This thesis investigates a numerical method to quickly assess the response of a laminar, premixed flame to equivalence ratio perturbations. This linearized reacting flow (LRF) solver relies on linearizing Navier-Stokes equations with reacting species equations. The governing equations are linearized around a steady operation point, while reaction and heat release terms are expressed with a linearized Arrhenius equation. The number of independent variables is kept low by exploiting analytic correlations from the reaction equation. Discretization is done by the discontinuous Galerkin finite element method. The linear system of equations is solved in frequency domain with the simulation software COMSOL 4.4 to compute the flame response functions (FRF). The LRF solver is applied to investigate attached and lifted laminar premixed flames in 2D for equivalence ratio perturbations. Results are compared to FRF identified from a CFD simulation. The phase of simulated FRFs is in excellent agreement with the reference data from CFD. Gain, however, is underestimated by the LRF solver for the attached flame and falsely predicts the excessive gain peak frequency for the lifted flame. Secondly, the LRF solver’s solution is examined towards the influence of mass fraction perturbations on enthalpy and temperature perturbations. Results show, that temperature is not influenced by mass fraction perturbations, while mass fraction perturbations have to be modelled for enthalpy perturbations.     «

This thesis investigates a numerical method to quickly assess the response of a laminar, premixed flame to equivalence ratio perturbations. This linearized reacting flow (LRF) solver relies on linearizing Navier-Stokes equations with reacting species equations. The governing equations are linearized around a steady operation point, while reaction and heat release terms are expressed with a linearized Arrhenius equation. The number of independent variables is kept low by exploiting analytic corre...     »

This thesis investigates a numerical method to quickly assess the response of a laminar, premixed flame to equivalence ratio perturbations. This linearized reacting flow (LRF) solver relies on linearizing Navier-Stokes equations with reacting species equations. The governing equations are linearized around a steady operation point, while reaction and heat release terms are expressed with a linearized Arrhenius equation. The number of independent variables is kept low by exploiting analytic correlations from the reaction equation. Discretization is done by the discontinuous Galerkin finite element method. The linear system of equations is solved in frequency domain with the simulation software COMSOL 4.4 to compute the flame response functions (FRF). The LRF solver is applied to investigate attached and lifted laminar premixed flames in 2D for equivalence ratio perturbations. Results are compared to FRF identified from a CFD simulation. The phase of simulated FRFs is in excellent agreement with the reference data from CFD. Gain, however, is underestimated by the LRF solver for the attached flame and falsely predicts the excessive gain peak frequency for the lifted flame. Secondly, the LRF solver’s solution is examined towards the influence of mass fraction perturbations on enthalpy and temperature perturbations. Results show, that temperature is not influenced by mass fraction perturbations, while mass fraction perturbations have to be modelled for enthalpy perturbations.     «

This thesis investigates a numerical method to quickly assess the response of a laminar, premixed flame to equivalence ratio perturbations. This linearized reacting flow (LRF) solver relies on linearizing Navier-Stokes equations with reacting species equations. The governing equations are linearized around a steady operation point, while reaction and heat release terms are expressed with a linearized Arrhenius equation. The number of independent variables is kept low by exploiting analytic corre...     »