Ideas for high school wind tunnel?

[mishima]

TL;DR Summary

Looking for some new directions I can take the class using physical wind tunnel

Hi, I teach a high school Aerospace Engineering course. We have a small wind tunnel that can reach about 85 mph, and test objects roughly the size of a 3x5 notecard. It has a pitot tube and force scale.

In the past we have constructed airfoils using their 4 or 5 digit NACA codes, then tested them in the tunnel (cut foam and 3d printed foils). We then compare the experimental data with a NASA simulator for the same airfoil. Typically the L/D ratio is pretty close, and we can then discuss how scaling is related to Reynold's number.

Sometimes it seems anti-climatic, and that we don't get anything that interesting from testing them in a wind tunnel. I was looking for fresh ideas, new ways to make an activity that could be fun and memorable for kids.

I never had a college course with a wind tunnel, so perhaps I could hear from some AE majors about what college wind tunnel activities have really stuck in mind, then find a way to scale it down to high school level.

 

[Flyboy]

For high school level, you could do other types of shapes. Cars, semi trucks, etc, stuff that’s more approachable from an everyday standpoint, at least for starters and to help them get familiar with the wind tunnel.

Another option would be to add things like flaps or slats (fixed or adjustable outside the tunnel is the most likely way to do it given space constraints) to demonstrate how they impact low-speed performance. Basically, you could do a comparison with the “clean” and “dirty” versions of an airfoil.

 

[berkeman]

Yeah, but I think the small test volume is his biggest limitation right now (3"x5"x?")

 

[mishima]

The entire enclosed test space size is about 5x5x15. The wing sections we test are 3x5, spanning almost the full width.

Jetstream 500 Product Page

 

[FactChecker]

Can you 3D print or buy some small model airplanes?

 

[berkeman]

The entire enclosed test space size is about 5x5x15. The wing sections we test are 3x5, spanning almost the full width.

Jetstream 500 Product Page

Wait, what units? I'd assumed inches, but should it be feet, meters, light-years...?

 

[Flyboy]

Wait, what units? I'd assumed inches, but should it be feet, meters, light-years...?

“The Jet Stream 500 is a low cost desktop wind tunnel with a 5 1/4" square 16" deep test area.”

Plenty of space for some more complex models, so long as you keep the scaling in mind.

 

[Klystron]

NASA wind tunnels include a variety of stress and strain gauges inside (semi-) permanent aerodynamic mounts used to secure test models. This mount also serves as the conduit for pitot pressure tubes and embedded electronics from the model to your data collection center.

Given the limited space of the wind tunnel, consider fabricating a minature mount that extends normal to the 'floor' of the tunnel. Run several calibrations without attached models. Invert the mount from 'floor' to 'ceiling' and recalibrate the tunnel. How have the data readings changed?

Train student operators to observe important fluid values and how they vary from startup through shutdown then compare their observations to collected data. Near- and realtime graphs displayed on smartphones and laptops of data collected from the various gauges immerse the students in the aerodynamics of the wind tunnel itself, even before adding models. Monitor local weather conditions such as pressure and temperature and compare to readings inside the tunnel.

Consider developing standard identification numbers for each run of experiements with mandatory before and after calibration runs of the wind tunnel. Assign students definitive roles such as chief engineer, model specialists, software or data engineers, and wind tunnel operators. Develop checklists for each participant to follow. Rotate roles during the semester.

After many runs, attention shifts from the wind tunnel and model to observing computational fluid dynamics (CFD) numbers change on the neartime screens in relation to fluid movement inside the test chamber. Emphasize safety and procedure.

 

[berkeman]

Does your tunnel have provision for moving streamlines around?

 

[mishima]

Does your tunnel have provision for moving streamlines around?

That's one thing I'd definitely like to explore more. I haven't used dry ice or a (glycerin) fog machine to get those kinds of laminar visuals before. I was worried about the glycerin fog crudding up the wind tunnel prop, and never really researched how those effects are otherwise created.

It does have an adjustable angle of attack knob from outside while the stream is flowing, from -30 to +30 in increments of 5 degrees.

 

[Klystron]

As a high school teacher, wind tunnel experiments involve relations among a variety of departments. Physics and mathematics for experiment design and computations. Electronics for sensors, wiring and wind tunnel controls. Various 'shop' stewards for onsite fabrication and support. Aero and automotive clubs for model development. Defintely computer science for software, CFD and data collection. Depending on how your school creates budgets, wind tunnel costs might be spread across several accounts.

Consider planning and announcing wind tunnel exhibition runs on special event days that include STEM and nontechnical students, administrators, parents and visitors. Have leading students explain how studying Reynolds number and similar computed values lead to improved flight and automotive safety.

 

[boneh3ad]

I am hereby seconding the smoke vis idea above. Using a fog machine or similar shouldn't cause you any problems. It's a very common technique in wind tunnels. Other flow visualization options should definitely be considered. It's one thing to measure forces and moments. It's another thing to connect the answers you get out of those measurements to flow phenomenology (like separation/stall).

 

[mishima]

Could it be as simple as drilling some holes in a piece of PVC then feeding the fog through to get good lines? As long as the PVC is capped, the pressure should be the same at each hole.

 

[Flyboy]

Other option, since you have access to a 3d printer, is to make the smoke delivery as streamlined as possible to minimize disturbance. Might be a fun project/competition for the students, actually.

 

[mishima]

Thanks, that's a great idea, I'll have them investigating printer settings and print orientation to give the best streamlines. They can design different methods to attach the 'seeding rake' to the wind tunnel's inlet, and try different rake spacings.