As I understand it, the local speed of sound is defind by:
a = sqrt(gRT/M)
Where:
g(Gamma on a UK keyboard!) = Ratio of specific heats, also known as the adiabatic constant
R = Universal Gas Constant
T = Absolute Temperature
M = Molecular mass of gas
Certainly R and M are independant of pressure. I thought g (Gamma) was as well. If that's the case, the the local speed of sound, and therefore Mach No, are only affected by temperature.
I guess that if pressure does have an effect, it must be that gamma varies with pressure...
Looks like I've just managed to repeat dexter
