A numerical study on the effect of cavitation erosion in a Diesel injector

The consequences of geometry alterations in a Diesel injector caused by cavitation erosion are inves-tigated with numerical simulations. The differences in the results between the nominal design geometryand the eroded one are analyzed for the internal injector flow and spray formation. The flow in the in-jector is modeled with a 3–phase Eulerian approach using a compressible pressure–based multiphase flowsolver. Cavitation is simulated with a non–equilibrium mass transfer rate model based on the simplifiedform of the Rayleigh–Plesset equation. Slip velocity between the liquid–vapor mixture and the air isincluded in the model by solving two separate momentum conservation equations. The eroded injector isfound to result to a loss in the rate of injection but also lower cavitation volume fraction inside the nozzle.The injected sprays are then simulated with a Lagrangian method considering as initial conditions thepredicted flow characteristics at the exit of the nozzle. The obtained results show wider spray dispersionfor the eroded injector and shorter spray tip penetration

Metoda LES jako narzędzie do analizy fluktuacji ciśnienia dla kolejnych cykli pracy w silnikach benzynowych o wtrysku bezpośrednim

The Large Eddy Simulation method (LES) has become a powerful computational tool for the application to turbulent flows. It links the classical Reynolds Averaged Navier–Stokes (RANS) approach and Direct Numerical Simulation (DNS). This means that the large eddies are computed explicitly in a time-dependent simulation using the filtered Navier-Stokes equations. The LES resolves the large flow scales that depend directly on the geometry where the small scales are modelled by the subgrid-scale models. LES is expected to improve the description of the aerodynamic and combustion processes in Internal Combustion Engines. This paper addresses the topic of developing the combustion model GCM (Gradient Combustion model) for the Large Eddy Simulation (LES) method. Another part of this paper presents numerical investigations of cycle-to-cycle combustion pressure variability with comparison to experimental data. The Gradient Combustion model (GCM) based on the Turbulent Flame Speed Closure Model (TFSCM) is validated against the experimental data for a multi-cycle gasoline direct injection research engine (SCRE). It is shown that the introduced combustion model is stable and capable of proper representation of the experimental results which is one of the assets of the LES method.Metoda LES jest obecnie zaawansowanym narzędziem numerycznym do analizy przepływów turbulentnych. Metoda LES opiera się na połączeniu klasyczej metody uśredniania równań Naviera-Stokes (RANS) z bezpośrednią analizą numeryczną (DNS). Oznacza to, że duże struktury wirowe są rozwiązywane niejawnie poprzez filtrowanie równań Naviera-Stokesa. W metodzie LES oznacza to obliczanie przepływu dużej skali, który zależy od geometrii, podczas gdy przepływ w małej skali jest modelowany modelem podsiatkowym (ang. Sub-grid-scale models, SGS). Uważa się, że metoda LES pozwoli na poprawienie numerycznego opisu aerodynamiki i procesów spalania w silnikach tłokowych. Artykuł przedstawia wyniki prac rozwojowych nad modelem spalania w metodzie LES. Model GCM (model spalania oparty na metodzie gradientu) został zastosowany do obliczeń wielocyklicznych i ich weryfikacji z wynikami eksperymentalnymi. Wyniki eksperymentalne pozyskano z badań na jednocylindrowym silniku badawczym (SCRE) o wtrysku bezpośrednim. W pracy pokazano, że model spalania jest stabilny numerycznie oraz otrzymane wyniki są zgodne z wynikami eksperymentalnymi, co jest jedną z ważniejszych zalet metody LES

Three-dimensional finite element simulation of a polycrystalline copper specimen

International audienceThe application of crystal plasticity in finite element codes provides a virtual copy of a real grain structure, including stress–strain state and slip system activity. This paper presents, first, finite element computations of an oxygen-free, high-conductivity copper multicrystal under monotonic tension. A series of polishing operations are used to reveal the real three-dimensional (3-D) microstructure, so that the mesh is a full 3-D mesh. A single crystal plasticity model is used to represent the elasto-plastic behavior for each of the approximately 100 grains. The results obtained with a full 3-D mesh and an extended 2-D mesh with columnar grains are compared in order to check the bias introduced by a simplified mesh generation. The paper goes on to compare the computational results to experimental data obtained by orientation image microscopy and local strain field measurements. Local strain and lattice rotation fields are shown. Finally, the numerical results for the slip system activity are analyzed

Coupled simulations of nozzle flow, primary fuel jet breakup, and spray formation

Presented are two approaches for coupled simulations of the injector flow with spray formation. In the first approach the two-fluid model is used within the injector for the cavitating flow. A primary breakup model is then applied at the nozzle orifice where it is coupled with the standard discrete droplet model. In the second approach the Eulerian multi-fluid model is applied for both the nozzle and spray regions. The developed primary breakup model, used in both approaches, is based on locally resolved properties of the cavitating nozzle flow across the orifice cross section. The model provides the initial droplet size and velocity distribution for the droplet parcels released from the surface of a coherent liquid core. The major feature of the predictions obtained with the model is a remarkable asymmetry of the spray. This asymmetry is in agreement with the recent observations at Chalmers University where they performed experiments using a transparent model scaled-up injector. The described model has been implemented into AVL FIRE computational fluid dynamics code which was used to obtain all the presented results. Copyrigh