Experiment 1: February
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20, 2010
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Setup
Our This experiment consisted of a very simple setup. The manifold we designed is a 10' long, 6" PVC pipe with 1" diameter holes drilled every 5cm. The manifold had water pumped through it at a rate of 3.8 L/sec (roughly 1 gallon/min) and the water flows through a whole 10' section of 6" PVC pipe before it gets to the manifold to ensure that the effects of the pump have dissipated in the pipe. The manifold is suspended 14" above the bed of the flume by U-clamps and the manifold is spaced 7" from the flume wall to make sure that it runs straight in the flume. The ports of the manifold are positioned so that the jets exiting from them run parallel to the bottom of the tank.
The ADV used to take velocity readings was mounted to a beam running across the width of the flume. The ADV was positioned so that it was aimed head on into the ports (so it also lies parallel to the bed of the flume) at a fixed distance of 17 cm from the port openings.
The measurements were taken at 4 different points along the manifold, separated into at close to fourths as possible given the interference of bolts protruding from the walls of the flume. For each port, we manuevered the ADV in front of each port until we thought we were in the the peak portion of the flow. We recorded data for 1 minute and then moved the ADV 1 cm to the left and 1 cm to the right of our first recording point to ensure that we captured the peak flow. We collected data at these points for 1 minute also.
one 10' Manifold with 1 in. holes drilled every 5 cm on one side of the pipe. This resulted in an Am/Avc = 1.
Procedure
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h5. Figure 1: Example of the Velocity Profile across a port
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The main objective of the lab experiments was to measure the average water velocity coming out of the ports in the vena contracta region. Due to difficulty to ensure that the measured point was the point interest, three measurements were taken for each port. One measurement was done in the center of the port and one to each side of the port, 1cm apart. The purpose of the three measurements was to graph an approximate flow profile across each port and according to the results estimate what would be the water flow velocity in the vena contracta region. An example of the graph flow profile for each port is shown in the following graph.
The highest velocity estimated from the equation obtained from the trend line was taken as the velocity in the vena contracta. Although this value is not correct, the relative values between ports could give us good idea what is the actual behavior of the velocity through the ports.
For this experiment measurements were taken in five ports (3, 16, 27, 38 and 52) and each measurement had around 1 minute of data information.
Results & Discussion
The results of our first experiment for a uniform manifold were not what we expected. Due to the expectation of pressure recovery dominating major losses (friction inside the manifold) we had expected the velocity coming out of the ports to actually increase along the length of the manifold. See Figure 2 for a graph of the theoretical results that we expected. However, once the maximum velocity for each port was plotted against its distance down the manifold (see graph) it seemed that just the opposite trend was true. The velocity appeared to have peaked early on in the manifold and then gradually decreased after that.
Figure 2. A graph of theoretical results assuming the pressure recovery phenomena and assuming no phenomena, observed results
After comparing the lab results with the expected theoretical results and discussing the experimental procedure between Monroe and the group, we conclude that the experiment's measurement procedure was inaccurate and questionable. These results could not give us strong arguments to prove false the presence of pressure recovery in the manifold.
Taking this into account the next experiment was to be done with more measurement points per port and less separation between measurements in order to reduce ambiguity of the results and understand water flow behavior inside the manifold in a more precise wayIn the analysis of our data, we took the mean of the velocities at each port for all 3 (and sometimes 4) measurements. Then we plotted the velocity profile for each port, assuming a Gaussian profile, and estimated the maximum flow rate at each port. These calculations were than plotted along the length of the manifold to give a velocity profile for the uniform manifold setup.