  Thermal choking in combustor ducts is a matter of great interest to
researchers involved in the design and analysis of combustors. In case of
scramjet combustors, a thermally choked state is undesirable whereas for a
dual-mode combustor in the ram mode it is essential. Since real-life combustors
feature volume heat addition due to combustion, area variation, wall heat loss
and frictional losses, all of these effects must be included in the analysis.
The standard Rayleigh flow assumes a constant-area duct with no frictional
effects and a single heat addition/loss term without distinguishing between
combustion and wall heat transfer effects. Instead, a generalized Rayleigh flow
analysis is employed here which can account for all the above effects and also
provide for different fuel injection rates and mixing efficiency. The forward
and inverse heat transfer problems are stated and solutions are compared
between Rayleigh flow in constant-area and variable-area ducts. The analysis is
checked against a scramjet combustor in the literature and then used to study
the occurrence of thermal choking in a dual-mode combustor geometry. The
possibility of thermal choking and the location of the choking event can be
easily detected by this method. The shift in the thermal choking location with
variation in the duct heat and mass transfer state can be easily evaluated. In
this manner, the present method provides a quick and accurate tool for
preliminary design and analysis of ramjet and scramjet combustors.
