Drag Coefficient Estimates Using a Smoke Wind Tunnel

James King, Indiana University-Bloomington
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This lab exercise utilizes a small (and relatively easy to make) wind tunnel with a fog tracer that helps students visualize the flow dynamics around obstacles. In this exercise the use of cylinders perpendicular to the flow allows for estimations of drag coefficients and visualization of different Reynolds number flow patterns. Wind tunnel instructions are included.

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Although the exercise is for a junior/senior level course in sedimentary processes/sedimentology, the tunnel can be utilized for demonstrations at all levels. The exercise is a 3 hour laboratory given after Reynolds number context has been given in the lecture.

Skills and concepts that students must have mastered

A strong background in hypothesis testing in a lab environment, good knowledge of fluid flow interactions and critical thinking skills.

How the activity is situated in the course

The activity is one of six lab exercises in the course.


Content/concepts goals for this activity

An understanding of Reynolds number similarity through the testing of various speeds and diameter cylinders.

Higher order thinking skills goals for this activity

Experimental design, synthesis of observations/interpretations with theory and some creative thinking to get the fog to work properly.

Other skills goals for this activity

Description and Teaching Materials

Flow visualization with a fog wind tunnel (Acrobat (PDF) 339kB Jun9 14)

Fog wind tunnel schematic (Acrobat (PDF) 40kB Jun9 14)

Teaching Notes and Tips

Make sure that the tunnel has been approved to be used in the classroom or use it outside. The fogger requires some warm-up time and needs to be at the highest/hottest setting for the tracers to be seen (it will also help to have the back wall of the tunnel a dark color). The normal liquid for the fogger can be used (as it will be exhausted through a fume hood), but distilled water and glycerin will also work just as well.


The exercise is to be completed individually and submitted within a week of the experiments. The use of other peer-reviewed literature to substantiate the results is encouraged, while comparisons with other published data complemented with a detailed discussion would be in fulfillment of the learning goals.

References and Resources

Middleton, G.V., and J.B. Southard, 1984. Mechanics of sediment movement. Tulsa, OK. Society of Economic Paleontologists and Mineralogists. 401 pp.