631 



"The Relation Between the Appearance oi"" the Plumes ana 

 the Gas Globe Behavior in Underwater Explosions" * 



G . K . Hartmann 

 U. S. Naval Ordnance Laboratory 



The appearance of the vjater surface above an underwater 

 explosion changes after tiie explosion in what seems to be an 

 irregular fashion as time goes on. Although the initial 

 velocity of the water surface and the resultant shape of the 

 dome in its early stages are extremely reproducible, the later 

 stages of the water motion seem to occur in a random manner. 

 The purpose of this note is to show that the later appearance 

 of the surface and in particular the rather arbitrary behavior 

 of the plumes are related in a fairly quantitative way to the 

 oscillation and migration of the gas globe. The period of 

 oscillation and the amount of migration are of course deter- 

 mined by the weight of charge of a given kind and by the depth 

 of the charge . 



The phenomena under consideration will now be described 

 in more detail . 



Observation of the water surface reveals that for an ex- 

 plosion at a moderate depth, say 300 lbs. at 30 ft., the water 

 is broken into white spray over a delimited area (outside of 

 which there is a distinctly dark region) and that this spray 

 moves upward vertically with greatest velocity over the charge 

 and decreasing velocities at greater distances. This spray 

 dome, which can be shown to be caused by the reflection of the 

 shock wave at the free surface, is actually freely falling 

 water and moves upward under the influence of gravity and air 

 drag until it reaches its maximum central height whereupon it 

 falls bacK into the surface, continuously changing its shape as 

 it does so. At some stage in this process other fingers or 

 jets of spray and often explosion gases, identified by their 

 carbon black, break through the dome with various velocities. 

 Sometimes these plumes appear traveling radially from some point 

 near the surface and sometimes they are limited to single high 

 speed vertical jets. The character of these plumes and the 

 times at which they appear are related to the oscillation and 

 migration of the explosion gas globe. 



* This note is taken from material presented by the author at 

 the Washington meeting of the American Physical Society In the 

 spring of 19^7- 



