Abstract
Large Eddy Simulations (LES) with the Conditional Moment Closure (CMC) combustion model of swirling ethanol spray flames have been performed in conditions close to blow-off for which a wide database of experimental measurements is available for both flame and spray characterization. The solution of CMC equations exploits a three-dimensional unstructured code with a first order closure for chemical source terms. It is shown that LES/CMC is able to properly capture the flame structure at different conditions and agrees reasonably well with the measurements both in terms of mean flame shape and dynamic behaviour of the flame evaluated in terms of local extinctions and statistics of the lift-off height. Experimental measurements of the overall (liquid plus gaseous) mixture fraction, performed using the Laser-Induced Breakdown Spectroscopy technique, are also included allowing further assessment and validation of the numerical method. The sensitivity of the simulation results to the various boundary conditions is discussed.
Highlights
Spray flames approaching blow-off are characterized by strongly unsteady phenomena which can be considered quite challenging to be reproduced in numerical simulations
The results obtained with the Large Eddy Simulations (LES)/Conditional Moment Closure (CMC) method will be compared with experimental measurements [31]
Comparisons between numerical and experimental statistics of the lift-off height from the outer anchoring part will be shown, to provide an assessment of the accuracy of the model to capture the degree of local extinction there
Summary
Spray flames approaching blow-off are characterized by strongly unsteady phenomena which can be considered quite challenging to be reproduced in numerical simulations. Our simulation capability of ignition and extinction phenomena is not fully validated yet, not least because capturing the local extinction and its evolution into a global blow-off has not been extensively demonstrated with current generation turbulent combustion models. In order to further assess the capability of the present numerical approach to predict the complex interactions between the evaporating spray and the reacting field, novel measurements of the overall (i.e. liquid plus vapour) mixture fraction, made possible by the Laser Induced Breakdown Spectroscopy (LIBS) technique, are presented and compared with the numerical results
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