PAPI 32
29th Apr 2010, 20:21
Could someone explain to me how with an oblique shock wave what happens to the local speed of sound in front of an oblique shock wave and behind it, along with the mach number.
Does it behave in the same way as a normal shock wave?
Keith.Williams.
29th Apr 2010, 20:43
A shock wave is an instantaneous increase in static pressure.
When air flows through a shock wave it is suddenly compressed so that its static pressure becomes equal to the static pressure behind the shockwave.
This sudden compression of the air causes the following.
Static pressure increases.
Density increases.
Velocity decreases.
The increased temperature causes the local speed of sound to increase.
The reduced velocity and the increased local speed of sound cause the Mach number ot decrease.
Because the compression is very sudden, some of the pressure energy is converted into heat, so the total pressure decreases.
The only difference between the effects of a normal shockwave (which is at 90 degrees to the flow) and an oblique shockwave (which is at a lesser angle to it) is that the changes through a normal shock wave are much more severe.
You could say that because the air passes through an oblique shock wave at an angle, the effects are less abrupt.
The principal effect of this difference is that when air flows through a normal shckwave its mach number always reduces to less than Mach 1.
In order to form an oblique shock wave the incoming air mach number must be more than mach 1. When air flows through an oblique shock wave its mach number reduces, but is still more than mach 1.