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If I want to know how my aircraft component performs in different atmospheric conditions, I might want to test it in a wind tunnel. What sorts of weather conditions have been tested in a tunnel?

I am thinking about 1 m scale wind tunnels or bigger, not tiny ones.

I saw Boeing offers an icing tunnel. I found some very old specifications (p. 6). It does not say if the humidity can be controlled. The temperature range -25° to 50°F does not cover the heat aircraft often encounter. Are there other capabilities?

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    $\begingroup$ NASA Glenn has tunnels with a very wide range of performance. Here are some impressive specs to take a look at: www1.grc.nasa.gov/facilities/irt www1.grc.nasa.gov/facilities/10x10 $\endgroup$
    – Adam
    Sep 23, 2023 at 18:15
  • $\begingroup$ Note: do not overestimate wind tunnels. Computer simulation, and then real tests are the most important parts. Wind tunnels cannot provide accurate results if you do not use a full scale model (and you can build a model and attach it to a real aircraft to validate all weather conditions). $\endgroup$ Sep 25, 2023 at 7:31

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Yes, icing tunnels can run at very cold temperatures and can introduce water vapor in quantities sufficient to represent humidity, clouds, and precipitation.

Wind tunnels often control pressure and temperature of the flow. The first pressure tunnels provided the first chance to understand the effect of Reynolds number on airfoils.

Wind tunnels are usually cooled (rather than heated) -- the temperature in a closed circuit wind tunnel will rise to very hot temperatures if it is not cooled (or shut down to cool). Closed circuit tunnels also often exchange a fraction of the air on each circuit to reduce the cooling requirements.

Some wind tunnels run gas other than air. Sometimes this is as simple as Nitrogen - which is basically air, but high speed tunnels sometimes run Helium, Argon, CO2, and other gasses.

Instead of running at high pressure, wind tunnels for testing engines often run at very low pressure (and temperatures). This way, they can simulate conditions for the engine operating at high altitude.

These tunnels aren't necessarily trying to model 'weather', but they are trying to represent the ambient conditions important to the system being studied.

For example, a spacecraft re-entering the edge of the atmosphere experiences an ambient condition of rarefied gas (where the air is so thin, the continuum assumption falls apart) at about Mach 26. By the time the spacecraft reaches the earth's surface, it will have experienced everything down to incompressible Mach zero flow at sea level.

At times during that re-entry, the flow will be so hot, the gas will convert to a charged plasma that interferes with radio communication.

No single wind tunnel can duplicate all of these conditions, but there are wind tunnels and other related ground test equipment to simulate each of these phenomena that are used in the development of spacecraft and aircraft.

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  • $\begingroup$ "Wind tunnels are usually cooled (rather than heated) -- the temperature in a closed circuit wind tunnel will rise to very hot temperatures if it is not cooled" Where did you get this information? $\endgroup$ Sep 23, 2023 at 1:40
  • $\begingroup$ Think about the control volume of a moderate closed circuit wind tunnel. Suppose it has a 100 Hp motor driving the fan. Since the flow can not accelerate to infinite speed (due to friction), that is 100 Hp of work that eventually turns into heat. You're putting lots of work in, but aren't taking any heat out. I have been in several wind tunnels with cooling apparatus. grc.nasa.gov/www/k-12/airplane/tuncret.html "Hotter running conditions than an open return tunnel. Tunnel may have to employ heat exchangers or active cooling." $\endgroup$ Sep 23, 2023 at 4:50
  • $\begingroup$ Good information. The difference between active and passive cooling is huge - which is it in practice? $\endgroup$ Sep 23, 2023 at 12:07
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    $\begingroup$ There are closed circuit tunnels with at least four (and combinations of the four) approaches -- do nothing, simply limit run times. Exchange some fraction of air with cool ambient air (not a fully closed return). Use various approaches to passive cooling. Use elaborate heat exchangers with cooling towers to actively cool. Most large wind tunnels are one-off designs tailored to the targeted flow conditions, the site, and the cost of materials and labor at the time of construction. In practice, it is an OR -- not a single answer. $\endgroup$ Sep 23, 2023 at 20:33

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