Hydraulic Jumps

NOTE: This experiment uses a relatively powerful submersible pump. The pump should only be plugged into a GFCI outlet to minimize electrical risks. Ensure that no other A/C powered devices are operating near the experiment.

1. Fabrication of open-channel flow facility and tank (see diagram and photograph, Fig. 3)

1. Cut lengths of ~6.0 mm thick × 9.5 cm wide clear acrylic sheet with the following lengths: 2×15 cm, 2×25 cm, 1×34 cm, 1×41 cm (Fig. 3a). It is recommended to use a table saw or laser cutter to ensure that the edges are relatively flat and the sheets have equal thickness.
2. Cut holes in the lower right corners of the two 60 × 45 cm acrylic sheets to mount the flow meter (Fig. 3a). Cut a hole on the upper right side of the front sheet to install the flow control valve.
3. Use acrylic cement (e.g., SCIGRIP 16) to bond the acrylic panels as indicated in Fig. 3a. Ensure adequate ventilation and wear gloves when handling the acrylic cement. It is helpful to apply cement with a needle syringe and use masking tape to position panels during curing. Allow the cement to cure for 24 - 48 hours.
4. Install the flow meter on the front panel and affix with the provided screws. Install 1 NPT to ½ NPT reducing fittings on the flow meter inlet and outlet ports. Install ½ NPT to 0.5 in. inner diameter barbed fitting adapters to those fittings.
5. Install a 0.5 in. ID and a 0.75 in. ID barbed fitting onto the gate valve (flow rate control). Connect the barbed fitting to the submersible pump with a ~20 cm length of tubing so that the valve handle lines up with the hole on the top right of the acrylic enclosure (Fig. 3b-c).
6. Insert the pump into the lower reservoir, and install the valve so that the valve stem passes through the mounting hole and the handle is outside the enclosure (Fig. 3c).
7. Insert a vertical acrylic panel near the inlet portion of the flow facility so that there is approximately a 5.0 mm opening below it (Fig. 3b-c). This component will act as the sluice gate, and can be raised and lowered to control flow from the upper reservoir to the channel.
8. Fill the upper reservoir loosely with a stainless steel wool scouring pad. This helps distribute inlet water flow evenly across the channel.
9. Connect the valve outlet to the flow meter inlet with a length of soft plastic tubing. Connect the flow meter outlet to the upper reservoir with plastic tubing. Ensure that the tubing inlet to the upper reservoir is well anchored so that it does not swing out when the pump is turned on.
10. Fill the lower reservoir with water.

2. Performing experiment

1. Measure the gap height underneath the gate using a ruler, and denote the value as H₁.
2. Turn on the pump, and adjust the flow rate using the valve to various flow rates (5 - 15 l min^-1). Use a ruler to measure the liquid depth downstream from the gate (H₂) for each case.
3. Qualitatively observe the shapes of the hydraulic jumps that form at different flow rates. Watch for the minimum threshold flow rate for formation of a hydraulic jump. Sharper, greater amplitude (H₂ -H₁), jumps should occur at higher flow rates.

3. Data Analysis

1. For each flow rate case, calculate the inlet velocity, V₁, from the volumetric flow rate. where is the volume flow rate and W is the channel width.
2. Evaluate the inlet Froude number () and theoretical downstream liquid depth for each case (Eqn. 4). Compare these values with measured downstream jump depths.

Figure 3: a. Schematic and dimensions of facility structure. b. Flow diagram of hydraulic jump facility. c. Labeled photograph of experimental facility.