Numerical Analysis of Combustor Flow Fields in Supersonic Flow Regime with Spalart-Allmaras and k-ε Turbulence Models

Abstract

In this numerical study, supersonic combustion of hydrogen has been presented for Mach 2. The combustor has a single fuel injection parallel to the main flow from the base. Finite rate chemistry model with k-e model and Spalart-Allmaras (S-A) Model have been used for modeling of supersonic combustion. The coupled phenomena of mixing and burning cm only be numerically modeled with the inclusion of a finite-rate chemical kinetic mechanism. The main issue in supersonic combustion is proper mixing within short burst of time. Attention is paid to the local intensity of heat release, which determines, together with the duct geometry, techniques for flame initiation and stabilization, injection techniques and quality of mixing the fuel with oxidizer, the gas-dynamic flow regime. The two-dimensional mathematical model involves the k-e and Spalarts-Allmaras turbulence model, modified for supersonic compressibility, and a detailed kinetic mechanism of mixture combustion. The five main parameters were considered like Mach number stagnation temperature, mass fraction, stagnation pressure and velocity. The result shows the better mixing of fuel and the flame speed increases almost linearly. The stagnation temperature in the combustion reaches up to 2820K. Fluctuation in pressure and Mach number was due to shock train. Supersonic combustion is the key enabling technology for sustained hypersonic flights. In scramjet engines of current interest, the combustor length is typically of the order of 1 m, and the residence time of the mixture is of the order of Milliseconds. Due to the high supersonic flow speed in the combustion chamber, problems arise in the mixing of the reactants, flame anchoring and stability and completion of combustion within the limited combustor length. The flow field in the scramjet combustor is highly complex. It is shown that when the flight speed is low, the kinetic energy of the air is not enough to be used for the optimal compression. Further compression by machines is needed in order to obtain a higher efficiency. For example, a turbojet employs a turbine machine for further compression. When the flight speed is higher than a certain value, the air flow entering a combustor will remain to be supersonic after the optimal compression. With a further compression (i. e. deceleration), the efficiency