Direct numerical simulation of multiple cycles in a valve/piston assembly

Abstract

The dynamics and multiple-cycle evolution of the incompressible flow induced by a moving piston through the open valve of a motored piston-cylinder assembly was investigated using direct numerical simulation. A spectral element solver, adapted for moving geometries using an Arbitrary Lagrange/Eulerian formulation, was employed. Eight cycles were simulated and the ensemble- and azimuthally-averaged data were found to be in good agreement with experimentally determined means and fluctuations at all measured points and times. During the first half of the intake stroke the flow field is dominated by the dynamics of the incoming jet and the vortex rings it creates. With decreasing piston speed a large central ring becomes the dominant flow feature until the top dead center. The flow field at the end of the previous cycle is found to have a dominant effect on the jet breakup and the vortex ring dynamics below the valve and on the observed significant cyclic variations. Based on statistical averaging, the evolution of the turbulent flow field during the first half of the intake stroke is dominated by the jet breakup process leading to a strongly anisotropic behavior. In the second part of the intake stroke, the decrease of the incoming jet velocity results in a more isotropic behavior.

Scale-resolving simulations in engine combustion process design based on a systematic approach for model development

“…51 More recently, this setup was even investigated using DNS by the ETH Zu¨rich group [31][32][33][34] including studies of the jet breakup, boundary layer wall heat transfer and thermal stratification. Such data are perfectly suited for model development and validation (see section ''Approach for systematic model evaluation and development for scale-resolving engine simulations'').…”

“…[31][32][33][34] Despite the significant differences with respect to current engines, many flow patterns such as large-scale vortex formation and interaction with the in-cylinder flow field can be studied taking advantage of the richness of the DNS data. Schmitt et al 32 looked at jet breakup and how it is influenced by the residual flow motion in the cylinder to identify the origin of CCV.…”

Identification of Large-Scale Structure Fluctuations in IC Engines using POD-Based Conditional Averaging

“…Due to the simplicity of the geometry, this setup is suitable for the first analysis. The direct numerical simulations by Schmitt et al [34] provide a very detailed insight into the complex flow structure inside the combustion chamber and confirmed an axisymmetric average flow field as well as axial symmetry for the coherent large-scale and small-scale structures. The data sets are generated from slices rotated around the cylinder axis with a non-dimensional radius of 0:2 to 1 (Fig.…”

“…The first case, based on a simplified engine geometry, is meant to investigate the workflow in general in a welldefined and geometrically simple setup, which however still retains a significant number of engine specific characteristics. Numerical studies of this engine have been published by several authors [33][34][35].…”

12th International Congress of Engine Combustion Processes: Current problems and modern techniques (ENCOM2015)

“…4 The DNS technique is surely the most sophisticated simulation technique developed so far with only very few nearengine applications. [15][16][17] In this Special Issue, it is the first investigation being focused on engine-relevant conditions. In an additional numerical simulation article, Pasternak et al 9 used a zero-dimensional (0D) spark ignition stochastic reactor model (SI-SRM) and a three-dimensional (3D) computational fluid dynamics (CFD) engine model for the prediction of combustion and knock occurrence in SI gasoline engines.…”