Foa 



i^V\\\\'^\\VVV\\\\\V\VV\\N\\\\\\\'\V\VVVV'^'v'v^'^ ' ^^ I 



(a) 



Fig. 3 - Plane -flow cryptosteady 

 pressure exchange 



frame, to common orientations at their interfaces. If the primary stream spans 

 the whole width of the interaction space (as in the situation of Fig. 3), the entire 

 flow is deflected in pressure exchange to a common orientation in the relative 

 frame. Under these conditions, and if the mutual deflection is assumed to be 

 completed before any appreciable mixing takes place across the interfaces, the 

 process can be analyzed in the relative frame as an interaction between steady 

 isoenergetic flows. The resulting modification of the flow is described by the 

 velocity vector diagram of Fig. 4 for a situation in which the final pressure pj 

 is equal to the static pressure Po of the undisturbed secondary flow. The ve- 

 locities of the deflected flows in the relative frame are 7^ and ~c^, and the 

 corresponding "absolute" velocities are u^^ and U^^. It can be seen, from the 

 relative magnitudes of these vectors at the beginning and at the end of the inter- 

 action, that in this process the secondary flow gains mechanical energy, in the 

 absolute frame, at the expense of the primary flow. 



The "deflection phase" just described is normally followed by further inter- 

 actions. A second phase of pressure exchange takes place if the two flows, fol- 

 lowing the deflection phase, are subjected together to Coriolis or other acceler- 

 ations normal to their interfaces, as in a rotating flow field or in a passage of 

 varying cross section. Heat transfer and mixing also start as soon as the two 



1356 



