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Papers by Andrea Aprovitola

SUMMARY The numerical simulation of turbulence is one of the most challenging tasks in the field ... more SUMMARY The numerical simulation of turbulence is one of the most challenging tasks in the field of the modern computational science. At present, the most advanced approach is the large eddy simulation (LES) technique wherein a formal separation between resolved (large) and unresolved (small) scales of the motion is in effect by means of a filtering operation applied onto the governing equations. However, LES requires very sophisticated numerical discretizations in terms of both accuracy and efficiency.

Large Eddy Simulation (LES) of turbulent flows is based on the idea of directly computing the dyn... more Large Eddy Simulation (LES) of turbulent flows is based on the idea of directly computing the dynamics of the flow scales responsible for the energy transfer, while modeling the dynamics of the scales where dissipation takes place. Although LES has a reduced cost with respect to Direct Numerical Simulation, where all the scales are solved, it is a computationally expensive technique, and its application to realistic flows is a usual context for high-performance computing.

Entrained-flow gasifiers are characterized by operating conditions that promote ash migration/dep... more Entrained-flow gasifiers are characterized by operating conditions that promote ash migration/deposition onto the reactor walls, whence the ash is drained as a molten phase. Previous investigations have shed light on the fate of char particles as they impinge on the wall slag layer: both char entrapment inside the melt and carbon-coverage of the slag can occur, as suggested by experimental investigation of ashes generated by full-scale plants.

SUMMARY. This paper summarizes the activity of the LESinItaly group in a project supported by the... more SUMMARY. This paper summarizes the activity of the LESinItaly group in a project supported by the CASPUR centre during the year 2010. Commercial, open-source and own-made LES codes were tested by several units in the simulation of the turbulent flow in a plane channel. The codes produced solutions on two different grids, providing also the corresponding no-model solutions.

Abstract Entrained-flow gasifiers are characterized by operating conditions that promote ash migr... more Abstract Entrained-flow gasifiers are characterized by operating conditions that promote ash migration/deposition onto the reactor walls, whence the ash is drained as a molten phase. Previous investigations have shed light on the fate of char particles as they impinge on the wall slag layer: both char entrapment inside the melt and carbon-coverage of the slag can occur, as suggested by experimental investigation of ashes generated by full-scale plants.

SUMMARY This work illustrates how the open source OpenFOAM CFD library can be adopted to develop ... more SUMMARY This work illustrates how the open source OpenFOAM CFD library can be adopted to develop different numerical modelling approaches that can be jointly used to understand the fate of char particles in full-scale entrained-flow coal gasifiers operated in the slagging regime.

Abstract This work describes the results achieved analyzing the complex phenomenology associated ... more Abstract This work describes the results achieved analyzing the complex phenomenology associated with interaction of a particle-laden turbulent flow with the slag-covered wall of an entrained flow gasifier. Two approaches are considered to address coal particle fate: experimental analysis of sample collected in operating gasifiers and a new numerical simulation approach based on a multilevel modeling.

Abstract. We discuss the design and development of a parallel code for Large Eddy Simulation (LES... more Abstract. We discuss the design and development of a parallel code for Large Eddy Simulation (LES) by exploiting libraries for sparse matrix computations. Specifically, we show how a numerical procedure for the LES of turbulent channel flows, based on an approximate projection method, can be formulated in terms of linear algebra operators involving sparse matrices and vectors, and can be implemented using general-purpose linear algebra libraries as building blocks.

Journal of Computational Physics, Jan 1, 2004

Upwind schemes were judged inappropriate for performing accurate large eddy simulations of turbul... more Upwind schemes were judged inappropriate for performing accurate large eddy simulations of turbulent flow owing to the artificial dissipation that is present at high wavenumbers of the energy content. Such a conclusion has been drawn also from some results obtained by adopting Finite Difference schemes. The present paper illustrates the performances of some new Finite Volume upwind discretization of the convective terms in the case of the 1-D Burgers model equation while studying the effects of numerical discretization on several Sub-Grid Scales turbulence models, starting from the classical static and dynamic eddy viscosity models through the recent deconvolution-based ones. Basing on previously published papers, large eddy simulations along with a deconvolution-based procedure for de-filtering the evolving variable, have been originally developed and applied. It will be shown how the coherent application of the procedure allows us to develop high-order accurate Finite Volume upwind schemes, which maintain a good spectral resolution in the entire range of resolved scale. Such schemes can be candidate for performing accurate simulations of real turbulence.

International journal for numerical …, Jan 1, 2007

Abstract Second-order accurate projection methods for simulating time-dependent incompressible fl... more Abstract Second-order accurate projection methods for simulating time-dependent incompressible flows on cell-centred grids substantially belong to the class either of exact or approximate projections. In the exact method, the continuity constraint can be satisfied to machine-accuracy but the divergence and Laplacian operators show a four-dimension nullspace therefore spurious oscillating solutions can be introduced. In the approximate method, the continuity constraint is relaxed, the continuity equation being satisfied up to ...

Quality and Reliability of Large-Eddy …, Jan 1, 2008

Filtering in Large Eddy Simulation (LES) is often only a formalism since practically discretizati... more Filtering in Large Eddy Simulation (LES) is often only a formalism since practically discretization of both the domain and operators is used as implicit grid-filtering to the variables. In the present study, the LES equations are written in the integral form around a Finite Volume (FV) Ώ rather than in the differential form as is more usual in Finite Differences (FD) and Spectral Methods (SM). Grid-filtering is therefore associated to the use of an explicit local volume average, by the way of surface flux integrals, and specific LES ...

ICAR-CNR Technical …, Jan 1, 2007

Consiglio Nazionale delle Ricerche. Tali rapporti, approntati sotto l'esclusiva responsabilità sc... more Consiglio Nazionale delle Ricerche. Tali rapporti, approntati sotto l'esclusiva responsabilità scientifica degli autori, descrivono attività di ricerca del personale e dei collaboratori dell'ICAR, in alcuni casi in un formato preliminare prima della pubblicazione definitiva in altra sede.

Large-Scale Scientific …, Jan 1, 2010

Abstract. This work is concerned with the application of algebraic multilevel preconditioners in ... more Abstract. This work is concerned with the application of algebraic multilevel preconditioners in the solution of pressure linear systems arising in the large eddy simulation of turbulent incompressible flows in wallbounded domains. These systems, coming from the discretization of elliptic equations with periodic and Neumann boundary conditions, are large and sparse, singular, compatible, and nonsymmetric because of the use of non-uniform grids taking into account the anisotropy of the flow. Furthermore, they generally ...