Winter 2024 Department of Civil and Environmental Engineering CE 362L Experiment 4: Hydraulic Jump Introduction The purpose of this experiment is to analyze hydraulic jumps in a rectangular open channel. Depth observations will be used to measure the energy loss caused by the jump. The Froude number will be used to characterize the behavior of the jump. Each student should analyze the provided data and upload a completed worksheet in Canvas before the deadline. Theory Hydraulic jumps, observed as a step-like increase in fluid depth, occur when a flow rapidly shifts from supercritical to subcritical conditions. Often two flow regimes exist in an open channel (supercritical conditions induced by a sluice gate and subcritical further downstream due to an obstruction, for example) and a hydraulic jump serves as the transition between the two types of flow. A significant amount of energy is dissipated in a hydraulic jump due to the intense turbulent mixing that occurs, and they therefore are employed in civil engineering structures to that end. Analysis of hydraulic jumps requires consideration of the momentum, mass, and energy equations. After some manipulation (see your book) we have: And moreover: = 2 1 + √ |1 + 8Fr₁ 2 2 h L = 1 y Fr 1 1 У1 У1 2 2 (Equation 1) (Equation 2) Where y₁ and y₂ are the depth upstream and downstream of the jump, respectively. Fr is the Froude number, and h¸ is the headloss caused by the jump. Note that the physical structure of the hydraulic jump depends only on the Froude number. Recall that Fr = V √gy Here we will measure the depth ratio and energy loss for hydraulic jumps to observe their functional relationship with the Froude number. 1 Winter 2024 Department of Civil and Environmental Engineering CE 362L Apparatus This experiment will be conducted in the flume with a sluice gate to generate supercritical flow. An obstruction will be used to obtain subcritical flow downstream of the gate. A hydraulic jump will then form between these two regimes. There are two sluice gate configurations. Flow rate can be determined using a weir or a paddlewheel flow meter. Assume friction and the slope of the channel are negligible. Procedure The experiment will be conducted with two (2) sluice gate configurations. For each sluice gate (small or medium) measurements will be taken at three (3) different flowrates. 1. Measure the dimensions of the channel. Record the height of the sluice gate opening. 2. Turn on the pump and adjust the flow rate as necessary. Record the flow rate after the system has reached a steady state. 3. Insert one of the gate sections and adjust the downstream obstruction as necessary to create a steady hydraulic jump. 4. Measure the water depth before and after the jump. 5. Repeat steps two through four for the other sluice gate at two additional flow rates. 6. Turn off the pump. Repeat procedure with the second sluice gate. 2 Winter 2024 Department of Civil and Environmental Engineering CE 362L Hydraulics Lab 4 Worksheet Name: Please write answers to the following questions in the space below or on separate paper. Attach tables and figures at the end. Turn in the completed packet as a single pdf file uploaded to Canvas by the deadline. 1. Why are flumes used for studying debris flows? 2. Complete the attached Table 1 for the 6 experimental cases (or prepare your own and attach it). Calculate the approach Froude number, head loss, and theoretical depth after the jump. 3. Create two specific energy diagrams for the measured flow rates, one figure for each sluice gate. Each figure will have three curves, one for each flowrate. On these same diagrams, plot (as individual points) the specific energy before and after the jump for each combination of sluice gate opening and flow rate. 4. Is the approach Froude number ever less than one? Why or why not? 3 Winter 2024 Department of Civil and Environmental Engineering CE 362L 5. Which size sluice gate (small or medium) is more efficient at dissipating energy? Explain. 6. Compare the measured and calculated depth downstream of the jump in each scenario. Ignoring measurement errors, explain any discrepancies. 7. Explain how hydraulic jumps can be utilized in hydraulic structures. Choose an example and be specific. 4 Winter 2024 Department of Civil and Environmental Engineering CE 362L Table 1: Effect of sluice gate height and flowrate on depth, Froude number and headloss. Sluice Q Gate (L/min Height Q (m³/s) Measured Width, b Measured Depth, yo Measured Depth, Y1 (m) (m) Measured Depth, Y₂ (m) (m) (m) Fr₁ Before Jump Calculated Headloss Depth, Y₂ (m) (m) 5/n