Rayleigh flow refers to diabatic flow through a constant area duct where the effect of heat addition or rejection is considered. Compressibility effects often come into consideration, although the Rayleigh flow model certainly also applies to incompressible flow. For this model, the duct area remains constant and no mass is added within the duct. Therefore, unlike Fanno flow, the stagnation temperature is a variable. The heat addition causes a decrease in stagnation pressure, which is known as the Rayleigh effect and is critical in the design of combustion systems. Heat addition will cause both supersonic and subsonic Mach numbers to approach Mach 1, resulting in choked flow. Conversely, heat rejection decreases a subsonic Mach number and increases a supersonic Mach number along the duct. It can be shown that for calorically perfect flows the maximum entropy occurs at M = 1. Rayleigh flow is named after John Strutt, 3rd Baron Rayleigh.
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Some articles on rayleigh flow:
... The Rayleigh flow model has many analytical uses, most notably involving aircraft engines ... These properties make the Rayleigh flow model applicable for heat addition to the flow through combustion, assuming the heat addition does not result in dissociation of the air-fuel mixture ... of an engine due to thermal choking is very undesirable due to the decrease in mass flow rate and thrust ...
... The Fanno flow model is often used in the design and analysis of nozzles ... the converging or diverging area is modeled with isentropic flow, while the constant area section afterwards is modeled with Fanno flow ... the nozzle throat, where M = 1 if the flow is choked ...
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