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Numerical simulation of pulsed and stratified combustion
This work numerically investigates pulsed jets and stratified combustion by large eddy simulation (LES) and direct numerical simulation (DNS). In the first part, the numerical models are tested and further developed to reproduce two well-known transient jet experiments. The first experiment is a non-reactive pulsed jet, where the mixing dynamics are investigated by comparing the pseudo-DNS with the experimental evidence. The second experiment is an auto-igniting pulsed jet where the chemistry is described first by a multi-dimensional pressure-sensitive tabulated chemistry method and afterwards by a direct chemistry approach with an advanced chemical mechanism for deeper analysis and validation. The cycle-to-cycle variations of a pulsed jet are analysed in terms of ignition dynamics and thermochemical states of minor species over the entire ignition duration. In the second part, the well-known turbulent stratified burner from Cambridge is simulated. Initially, the stratification effects on one-dimensional unsteady flames are investigated. The conventional flame speed definitions for premixed flames are extended for the stratified flame context. It is shown that even the reduced chemical mechanism can show strong stratification effects, which are amplified in strength when realistic diffusion velocity assumption is employed. The highly stratified Cambridge burner was then recomputed using tabulated chemistry with an artificially thickened flame approach to test the turbulent-flame interaction models. In turbulent flames, the lost flame surface due to the thickening of the flame is reintroduced by wrinkling models initially proposed for premixed flames. The applicability of these wrinkling models to stratified flames is tested. Finally, the moderately stratified Cambridge burner is simulated by pseudo-DNS and tabulated chemistry to analyse the turbulence and stratified flame interactions. The pseudo-DNS data-set is extracted into two separate zones consisting of either premixed or stratified modes of combustion. ...
Numerical simulation of pulsed and stratified combustion
This work numerically investigates pulsed jets and stratified combustion by large eddy simulation (LES) and direct numerical simulation (DNS). In the first part, the numerical models are tested and further developed to reproduce two well-known transient jet experiments. The first experiment is a non-reactive pulsed jet, where the mixing dynamics are investigated by comparing the pseudo-DNS with the experimental evidence. The second experiment is an auto-igniting pulsed jet where the chemistry is described first by a multi-dimensional pressure-sensitive tabulated chemistry method and afterwards by a direct chemistry approach with an advanced chemical mechanism for deeper analysis and validation. The cycle-to-cycle variations of a pulsed jet are analysed in terms of ignition dynamics and thermochemical states of minor species over the entire ignition duration. In the second part, the well-known turbulent stratified burner from Cambridge is simulated. Initially, the stratification effects on one-dimensional unsteady flames are investigated. The conventional flame speed definitions for premixed flames are extended for the stratified flame context. It is shown that even the reduced chemical mechanism can show strong stratification effects, which are amplified in strength when realistic diffusion velocity assumption is employed. The highly stratified Cambridge burner was then recomputed using tabulated chemistry with an artificially thickened flame approach to test the turbulent-flame interaction models. In turbulent flames, the lost flame surface due to the thickening of the flame is reintroduced by wrinkling models initially proposed for premixed flames. The applicability of these wrinkling models to stratified flames is tested. Finally, the moderately stratified Cambridge burner is simulated by pseudo-DNS and tabulated chemistry to analyse the turbulence and stratified flame interactions. The pseudo-DNS data-set is extracted into two separate zones consisting of either premixed or stratified modes of combustion. ...
Numerical simulation of pulsed and stratified combustion
Inanc, Eray (Autor:in) / Kempf, Andreas M.
01.02.2022
Hochschulschrift
Elektronische Ressource
Englisch
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