ybump = 0 For 5 < x  5.87 ybump = 0.276x – 1.38 For 5.87 < x  6.96 ybump = 0.24 For 6.96 < x  7.78 ybump = 2.28 - 0.293x For x > 7.78 ybump = 0

What are we going to do? We are going to measure the water surface elevation along a open channel.

Procedures Establish a stabilized discharge in the system. Measure the water level difference on the differential manometer for computing discharge. Measure the water surface elevation upstream, above, and downstream of the obstruction. Change the flow rate and repeat Step 2 and 3 for another flow condition. Observe the ripples formed at the tip of the point gage.

Water Surface Elevation (ft) Data Sheet Flow Situation I Flow Situation II h = (ft); Q = (cfs); yc1 = (ft) h = (ft); Q = (cfs); yc1 = (ft) Track (ft) Water Surface Elevation (ft) Bump Geometry (ft) Actual depth Track (ft)  

Analysis Plot the water surface elevation in the vicinity of the channel transition. Construct the specific energy diagram using the measured data. Compare theoretical specific energy diagrams with the experimental curves. Comment on the flow behavior in the two flow situation.

Sample Result — Water Surface Profile

Sample Result — Specific Energy Diagram

Further Considerations What are the main assumptions associated with the use of the specific energy diagram? Comment on the differences noticed on the ripples produced by the point gage upstream and downstream the obstruction. Analyze the water surface behavior for the same unit discharges used in your experiment hypothesizing the flow enters in the obstruction as supercritical flow.