Under water explosion

This case is a 2D Cartesian test. The square domain is composed of air (blue), water (orange) and air cavity (red) as represented in Fig. 66. This test is referenced in ./libTests/referenceTestCases/NEqDEM/2D/underWaterExplosion/. The corresponding uncommented line in ECOGEN.xml is:

<testCase>./libTests/referenceTestCases/NEqDEM/2D/underWaterExplosion/</testCase>

Fig. 66 Representation of density mixture initial conditions for 2D under water explosion.

\[ \begin{array}{|c|c|c|c|} \hline & \text{Water} & \text{Air} & \text{Air cavity} \\ \hline \rho \, [\text{kg/m}^3] & 1000 & 1.225 & 1250 \\ \hline u \, [\text{m/s}] & 0 & 0 & 0 \\ \hline P \, [\text{Pa}] & 1.01325 \times 10^{5} & 1.01325 \times 10^{5} & 10^{9} \\ \hline \end{array} \] Initial conditions for 2D under water explosion.

The initial characteristics of the run are:

\begin{array}{|l|l|} \hline \textbf{Characteristic} & \textbf{Value} \\ \hline \text{dimension } \mathrm{[m]} & 4 \times 3 \\ \text{mesh size} & 100 \times 75 \\ \text{boundary conditions} & \text{non-reflecting} \\ \text{final solution time} & 2 \times 10^{-3} \ \mathrm{s} \\ \text{solution printing frequency} & 1 \times 10^{-4} \ \mathrm{s} \\ \text{precision} & \text{1st order} \\ \hline \end{array}

Results are shown in Fig. 67. Initially, the air cavity is at high pressure. When the interface between the air cavity and the water disapears, a shock wave propagates in the water and the air-cavity region relaxes. Part of this shock wave is transmitted in to the air region above. With the help of the density evolution, shown through a Schlieren visualization, we can observe a kind of explosion between the water and the air regions.

Fig. 67 Schlieren visualization and volume fraction of under water explosion.