Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Complementing current databases and know-how for turbulence, wall treatment and mesh quality in engine codes

The high density variation at the wall is taken into account using a correction of the local heat transfer coefficient using a method developed at ERC (Wisconsin). New submodels for velocity-based and turbulent-kinetic energy based determination of heat transfer coefficient are implemented into the KIVA-3 code and as user-defined subroutine into STAR-CD.

The high density correction yields higher heat fluxes (by factor 2-2.5) than the conventional constant-density approach. Differences observed between KIVA and STAR-CD are explainable by the different treatment of boundary conditions for turbulent kinetic energy.

For both production and university research engines CFD simulations have been performed for a given set of operation points using the available set of models, regarding gas exchange, combustion process and local heat transfer, all these local phenomena considered to be relevant for NOx formation.

Comparison with crank-angle resolved measurements of wall heat fluxes confirms the implementation of the ERC-compressibility correction approach.

Global integral heat fluxes using Han-Reitz compressibility correction for incompressible wall functions with y+-values in the log-law validity range 10 < y+ < 100 correspond well with experimental data yielding slight over prediction in case of CFD-prediction. Example: O.P.:IMEP= 6bar: Over prediction by 13.6% (2000rpm), resp. 9.2% (3000rpm).

A mesh-correction technique has been developed such that the near-wall distance of all cells next to the combustion chamber wall is moved into the range of validity for the application of wall functions supplied by the university partners (Delft, KCL).

Heat transfer to components (piston, head, liner) may be properly described based on new dynamic mesh adaptation strategy to avoid y+-values outside the log-law validity range.

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