Numerical studies and validation of combustor and annular isolator interactions of hydrocarbon based axisymmetric dual combustion ramjet

Abstract

Combustor Intake interactions study is very important for design of Ramjet/Scramjet propulsion systems. High Combustion-induced back pressures make the shock train propagate upstream further and interfere the flow of inlet and the scramjet would unstart. The study has more relevance especially for the propulsion systems like Dual Combustion Ramjet (DCR) due to its wider range operation of Mach number. In this paper, numerical simulation of flow field in an axisymmetric scramjet/ramjet combustor with annular isolator is carried out. Configuration chosen for simulation is Dual Combustion Ramjet, which has a dump subsonic combustor, main supersonic Combustor and an annular isolator. Objective of the work is to evolve a CFD procedure for combustor-isolator interaction and validation of the model with experimental data. Geometry of model DCR is taken from literature for simulations and studies are carried out for Isolator inlet Mach No. 1.79 and 2.23. Favre Averaged equations are solved using Commercial code–ANSYS FLUENT. Premixed composition of air and Kerosene is introduced into dump combustor. Reactive flow is modelled using 7 species and 4 step chemistry. Numerical simulations have been carried out with various turbulence models namely k–ε (Standard), (RNG) k–ε, kω-Standard, kω-SST and combustor wall pressures were compared with experimental results. Error in estimation of starting location of Shock train, Maximum Pressure, Average pressure in combustor is compared. (RNG) k–ε predicted shock train location with an error difference of 5% compared to k–ε (Standard). Further, effect on shock train position in isolator with change in gas generator equivalence ratio is also studied for free stream Mach numbers 4 and 5. Shock train moves upstream in Isolator with increase in gas generator equivalence ratio. Various parameters such as Wall static Pressure, Shock train location, length and static pressure along shock train centre, Velocity profile and Combustion efficiency are compared for reactive flow turbulence models.