Thermodynamics

Chapter 17 | 843P 0V i ≅ 0ThroatP eP bxP bFIGURE 17–27P 0PP*Ma0Inlet10InletSonic flowat throatSonic flowat throatThroatThroatShockin nozzleShockin nozzleE, F, GABCDE, F, GExitDCBAExitP AP BP CP DP EP FP G}}}}}}Subsonic flowat nozzle exit(no shock)Subsonic flowat nozzle exit(shock in nozzle)Supersonic flowat nozzle exit(no shock in nozzle)xSupersonic flowat nozzle exit(no shock in nozzle)Subsonic flowat nozzle exit(shock in nozzle)Subsonic flowat nozzle exit(no shock)xThe effects of back pressure on theflow through a converging–divergingnozzle.mass flow rate through the nozzle. However, it does influence the characterof the flow in the diverging section.3. When P C P b P E , the fluid that achieved a sonic velocity at thethroat continues accelerating to supersonic velocities in the divergingsection as the pressure decreases. This acceleration comes to a suddenstop, however, as a normal shock develops at a section between thethroat and the exit plane, which causes a sudden drop in velocity to subsoniclevels and a sudden increase in pressure. The fluid then continuesto decelerate further in the remaining part of the converging–divergingnozzle. Flow through the shock is highly irreversible, and thus it cannotbe approximated as isentropic. The normal shock moves downstreamaway from the throat as P b is decreased, and it approaches the nozzleexit plane as P b approaches P E .When P b P E , the normal shock forms at the exit plane of the nozzle.The flow is supersonic through the entire diverging section in thiscase, and it can be approximated as isentropic. However, the fluidvelocity drops to subsonic levels just before leaving the nozzle as it