# How does one vary Mach number and dynamic pressure independently in a wind tunnel

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 August 3, 2009, 12:23 How does one vary Mach number and dynamic pressure independently in a wind tunnel #1 New Member   JaneD Join Date: Aug 2009 Posts: 1 Rep Power: 0 Hello all, I am newbie to fluid dynamics. How does one vary Mach number and dynamic pressure independently in a wind tunnel. i want to repeat the same in CFD. Thanks, Jane

August 3, 2009, 13:00
#2
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Brendan Sloan
Join Date: Mar 2009
Posts: 24
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Quote:
 Originally Posted by my_cfd Hello all, I am newbie to fluid dynamics. How does one vary Mach number and dynamic pressure independently in a wind tunnel. i want to repeat the same in CFD. Thanks, Jane
Pt/P = {1+ [((gamma-1)/2)*Mach^2]} ^(gamma/[gammma-1])

Pt = Total pressure
P = Static pressure
gamma = ratio of specific heats (1.4 for air)
Mach = Mach number

Change your static pressure, and you can adjust your total pressure & mach number semi-independantly of each other.

If your doing this in a wind-tunnel, you obviously need a pressurised tunnel.

Beware of Reynolds effects while doing this however. Matching compressibility effects with Reynolds effects on a scaled tunnel model is not possible*.

*at least, not that I'm aware.

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