Due to its positive effect on flame propagation in the case of a well-defined breakdown, the formation of a large-scale tumble motion is an important goal in engine development. Cycle-to-cycle variations (CCV) in the tumble position and strength however lead to a fluctuating tumble breakdown in space and time and therefore to combustion variations, indicated by CCV of the peak pressure. This work aims at a detailed investigation of the large-scale tumble motion and its interaction with the piston boundary layer during the intake stroke in a state-of-the-art gasoline engine. To allow the validation of the flow near the piston surface obtained by simulation, a new measurement technique called "Flying PIV" is applied. A detailed comparison between experimental and simulation results is carried out as well as an analysis of the obtained flow field. The large-scale tumble motion is investigated based on numerical data of multiple highly resolved intake strokes obtained using scale-resolving simulations. A method to detect the tumble center position within a 3D flow field, as an extension of previously developed 2D and 3D algorithms, is presented and applied. It is then used to investigate the phase-averaged tumble structure, its characteristics in terms of angular velocity and the CCV between the individual intake strokes. Finally, an analysis is presented of the piston boundary layer and how it is influenced by the tumble motion during the final phase of the intake stroke.
-Modern spark-ignited internal combustion engines have intake ports designed to introduce high levels of so-called "tumble" charge motion. Correspondingly high shear rates can lead to high fluctuations and turbulence within the combustion chamber. A suitable test case to characterize the intake flow is a steady-state flow bench. Although routinely used in the engine development process to determine the global discharge coefficients, only a few detailed numerical and experimental studies use this test case to analyze the flow in the vicinity of the valve with high spatial and temporal resolution. In this paper, we combined highly resolved two-dimensional, two-component Particle Image Velocimetry (PIV) measurements and numerical simulations using a Detached-Eddy Simulation (DES) model to characterize engine-relevant flow features on a flow bench. The spatial resolution of numerical simulations on two different grids is assessed and compared to that of the PIV measurement. The results of simulations and experiment are then compared in terms of their mean and fluctuation velocity fields and the jet orientation. A detailed study of the area around the valve seats investigates the validity of wall functions in this region. Finally, we examine structures induced by vortex-shedding at the valve stem and if they are transported into the combustion chamber.Résumé -Étude numérique et expérimentale résolue dans l'espace de l'écoulement à travers le conduit d'admission d'un moteur à combustion interne -Les moteurs à combustion interne modernes à allumage commandé disposent de conduits d'admission conçus pour générer des niveaux importants de mouvements de charge dits « tumble ». Les niveaux importants de taux de cisaillement qui en résultent peuvent conduire à de fortes fluctuations et turbulences dans la chambre de combustion. Un cas test adapté pour caractériser l'écoulement d'admission est un banc volute. Bien que son utilisation durant les phases de conception moteur pour déterminer les coefficients de perte de charge globaux soit très répandue, seules quelques études numériques et expérimentales détaillées utilisent ce test pour étudier l'écoulement au voisinage de la soupape avec des résolutions spatiales et temporelles élevées. Dans le présent article, nous avons combiné des mesures PIV bi-composants, bidimensionnelles hautement résolues et des simulations numériques utilisant une approche de type « Detached-Eddy Simulation » pour caractériser des structures d'écoulement d'importance pour le moteur sur un banc volute. La résolution spatiale des simulations numériques est évaluée sur deux maillages et comparée à celle de la mesure « Particle Image Velocimetry », PIV. Les résultats numériques et expérimentaux sont ensuite comparés en termes de champ de vitesse moyen et
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