Re: wave momentum

[James McLean <jmclean@CHEM.UCSD.EDU>]

Philip Zell wrote:
> Pressure, velocity, and temperature do change across a shock front.  I think a
> shock is, by definition, a discontinuity.  The changes are described by a set of
> "jump conditions" called the Rankine-Hugoniot equations.  Each equation can be
> expressed in terms of the adiabatic gas constant (gamma) and M1, the Mach number
> for the gas behind the shock front.
>
> Pressure:  P2 / P1 = 1 + [2*gamma*(M1^2 - 1) / (gamma + 1)]
>
> Density:   rho2 / rho1 = [1 + ((gamma + 1)/(gamma - 1))*P2/P1] / [((gamma + 1) /
> (gamma - 1)) + P2/P1]
>
> Temperature: T2 / T1 = (P2 / P1)[((gamma + 1)/(gamma - 1)) + (P2/P1)] / [1 +
> ((gamma + 1) / (gamma - 1))*P2/P1]

This is one of the great things about this list:  people with different
knowledge bases and viewpoints all adding to the mix.  I was actually
thinking of astrophysical shockwaves when I wrote my note a few cycles
back, but I had no idea about these quantities changing.

Would it be correct to view a sonic boom as a shock wave with Mach
number 1?  For that special case, I get the above ratios all coming out
to 1.

--
--James McLean
jmclean@chem.ucsd.edu
post doc
UC San Diego, Chemistry