Numerical Study of Non-Reacting and Reacting Flow Characteristics in a Lean Direct Injection Combustor

Abstract

The Lean Direct Injection (LDI) combustion concept has been of active interest due to its potential for low emissions under a wide range of operational conditions. This might allow the LDI concept to become the next generation gas-turbine combustion scheme for aviation engines. Nevertheless, the underlying unsteady phenomena, which are responsible for low emissions, have not been widely investigated. This paper reports a numerical study on the characteristics of the non-reacting and reacting flow field in a single-element LDI combustor. The solution for the non-reacting flow captures the essential aerodynamic flow characteristics of the LDI combustor, such as the reverse flow regions and the complex swirling flow structures inside the swirlers and in the neighborhood of the combustion chamber inlet, with reasonable accuracy. A spray model is introduced to simulate the reacting flow field. The reaction of the spray greatly influences the gas-phase velocity distribution. The heat release effect due to combustion results in a significantly stronger and compact reverse flow zone as compared to that of the non-reacting case. The inflow spray is specified by the Kelvin-Helmholtz breakup model, which is implemented in the Reynolds-Averaged Navier Stokes (RANS) code. The results show a strong influence of the high swirling flow field on liquid droplet breakup and flow mixing process, which in turn could explain the low-emission behavior of the LDI combustion concept.

LES predictions of confinement effect on swirling flow generated by single helical axial swirler

“…Past numerical studies for helical axial swirler type systems were limited to the study of one or two cases of non-reacting/ reacting flows and very limited parametric studies of single swirler (Im et al, 2001;Ren et al, 2016;Heath, 2016;Fu et al, 2007) on aerodynamics and emissions were performed. To capture the rapid fuel-air mixing and recirculation zones, unsteady numerical methods like LES are suitable for resolving all the turbulent eddies (Dewanji et al, 2011(Dewanji et al, , 2010, and a detailed flow investigation of confinement effect on a single helical swirler using LES is studied. The preliminary part of this manuscript presents a non-reacting LES simulation of a single element swirler describing the meshing requirements for LES to capture the required energy spectrum for more reasonable accurate results in the core region of interest.…”

“…It can model and predict the unsteady effects of the flow field generated by the complex physical features. Dewanji et al (2011) performed numerical investigation using conventional turbulence models such as the Reynolds averaged Navier Stokes (RANS) model to simulate the reacting flow in a single-element LDI combustor, which captures the unsteady effects; steady RANS predictions were further extended to unsteady numerical methods like Unsteady Reynolds averaged Navier Stokes (URANS) and large eddy simulation (LES). The mean and turbulent velocity components of the single-element LDI predicted from the URANS simulation were in good agreement with the experiments.…”