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i need some help on wind tunnels here. Basically i need to find out more on the operation principles behind wind tunnels.

Basically, wind tunnels provide simulation environment of high speed (transonic) flows by mimicking the reynolds number on the actual flow, because of dynamic similarity (i hope i got this right).

1. My question is, how exactly does wind tunnel achieves this reynolds number?

by looking at the equation: Re = (density*velocity*dimension)/dynamic viscosity.

so to achieve a desired reynolds number, or to attain a maximum possible reynolds number, we would only have to adjust the components that make up Re? eg: changing the medium of fluid flow? presurrizing the air to gain density?

2. The next question is about 'test rhombus'. Its been mention in many articles that a test rhombus is placed in the testing section of a wind tunnel to be tested for aerodynamic performance. Is this 'test rhombus' a generic term for arifoil sections that are to be tested? or its literally a double wedge (rhombus) airfoil?

also, is there a different 'test rhombus' for different wind tunnels?(low speed, transonic or supersonic,hypersonic)

thank you!

regards

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# Aerospace Wind Tunnels

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