SINOPSIS

Combustion noise generation from an open turbulent spray flame with Ethanol as the fuel is investigated using Direct Numerical Simulation (DNS). The multiphase reactive flow is simulated using an Eulerian/Lagrangian approach. The governing equations for the carrier gas phase are solved in an Eulerian framework, whereas the motions of the evaporating Ethanol droplets are tracked in a Lagrangian framework. A two-step global reaction mechanism is used to model Ethanol combustion. Two simulations are performed, one without considering radiative heat loss from the flame, while the other in which radiative heat loss is accounted for using an optically thin radiation model. The influence of radiative heat loss on the statistical flow field quantities and combustion noise is also investigated. The DNS results for velocity statistics of droplets show an overall good agreement with measurements and are virtually unaffected by the radiative heat loss source term, however the predictions for gas-phase excess temperature improve by taking radiative heat loss into consideration and show acceptable agreement with experimental data. The spectral content of the noise generated by the spray flame is broadband in nature. Furthermore, analysis of the noise directivity of the open turbulent spray flame indicates dominance of the monopole combustion noise sources due to the fluctuating heat release rate. Spectral content of combustion noise obtained from both simulations (with and without radiative heat loss) show subtle differences, but the range of noise intensities remain virtually similar for both cases indicating only a minor influence of the radiative heat loss on combustion generated noise. Furthermore, gradual suppression of noise emissions at high frequencies is observed with decreasing emission angle with respect to the flame axis in both cases.