Figure 13. Water Column of an Explosion with Venting Bubble. Charge: 2.75 lbs TNT and 3 grams 

 KC10,/A1 50/50. Depth: 0.4 maximum bubble radii. 



blow-out in this case. The small scale test shown on the right hand side concerns the 

 same conditions as shown by the larger explosion on the left. The water surface is 

 at the little triangle. The black lines are steel bars which support the windows of the 

 tank. In this model test an explosive is used which yields highly luminous products. 

 This makes it possible to study the motion of the gas. No blow-out is visible here. 

 On the contrary, there are indications that air is sucked into the bubble, because, 

 after reaching its maximum, the bubble does not contract again. Hence the pressure 

 inside the bubble must have been in equilibrium with the ambient pressure. This 

 venting of the bubble occurs through the column and probably causes the contraction 

 near the base. 



The Case of the Non-Venting Bubble 



If the depth of explosion is increased further, the appearance of the water 

 column is radically changed, Fig. 14. A thin water jet shoots upward which is sur- 

 rounded at the base by a lower and broader spray formation. The bubble does not 

 vent in this case. The first frame of the model test which scales the same test geometry 

 shows the bubble shortly after the maximum in the stage of contraction. There is 

 clear water above the bubble which proves that there was no communication between 

 the bubble and the atmosphere. 



The model test in Fig. 14 scales a small charge weight (1 gram). Consequently, 

 the effect of gravity is small and the above mentioned repulsion of the pulsating 

 bubble from the water surface becomes dominant: Frames 2 and 3 show that the 

 bubble migrates downward. 



339 



