Modelling of Supersonic Combustion using Finite-Rate Eddy-Dissipation (FRED) and Eddy-Dissipation Concept (EDC) Turbulence Chemistry Interaction (TCI) Models

This research focuses on supersonic combustion using Shock wave application theory, utilizing shock induced combustion with commercially available Ansys ® Fluent. The dominant mode employed with the design of scram jets is non-premixed fuel induction that entails complex geometries such as flame holders, cantilevered injectors etc. A premixed mode paired with shocked induced combustion, on the other hand, can be achieved with simpler geometries than other configurations. In current research work combustion as induced by a normal and oblique shock waves is investigated. Hydrogen gas at stoichiometric ratio and equivalence value was used as fuel. Normal shock induced combustion was investigated for flows accelerated in diverging test section at sea level conditions. Initially a non-reacting flow was studied. Subsequently, a case for reacting flow and supersonic combustion with normal-shock-induced ignition was investigated. For H2 combustion with NOx, a twenty-one (21) species variant was explored. The hydrogen combustion sub-mechanism was taken from Li et al. and comprises 21 elementary chemical steps. NOx sub-mechanism is based on the Glarborg group's research available with Fluent. A reaction zone was observed at Mach Line as well as radical formation zones were observed at two points beyond the Mach line. Hydrogen gas and Oxygen mass fraction was reduced across reaction zone whereas water formation was observed in the chamber. In the second case, the model is chosen from the experiment of Tan et al to model oblique shock induced combustion. A premixed air-hydrogen gas mixture at stoichiometric ratio is incident at Mach 5, hits a dual ramp configuration at varying incident angles. A global reaction mechanism is chosen for hydrogen gas combustion reaction along with FR/ED model for TCI in Ansys ® Fluent. Oblique shocks are created, and close coupling between the reaction zone and the shockwave occurs as a shock induced combustion, where burnt gases at elevated static pressure, density and temperature are observed post shock wave. The flow analysis for reacting flow shows a positive correlation between Mach numbers, flow turning angle and the heat of reaction. Whereas, there is a negative correlation between altitude and heat of reaction. Combustion is also modelled with Eddy Dissipation Concept (EDC) and it predicts a greater pressure ratio jump at shock wave formation. It also predicts more product formation compared to FR/EDM.