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CHT-04 - Advances in Computational Heat Transfer III. Proceedings of the Third International Symposium
April, 19-24, 2004, on board MS Midnatsol Norwegian Coastal Voyage

DOI: 10.1615/ICHMT.2004.CHT-04


ISBN Print: 978-1-56700-174-7

ISSN: 2578-5486

UNSTEADY METHODS (URANS AND LES) FOR SIMULATION OF COMBUSTION SYSTEMS

page 21
DOI: 10.1615/ICHMT.2004.CHT-04.30
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RESUMO

A great variety of flows with importance to practical engineering applications are inherently unsteady, and virtually all of the Newtonian fluid flows in nature are turbulent. In order to better capture the dynamics of such complex flows using feasible computational costs, it is more appropriate to use unsteady methods. The present overview is confined to single-phase turbulent flows and discuses some basic issues related to unsteady modeling methods. The first part of this paper provides an evaluation of the performance of the unsteady RANS (URANS) method in a comparative manner to LES and experimental data. It could be confirmed that the U-RANS method employing a full Reynolds stress model is able to capture unsteady phenomena, such as the precessing vortex core phenomenon both qualitatively and in parts also quantitatively. In the second part, some important features of combustion LES are recollected and some results based on the conserved scalar method in connection with the concept of sub-grid scale pdf are presented. A flamelet approach is used to relate the filtered mixture fraction to density, temperature and species concentrations. It is shown that LES is able to deliver good results very close to available measured data, where the flow is governed by large, turbulent structures. Flamelet chemistry appears well able to reproduce experimental data for species, in particular with regard to kinetic effects prediction, whereas equilibrium chemistry strongly deviates. However, a good predictability could be achieved when appropriate choice of boundary and inflow conditions is made. The use of the technique of numerical inflow-generation appears to be very helpful.

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