Abstract
The evaluation of Internal Combustion Engine (ICE) flows by 3D-CFD strongly depends on a combination of mutually interacting factors, among which grid resolution, closure model, numerics. A careful choice should be made in order to limit the extremely high computational cost and numerical problems arising from the combination of refined grids, high-order numeric schemes and complex geometries typical of ICEs. The paper focuses on the comparison between different grid strategies: in particular, attention is focused firstly on near-wall grid through the comparison between multi-layer and single-layer grids, and secondly on core grid density. The performance of each grid strategy is assessed in terms of accuracy and computational efficiency. A detailed comparison is presented against PIV flow measurements of the Spray Guided Darmstadt Engine available at the Darmstadt University of Technology. As many research groups are simultaneously working on the Darmstadt engine using different CFD codes and meshing approaches, it constitutes a perfect environment for both method validation and scientific cooperation. A motored engine condition is chosen and the flow evolution throughout the engine cycle is evaluated on two different section planes. Pros and cons of each grid strategy are highlighted and motivated.
Highlights
CFD simulation of in-cylinder flows is a fundamental tool during the design and development of new Internal Combustion Engine (ICE) concepts
The Darmstadt Spray-Guided Engine operated under motored condition is simulated and each grid strategy is evaluated in terms of computational efficiency and fidelity of the outcomes to the measured particle image velocimetry (PIV) flow fields
Three consecutive Reynolds Averaged Navier Stokes (RANS) cycles are carried out for each of the above-mentioned grids to discard dependency of the results on the initial conditions; results of the latest cycles are shown in the present paper for the sake of brevity
Summary
CFD simulation of in-cylinder flows is a fundamental tool during the design and development of new ICE concepts. The available literature acknowledges the remarkable potential of Large Eddy Simulation (LES) as opposite to the more standardized Reynolds Averaged Navier Stokes (RANS) to simulate the turbulent nature of engineering flows [24] Such turbulent nature is primarily responsible for cycle-to-cycle variability of incylinder phenomena, which in turn severely affects efficiency. A two-layer all y+ model is adopted; a multi-layer near-wall cell grid is compared to a single layer one to assess the performance in terms of quality of results vs computational effort To this aim, the Darmstadt Spray-Guided Engine operated under motored condition is simulated and each grid strategy is evaluated in terms of computational efficiency and fidelity of the outcomes to the measured particle image velocimetry (PIV) flow fields.
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