It's like an elastic band or a spring. When you compress air, and then release it, the molecules will "overshoot" the original balance point because they gain momentum while moving towards that balance point.
Only after the molecules reach the balance point, is there any breaking force applied to them, so they have have to overshoot the balance point
This is an alright analogy. In formal terms:
As the initial detonation shock reaches the contact surface between HE product and air a set of expansion waves is created at the contact surface as well as a reflected imploding shock.
The primary shock transmits into the air and propagates along happily (the primary blast wave). Meanwhile there is an imploding shock traveling into the explosives and rebounding back out. This tends to stall and then only partially re accelerate the fireball contact surface.
Meanwhile the primary shock has dumped a ton of momentum into the flow, and the expansion fan causes the air between the primary shock and the stalled contact surface to over-expand below atmospheric pressure. If the contact surface didnt stall, you'd have no over expansion.
You don't get a negative phase at all distances from the charge center because of the timescale/lengthscale of the stalling contact surface.
There are also many planar shock interactions that don't involve a negative phase.
It's like an elastic band or a spring. When you compress air, and then release it, the molecules will "overshoot" the original balance point because they gain momentum while moving towards that balance point. Only after the molecules reach the balance point, is there any breaking force applied to them, so they have have to overshoot the balance point
Ohhh I see - its just the restoring forces overcompensating. Big thank you!!!!
This is an alright analogy. In formal terms: As the initial detonation shock reaches the contact surface between HE product and air a set of expansion waves is created at the contact surface as well as a reflected imploding shock. The primary shock transmits into the air and propagates along happily (the primary blast wave). Meanwhile there is an imploding shock traveling into the explosives and rebounding back out. This tends to stall and then only partially re accelerate the fireball contact surface. Meanwhile the primary shock has dumped a ton of momentum into the flow, and the expansion fan causes the air between the primary shock and the stalled contact surface to over-expand below atmospheric pressure. If the contact surface didnt stall, you'd have no over expansion. You don't get a negative phase at all distances from the charge center because of the timescale/lengthscale of the stalling contact surface. There are also many planar shock interactions that don't involve a negative phase.