Figure 5 - Cavitation in the Tip Vortices of a Model Propeller 



Finally, following an example given by Ackeret, 10 consider the con- 

 ditions in an unsteady flow. The contribution to the pressure due to a time 

 rate of change of a velocity potential <j> is 



P = P -"8t 



'41 



For a receding piston, in a tightly fitting cylinder, the velocity potential 

 is 



<t> = xu(t) 



where x is measured from the beginning of the motion. 

 Substituting this into [4], the pressure is 



P = p-p*t 



[5] 



