What is the giveaway that region 4 is Rayleigh flow?

[FannoFlow88]

Homework Statement

What is the giveaway the region 4 is rayleigh flow

Relevant Equations

from given question i can see there is an oblique shock then normal shock then isentropic expansion. what follows is rayleigh flow. what tells me that from question attached

answering part c

could someone explain each region of diagram. thanks. I've got parts a and b correct

 

[Lnewqban]

Homework Statement:: What is the giveaway the region 4 is rayleigh flow
Relevant Equations:: from given question i can see there is an oblique shock then normal shock then isentropic expansion. what follows is rayleigh flow. what tells me that from question attached

According to these links, the lack of friction and the heat from combustion in region 4 should be the giveaway:

https://en.wikipedia.org/wiki/Rayleigh_flow

"Rayleigh flow refers to frictionless, non-adiabatic flow through a constant area duct where the effect of heat addition or rejection is considered."

https://en.wikipedia.org/wiki/Fanno_flow

"Fanno flow is the adiabatic flow through a constant area duct where the effect of friction is considered."