F,21 • HEAT TRANSFER IN ROCKET MOTORS 



It is to be emphasized that the strong tendency for stabiHzation exhibited 

 in Fig. F,20h is caused by the transient heat lag of the skin and not by 

 radiation, since radiation was almost negligible compared to the heat 

 absorption of the skin. Thus, transient firings of the above type are of 

 great importance in the study of boundary layer characteristics at super- 

 sonic speeds. However, steady state temperature data, when available, 

 will check radiation rates of cooling and their effect on boundary layer 

 stability. Reliable data at hypersonic speeds and higher altitudes will be 

 useful for studying the effect of slip flow on heat transfer. It is of interest 

 to note in Fig. F,201 that after 70 sec of flight the flow for the one-foot 

 station of the above-discussed V-2 had already entered the slip-flow 

 regime defined by Tsien [66\. 



234 56 789 



Log RCe 



Fig. F,201. Flow domain during flight of V-2 rocket no. 27 for 1 ft station. 



F,21. Heat Transfer in Rocket Motors. Another important heat 

 transfer problem is that of the rocket motor in which the metallic walls 

 must be protected against the high temperatures of the propellant gases. 

 The problem is essentially the same as in the aerodynamic heating of 

 high speed vehicles, except that in rocket motors the flow properties 

 change much more rapidly. The ambient temperatures in the nozzle 

 are always high, so that the nozzle wall, particularly at the throat, 

 must be continually protected by either regenerative or film cooling. 

 Only at hypersonic speeds does the boundary layer temperature on the 

 outside of a vehicle become comparable to that in the nozzle. Regener- 

 ative cooling is brought about by circulating some of the fuel in the motor 

 jacket before injecting it into the combustion chamber. Film cooling is a 



( 415 ) 



