Computational fluid dynamics analysis of spray and combustion characteristics of a combustion chamber with prefilming air-blast atomizer

In this study, two-phase reacting flow through a combustion chamber with a prefilming air-blast atomizer is analyzed using Computational Fluid Dynamics (CFD). The combustion chamber analyzed belongs to a small scale turbojet engine that will be used in unmanned aerial vehicles. According to predetermined design criteria, the geometry of the combustion chamber is formed by means of one dimensional design methodologies and isothermal CFD simulations. The characteristics of the spray generated by the airblast injector are investigated with the two phase non-reacting CFD simulations of the flow through the atomizer. Droplet size and velocity distributions obtained from the spray analysis are used as boundary conditions in the reacting simulations. Realizable k-? turbulence model is used for turbulent flow coupled with the Hybrid Eddy Break Up combustion model for reactions. CFD simulations of Flame D of Sandia Laboratories have been performed in order to validate these models and the code, Star-CCM+. In addition, the flow of the dispersed phase is computed with Lagrangian models. In the spray analysis, primary breakup at the exit of the simplex nozzle, film formation due to impingement of droplets to the atomizer wall, film breakup arising from wave instabilities in the wall film and secondary breakup of fuel droplets are modeled. It has been observed that, the airblast atomizer generates a spray with a 20 ?m mean diameter and 15 m/s axial velocity. Moreover, in the reacting simulations, temperature and equivalence ratio distributions inside the combustion chamber have been predicted. As a result, combustion efficiency, RTDF, OTDF and pressure drop values are found as %97.4, %16, %28 and %4.9 respectively.