Faculty Resource Center

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Overview

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Principles of Measuring Turbulent Flows

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Protocol

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Analysis and Results

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Applications

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Summary

# Measuring Turbulent Flows

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI

Turbulent flows exhibit very high frequency fluctuations that require instruments with high time-resolution for their appropriate characterization. Hot-wire anemometers have a short enough time-response to fulfill this requirement. The purpose of this experiment is to demonstrate the use of hot-wire anemometry to characterize a turbulent jet.

In this experiment, a previously calibrated hot-wire probe will be used to obtain velocity measurements at different positions within the jet. Finally, we will demonstrate a basic statistical analysis of the data to characterize the turbulent field.

1. Measure the width of the slit, W, and record this value in table 1.
2. Set the hot-wire anemometer at a distance from the exit equal to x = 1.5W along the centerline. Record this streamwise position in table 2. The centerline is the origin of the spanwise coordinate (y = 0).
3. Start the data acquisition program for traversing the jet. Set the sample rate at 500 Hz for a total of 5000 samples (i.e. 10s of data).
4. Record the current spanwise position of the hot-wire in table 3.

Figure 5 shows the distribution of average velocity across the jet at the downstream position x = 3W. And Figure 6 shows the distribution of turbulence intensity across the jet at the same downstream position. Table 3 has the results for the local values of average velocity and turbulence intensity at the streamwise position x = 3W. The last column of this table is the ratio between the local v

This experiment demonstrated the application of hot-wire anemometry for characterizing turbulent flows. Given that turbulence exhibits high frequency velocity fluctuations, hot-wire anemometers are suitable instruments for its characterization due to their high time-resolution. With this in mind, we used a calibrated hot-wire anemometer to characterize the average local velocity and turbulence intensity at different positions within a planar jet. These quantities were determined using statistical descriptors for turbulen

1. Chapra, S.C. and R.P. Canale. Numerical methods for engineers. Vol. 2. New York: McGraw-Hill, 1998.
2. King, L.V. On the convection of heat from small cylinders in a stream of fluid: determination of the convection constants of small platinum wires with applications to hot-wire anemometry. Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character 214 (1914): 373-432.
3. White, F. M. Fluid Mechanics, 7th ed., McGraw-Hill, 2009.
4. Munson, B.R., D.F. Young, T.H. Okiishi. Fundamentals of Fluid Mechanics. 5th ed., Wiley, 2006.
5. Buckingham, E. Note on contraction coefficients of jets of gas. Journal of Research,6:765-775, 1931.

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