Modelling of Turbulent Spray Flames with Variable Degrees of Fuel Pre-Evaporation
Energy Process Engineering
Final Report Abstract
Large-eddy simulations (LES) have been coupled with a conditional moment closure (CMC) method for the computation of a series of turbulent spray flames. Studies within the first funding period gave reasonable results for the prediction of temperature and velocity profiles, but some limitations of the method became apparent. These limitations are primarily related to the upper limit in mixture fraction space. In order to enhance the applicability of the LES-CMC model, two new models are proposed. The first approach, called two-conditional moment approach, accounts for the existence of pre-evaporated fuel by introducing two sets of conditional moments based on different mixture fractions. The upper limit of the mixture fraction space is dynamically selected for the solution of the second set of conditional moments, and the corresponding CMC solution in a CFD cell is estimated by interpolation between the two conditional moments weighted by the amount of vapour emitted within the domain. The cell-filtered value is given by integration of the conditional moment across mixture fraction space using a bounded β-FDF for the distribution of the scalar. Overall, good agreement with the experimental results is found for all test cases, and the methodology is shown to be applicable to flames with a relatively wide range of fuel vapour concentrations as long as non-premixed combustion is the dominant combustion mode. The unconditional temperature profiles clearly show that the new approach improves the predictions of mean temperature especially along the centerline. Also, the better predictions of the temperature field improve the accuracy of the predicted mean axial droplet velocities. For the second approach, called extended CMC (CMCe), CMC is coupled with a tabulated chemistry that allows for spatial and temporal variations of the tabulated chemical composition. An additional LES-filtered transport equation for a reaction progress variable needs to be solved. CMCe ensures a reasonably accurate computation of the chemical source term of the LES-filtered reaction progress variable and of the conditional moments despite large fluctuations around the conditional means computed by the CMC equation. Local deviations from the conditional mean can be charaterized by the LES-filtered progress variable. CMCe is validated by comparison with experimental results and the accuracy of predictions is similar to the two-conditional moment approach.
Publications
- Large eddy simulation of turbulent acetone spray combustion with conditional moment closure, In 25. Deutscher Flammentag, Volume 2119 (2011), 233-240, VDI
Ukai, S., Kronenburg, A., and Stein O.T.
- LES-CMC of a dilute acetone spray flame, Proc. Combust. Inst., 34 (2013) 1643-1650
Ukai, S., Kronenburg, A., and Stein O.T.
- Imaging measurements and LES-CMC modeling of a partially-premixed turbulent dimethyl ether/air jet flame, Proc. Combust. Inst., 35 (2014)
Coriton, B., Zendehdel, M., Ukai, S., Kronenburg, A., Stein O.T., Im, S.-K., Gamba, M., and Frank, J.H.
(See online at https://doi.org/10.1016/j.proci.2014.06.042) - Large eddy simulation of dilute acetone spray flames using CMC coupled with tabulated chemistry, Proc. Combust. Inst., 35 (2014)
Ukai, S., Kronenburg, A., and Stein O.T.
(See online at https://doi.org/10.1016/j.proci.2014.06.013) - Simulation of Dilute Acetone Spray Flames with LES-CMC using two conditional moments, Flow Turbul. Combust., (2014)
Ukai, S., Kronenburg, A., and Stein O.T.
(See online at https://doi.org/10.1007/s10494-014-9565-1) - Certain aspects of conditional moment closure for spray flame modelling. S. 335-350 in: High Performance Computing in Science and Engineering ’14; Eds. W.E. Nagel, D.B. Kröner, M.M. Resch, Springer, Cham, 2015. - 978-3-319-10809-4
Ukai, S., Kronenburg, A., and Stein O.T.
(See online at https://doi.org/10.1007/978-3-319-10810-0_23)
