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Introduction

The Bernoulli flow experiment has been used at Rochester Institute of Technology for many years. It is a staple experiment performed by senior students in the Thermofluids Laboratory course. In the past, students have expressed frustration in obtaining meaningful results from the experiment. Some past students have called it “an exercise in futility,” and others have failed to use the raw data in meaningful ways. Other students have even suggested changing the design of the channel to a circular cross section. This investigation was performed to elucidate an interesting phenomenon observed when analyzing the raw data. Moreover, this investigation will help future students better understand the experiment, and it will be used in an advanced fluid mechanics course for engineering technology students.

The experimental procedure is typically performed by first obtaining a steady fluid level in the inlet tank, and then various flow rates can be obtained by adjusting an outlet pipe. After obtaining a steady flow rate, students typically record the water height in 11 manometer taps equally spaced along the length of the channel. Next, the fluid is allowed to collect in a basin whereby the volumetric flow rate is recorded using a clear sight glass with a scale and a stopwatch. This is typically done several times, and the average volumetric flow rate is then calculated. When analyzing the raw data, students typically plot the change in pressure head vs. distance for the various turbulent flow rates. Students also plot the change in kinetic energy vs. distance.

This investigation beganafter evaluating the total energy, ideal head and calculated head losses. Calculated head losses decrease after the channel throat and in turbulent flow become negative. This is not expected, because the fluid cannot convert kinetic energy into pressure energy without appreciable positive head losses. Several experiments were then performed along with attempting numerical simulations to investigate and elucidate this phenomenon. Next, the experiments and their results will be discussed. The process of determining the root of the strange results and the current status of the project will also be outlined.

Initial Experiment

The first step in this investigation was to run the Bernoulli flow experiment “as-is” and attempt to replicate the results of past students. Figure 1 shows the P6231 Bernoulli apparatus along with the test bench. The P6100 hydraulics bench consists of: P6103 constant head inlet tank, P6104 variable head outlet tank, variable speed centrifugal pump, and volumetric measurement tank. Initially, a total of eight different flow rates were run, and each consisted of five volumetric flow rate trials. This was done in an effort to eliminate any measurement errors that could occur while reading the volume sight glass. The manometer heights were recorded for each flow rate using the 1/16th inch scale on the Bernoulli apparatus. Figure 2 shows a section view of the apparatus with the numbered manometer taps. The fluid enters on the left side of the channel from the P6103 inlet tank, then travels from taps 1 to 11 and finally exits into the P6104 outlet tank.

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Schultz, J., & Villasmil, L. (2009, June), Reconciliation Of Bernoulli’s Equation In Channel Flow: An In Depth Empirical And Numerical Approach Paper presented at 2009 Annual Conference & Exposition, Austin, Texas. 10.18260/1-2--5431