Papers by Andrea Montorfano
A Study of the Organized in-Cylinder Motion by a Dynamic Adaptive Scale-Resolving Turbulence Model
The feasibility of using a scale-adaptive turbulence model for the simulation of the unsteady flo... more The feasibility of using a scale-adaptive turbulence model for the simulation of the unsteady flow in Internal Combustion (IC) Engines is investigated. The original theory of the Dynamic Length-Scale Resolution Model (DLRM), which includes an adaptive rescaling procedure for the modeled turbulent length and time scales, has been trimmed and applied to the simulation of the flow field of a geometrically simplified square-piston engine working under motored conditions. The flow field exhibits a strong tumbling motion, which is a major characteristic of modern turbo-charged, direct-injection gasoline engines. Multiple consecutive cycles have been computed and turbulent statistics, including the ensemble mean and the variance of the velocity field, have been compared with both experimental measurements and simulation results predicted by URANS and conventional LES with identical numerical setups.
- novel compressible dynamic solver for topoChanges
- combination of AMI and topoChanges
- hybr... more - novel compressible dynamic solver for topoChanges
- combination of AMI and topoChanges
- hybrid RANS/LES turbulence modeling
High-fidelity simulations of turbulent flows require highly resolved grids, leading to unacceptab... more High-fidelity simulations of turbulent flows require highly resolved grids, leading to unacceptably large computational wall-time even on large supercomputers. In an attempt to address these conflicting constraints, we propose the use of a hybrid LES/RANS scale-adaptive turbulence model, where a novel formulation of a dynamic filter allows to define what can be resolved by the computational grid and time step on the basis of the modeled length and time scales. The approach greatly reduces the overall grid-points in the simulation while also fully resolving regions of high-turbulence. A previously developed algorithm for dynamic mesh generation with topological changes was enhanced and coupled with fast, robust compressible segregated flow solvers. These algorithmic developments were made keeping in mind important considerations of load-balancing in order to achieve good strong scaling on modern supercomputers. Massively parallel simulations, which ran on up to 1024 cores on the supercomputers at Argonne National Lab, were conducted on several different test-cases: the dynamic VOF simulation of multi-hole high-pressure injector, a square piston engine with a guillotine moving valve and test cases from the ERCOFTAC database.
The dynamics and evolution of the turbulent flow inside an experimentally investigated engine-lik... more The dynamics and evolution of the turbulent flow inside an experimentally investigated engine-like geometry consisting of a flat-top cylinder head with a fixed, axis-centered valve and low-speed piston were studied numerically by means of Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES), with a particular focus on Cycle-to-Cycle Variability (CCV). DNS was performed by the spectral element code nek5000 on a 58M points grid, whereas LES was carried out by the finite volume software OpenFOAM on a 4.6M hexahedral mesh. Results obtained by DNS and LES are compared with respect to the velocity means and fluctuations, as well with other derived quantities, achieving good agreement between simulations and experiments. The cyclic variability and complex unsteady flow features like the laminar-to-turbulent transition and the evolution of the tumble vortices were studied by time-resolved analysis and Proper Orthogonal Decomposition (POD). Simulations show that 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, the 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 strong effect on the jet breakup process and the dynamics of the vortex ring below the valve of the subsequent cycle as well as on the observed significant cyclic variations.
The paper focuses on the development of a mesh moving method based on non-conformal topologically... more The paper focuses on the development of a mesh moving method based on non-conformal topologically changing grids applied to the simulation of IC engines, where the prescribed motion of piston and valves is accomplished by rigidly translating the sub-domain representing the moving component. With respect to authors previous work, a more robust and efficient algorithm to handle the connectivity of non-conformal interfaces and a mesh-motion solver supporting multiple layer addition/removal of cells, to decouple the time-step constraints of the mesh motion and of the fluid dynamics, has been implemented as a C ++ library to extend the already existing classes for dynamic mesh handling of the finite-volume, open-source CFD code OpenFOAM ®. Other new features include automatic decomposition of large multiple region domains to preserve processors load balance with topological changes for parallel computations and additional tools for automatic preprocessing and case setup. Finally, a transient solver for compressible viscous flows based on the transient SIMPLE algorithm has been implemented in order to enhance conservation of mass and energy for domains sliding over dynamically attached/detached boundaries. The advantages are significant: mesh changes in terms of topology and deformation are fully managed by the mesh motion solver without remeshing, with a consequent reduction of the overall simulation time. Most important, the method allows to preserve the quality of the mesh initially defined by the user (skewness, non-orthogonality and aspect ratio) during the whole engine cycle, favoring a faster convergence of the solver and a very accurate fluid-dynamic solution. Used in conjunction with LES turbulence modeling, the method allows to decouple mesh motion by LES filter operation, since the filter width is kept constant during the entire cycle. Validation tests have been performed on the full-cycle simulation of a Transparent Combustion Chamber (TCC) engine, whose experimental data are available through the Engine Combustion Network database (ECN). The implementation of the described methodology is absolutely general, it works on any number of processors and it can be applied to any application where moving parts and non-conformal interfaces are involved.
Computers & Fluids, 2014
Large Eddy Simulation (LES) has become an attractive simulation method even for technical process... more Large Eddy Simulation (LES) has become an attractive simulation method even for technical processes and it usually provides space and time resolved fluctuations of a significant portion of the spectrum. However, in contrast to a RANS simulation an accurate LES requires the definition of suitable initial and boundary conditions, which includes turbulent structures with physically sound spatial and temporal correlations. Such turbulent structures are usually generated artificially at the boundary. Three different algorithms for generating turbulent fluctuations are evaluated in the present work. The investigated methods are Filtered noise (Klein et al. [1]), Diffused noise (Kempf et al. [2]) and an Inverse Fourier approach (Billson [3], Davidson [4]).
Comparison of Direct and Large Eddy Simulations of the Turbulent Flow in a Valve/Piston Assembly
Flow, Turbulence and Combustion, 2015
ABSTRACT The dynamics and evolution of the turbulent flow inside an experimentally investigated e... more ABSTRACT The dynamics and evolution of the turbulent flow inside an experimentally investigated engine-like geometry consisting of a flat-top cylinder head with a fixed, axis-centered valve and low-speed piston were studied numerically by means of Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES), with a particular focus on Cycle-to-Cycle Variability (CCV). DNS was performed by the spectral element code nek5000 on a 58M points grid, whereas LES was carried out by the finite volume software OpenFOAM on a 4.6M hexahedral mesh. Results obtained by DNS and LES are compared with respect to the velocity means and fluctuations, as well with other derived quantities, achieving good agreement between simulations and experiments. The cyclic variability and complex unsteady flow features like the laminar-to-turbulent transition and the evolution of the tumble vortices were studied by time-resolved analysis and Proper Orthogonal Decomposition (POD). Simulations show that 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, the 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 strong effect on the jet breakup process and the dynamics of the vortex ring below the valve of the subsequent cycle as well as on the observed significant cyclic variations.
A Scale Adaptive Filtering Technique for Turbulence Modeling of Unsteady Flows in IC Engines
SAE International Journal of Engines, 2015
ABSTRACT Swirling flows are very dominant in applied technical problems, especially in IC engines... more ABSTRACT Swirling flows are very dominant in applied technical problems, especially in IC engines, and their prediction requires rather sophisticated modeling. An adaptive low-pass filtering procedure for the modeled turbulent length and time scales is derived and applied to Menter' original number k-omega SST turbulence model. The modeled length and time scales are compared to what can potentially be resolved by the computational grid and time step. If the modeled scales are larger than the resolvable scales, the resolvable scales will replace the modeled scales in the formulation of the eddy viscosity; therefore, the filtering technique helps the turbulence model to adapt in accordance with the mesh resolution and the scales to capture. The model has been implemented in a C++ library to extend the already existing capabilities of the finite-volume, open-source CFD code OpenFOAM(R): numerical simulations have been carried out both on strongly swirling flow through a sudden expansion and on a simple IC engine geometry with one axial central valve. The model seems able to capture unsteady effects and to produce accurate time-averaged results (especially if compared to its standard RANS formulation) and looks particularly suitable when used with grids where turbulence would not be sufficiently resolved for an accurate LES.
SAE Technical Paper Series, 2015
The paper focuses on the development of a mesh moving method based on non-conformal topologically... more The paper focuses on the development of a mesh moving method based on non-conformal topologically changing grids applied to the simulation of IC engines, where the prescribed motion of piston and valves is accomplished by rigidly translating the sub-domain representing the moving component. With respect to authors previous work, a more robust and efficient algorithm to handle the connectivity of non-conformal interfaces and a mesh-motion solver supporting multiple layer addition/removal of cells, to decouple the time-step constraints of the mesh motion and of the fluid dynamics, has been implemented as a C++ library to extend the already existing classes for dynamic mesh handling of the finite-volume, open-source CFD code OpenFOAM ® . Other new features include automatic decomposition of large multiple region domains to preserve processors load balance with topological changes for parallel computations and additional tools for automatic preprocessing and case setup. Finally, a transient solver for compressible viscous flows based on the transient SIMPLE algorithm has been implemented in order to enhance conservation of mass and energy for domains sliding over dynamically attached/detached boundaries. The advantages are significant: mesh changes in terms of topology and deformation are fully managed by the mesh motion solver without remeshing, with a consequent reduction of the overall simulation time. Most important, the method allows to preserve the quality of the mesh initially defined by the user (skewness, non-orthogonality and aspect ratio) during the whole engine cycle, favoring a faster convergence of the solver and a very accurate fluid-dynamic solution. Used in conjunction with LES turbulence modeling, the method allows to decouple mesh motion by LES filter operation, since the filter width is kept constant during the entire cycle. Validation tests have been performed on the full-cycle simulation of a Transparent Combustion Chamber (TCC) engine, whose experimental data are available through the Engine Combustion Network database (ECN). The implementation of the described methodology is absolutely general, it works on any number of processors and it can be applied to any application where moving parts and non-conformal interfaces are involved.
High resolution central schemes for multi-dimensional non-linear acoustic simulation of silencers in internal combustion engines
Mathematical and Computer Modelling, 2011
ABSTRACT Because of their small numerical viscosity even when very small time steps are enforced,... more ABSTRACT Because of their small numerical viscosity even when very small time steps are enforced, central schemes look very suitable for acoustic simulations of silencers in internal combustion engines. In this work, a high resolution central scheme has been used with ad-hoc developed boundary conditions for the generation of different acoustic perturbations (white noise, sweep, impulse) in the OpenFOAM® technology. The temporal solution, carried out by a first-order integration of the conservation laws by the explicit Euler’s method, has been first transferred into the frequency domain using FFT and then it has been processed to evaluate the transfer function of different geometries of silencers for internal combustion engines. The results obtained from the simulations have been compared with experimental data.
SAE Technical Paper Series, 2014
The dynamics and evolution of turbulent structures inside an engine-like geometry are investigate... more The dynamics and evolution of turbulent structures inside an engine-like geometry are investigated by means of Large Eddy Simulation. A simplified configuration consisting of a flat-top cylinder head with a fixed, axis-centered valve and low-speed piston has been simulated by the finite volume CFD code OpenFOAM ® ; the standard version of the software has been extended to include the compressible WALE subgrid-scale model, models for the generation of synthetic turbulence, some improvements to the mesh motion strategy and algorithms for LES data post-processing. In order to study both the initial transient and the quasi-steady operating conditions, ten complete engine cycles have been simulated. Phase and spatial averages have been performed over cycles three to ten in order to extract first and second moment of velocity; these quantities have then been used to validate the numerical procedure by comparison against experimental data. Complex unsteady features of turbulent fields like laminar-to-turbulent transition and tumble vortexes evolution have been studied either by time-resolved analysis and Proper Orthogonal Decomposition (POD). In addition, the cycle-to-cycle variations of flow field due to turbulent unsteadiness has been investigated by statistical analysis. Despite the present study has been carried out on a simplified geometry, it shows that LES can be a reliable tool not only for predicting averaged quantities (mean velocity and Reynolds stresses), but also to reproduce the dynamic behavior of complex turbulent structures in IC engines.
Wall-adapting subgrid-scale models to apply to large eddy simulation of internal combustion engines
International Journal of Computer Mathematics, 2014
ABSTRACT In this work a methodology to perform large eddy simulation of in-cylinder flows by the ... more ABSTRACT In this work a methodology to perform large eddy simulation of in-cylinder flows by the open-source CFD code OpenFOAM® is presented. First, authors implemented the dynamic Smagorinsky and the wall-adapting local eddy-viscosity (WALE) subgrid-scale model in the code; model validation has been performed by comparison against experiments carried out on a standard test case of flow with separation and recirculation. The WALE model has been further applied on a simplified engine-like geometry. Also in this case results look satisfying, although discrepancies still exist between simulations and experiments. An explanation for such a behaviour is suggested in the paper, together with a possible solution.
Re´sume´-Conditions aux limites et mode`les SGS pour les simulations LES d'e´coulements se´pare´s... more Re´sume´-Conditions aux limites et mode`les SGS pour les simulations LES d'e´coulements se´pare´s de´limite´s par des parois : une application aux ge´ome´tries de type moteur -L'imple´mentation et la combinaison de conditions aux limites avance´es et de mode`les des e´chelles infe´rieures a`la maille dans des simulations des grandes e´chelles (Large Eddy Simulations, LES) sont pre´sente´es. Le but est d'effectuer des simulations LES fiables des e´coulements froids dans des ge´ome´tries complexes, comme dans les cylindres des moteurs a`combustion interne. L'imple´mentation de conditions aux limites a`l'entre´e pour la ge´ne´ration de turbulence synthe´tique et de deux mode`les des e´chelles infe´rieures a`la maille, le mode`le local dynamique de Smagorinsky et le mode`le SGS (Sub-Grid Scales) de viscosite´WALE (Wall-Adapting Local Eddy), est de´crite. Le mode`le WALE est baseś ur le carre´du tenseur du gradient de vitesse. Il prend en compte a`la fois les effets de la pression et du taux de rotation des plus petites fluctuations turbulentes de´tectables et il de´crit de manie`re ade´quate l'e´chelle y 3 a`proximite´des parois de la viscosite´turbulente sans ne´cessiter de pression dynamique. Il est ainsi cense´repre´senter un mode`le tre`s fiable pour les simulations ICE. La validation du mode`le a e´te´effectue´e sur deux bancs laminaires stationnaires : une ge´ome´trie a`gradin inverse´(backward-facing) et une ge´ome´trie simple de moteur a`combustion interne avec une unique vanne centrale. L'exhaustivite´de la simulation LES (i.e. la qualite´de la simulation LES) est aussi discute´e.
Conference Presentations by Andrea Montorfano
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Papers by Andrea Montorfano
- combination of AMI and topoChanges
- hybrid RANS/LES turbulence modeling
Conference Presentations by Andrea Montorfano
- combination of AMI and topoChanges
- hybrid RANS/LES turbulence modeling