Hydrocodes » High Explosive Blast
Hydrodynamics of High Explosive Blast
Before considering any interaction with structures it is important to assess the basic 
A shock wave is generated in the air. This slows down as it expands and weakens. We can plot the time history of the pressure generated by this blast. In the movie this is shown at 1m.
As well as the shock the fireball expands but eventually reaches a maximum radius and oscillates about this. This is the contact surface shown in the movie.
A second shock also forms inside the fireball. This starts off by propagating inwards but reflects at the centre and produces a second , weaker outward going shock wave. This is seen on the time history plot as a second smaller peak. This has important effects in coupling to structures or buildings.
The movie also shows how the pressure and internal energy vary radially outward from the detonation as time progresses.
In reality the fireball surface is turbulent. In the next movie we see how this develops. We make use of symmetry and only show a quadrant of a sphere.
The importance of the turbulence is when we need to consider late time combustion of the explosion products as they mix with air. Some explosives have a significant energy release in this phase. This is important for explosions inside buildings where this late time energy gives a significant pressure rise in a closed volume. The next movie repeats the previous calculation but with secondary burn enabled.
Finally in this series we show that the effect of a wall changes the behaviour dramatically, not only in terms of the shape but also in the turbulent behaviour late on.