1,721,096 research outputs found
Gaspare Traversi ritrattista dello storico capuano Francesco Granata
No full textIl contributo presenta un nuovo Ritratto di Gaspare Traversi, il cui soggetto viene identificato nello storico e vescovo capuano Francesco Granata
Nota eorum quae in hoc libro continentur Oratio de laudibus Astrologiae habita a Bartholomeo Vespucio ... in almo Patauio Gymnasio anno M.d.vi. Textus sphaerae Ioannis de Sacro Busto. Expositio sphaerae ... Fra[n]cisci Capuani ... Annotatio[n]es no[n]null
No full textSacro Bosco, Joannes de. Textus sphaerae ; Capuano, Francesco. Expositio sphaerae ; Vespucci, Bartolomeo. Oratio de laudibus astrologiae ; Grosseteste, Robert. Sphaerae compendium ; Regiomontanus, Joannes. DisputationesA Res. 39/1/0
Parallelization of compact finite-volume schemes for turbulent compressible flow
No full textCompact schemes are widely employed in numerical simulations of turbulent flows, because of
their beneficial resolution properties and high overall accuracy.
However, the implicit nature of such methods makes them difficult to use in a parallel framework, especially when a MPI-based multi-block partitioning technique is adopted.
Previous attempts fall mainly into two categories:
1. use of parallel algorithms for solving the linear system of equations over the entire domain;
2. use of explicit or asymmetric stencils at block-to-block connections to obtain disjoint matrix systems.
While the first approach can suffer from low parallel efficiency, the second one has received considerable attention over the last years and is now an active field of research.
The main advantage of this procedure is to lead to disjoint matrix systems that can be solved independently by exchanging a (small) number of halo cells between the blocks. Unfortunately, breaking the global dependance results in altered dissipation and dispersion properties, which are well-known to be crucial in LES and DNS of turbulent flows. The aim of the present study is to construct a robust parallelization strategy for finite-volume compact schemes on multi-block domains. Particular attention is paid to spectral properties, conservativeness and accuracy of the resulting methods
Numerical and experimental characterization of a double-orifice synthetic jet actuator
No full textA complete investigation of a doubleorifice
synthetic jet actuator, focused on the device
frequency response in terms of jet velocity, has been
carried out. Numerical simulations have shown that, in
many operation conditions, the flow within the
actuator cavity can be considered as divided in two
sub-volumes, each characterized by its own flow field.
An analytical approach, based on the previous consideration,
has allowed to obtain simple relationships
for the three resonance frequencies and to provide
further insights on the jets formation. The model has
been validated through experimental tests carried out
on two actuators manufactured in-house, having
different geometrical and mechanical characteristics.
Comparisons with the behavior of the twin singleorifice
device have been discussed and useful considerations
on the prediction of the actual formation of
the synthetic jet are included
Effects of Numerical Errors in Large-Eddy Simulation of Transitional Wall-Bounded Flows
Full text linkEffects of numerical errors in large-eddy simulations of transitional wall-bounded flows are investigated. Temporal and spatial laminar-to-turbulent transition in both channel and pipe flows is simulated using second- and fourth-order accurate finite-volume solvers based on the open-source CFD package OpenFOAM. Starting from unperturbed laminar or plug-flow profiles, it is found that, for centered finite-volume discretization, the onset of primary instability and the subsequent nonlinear pattern are highly sensitive to rounding errors and depend on a multitude of parameters: grid resolution, initial base flow, number of processors, flux reconstruction scheme, temporal integration time-step and subgrid-scale model. An attempt aimed at identifying the different contributions coming from each parameter, the various sources of error and their influence on the transition scenario is given in the study
Nonlinear evolution of an isolated disturbance at two-phase flow interface
No full textThe nonlinear evolution of an isolated, finite-amplitude wave at the interface between two immiscible fluids of different density is simulated by means of a discrete vortex method. In contrast to a periodic disturbance, that evolves into the familiar train of Kelvin-Helmholtz (KH) linear rolls, the single-wave scenario possess unique features that are not yet well understood. The aim of the present contribution is to provide an in-depth description of the nonlinear wave evolution, and to highlight the different features that distinguish the nonlinear case from the classical KH model. The two-phase interface is represented by a discrete vortex sheet, whose dynamics is simulated by a point vortex method that accounts for density stratification, surface tension and gravity. It is found that the different topology of streamlines occurring in the two cases determine a nonlinear wave speed that is different from the one predicted by classical KH theory. The instability onset threshold, as well as other flowfield properties also change accordingly
An efficient time advancing strategy for energy-preserving simulations
No full textEnergy-conserving numerical methods are widely employed within the broad area of convection-dominated systems. Semi-discrete conservation of energy is usually obtained by adopting the so-called skew-symmetric splitting of the non-linear convective term, defined as a suitable average of the divergence and advective forms. Although generally allowing global conservation of kinetic energy, it has the drawback of being roughly twice as expensive as standard divergence or advective forms alone. In this paper, ageneral theoretical framework has been developed to derive an efficient time-advancement strategy in the context of explicit Runge–Kutta schemes. The novel technique retains the conservation properties of skew-symmetric-based discretizations at a reduced computa-tional cost. It is found that optimal energy conservation can be achieved by properly constructed Runge–Kutta methods in which only divergence and advective forms for the convective term are used. As a consequence, a considerable improvement in computational efficiency over existing practices is achieved. The overall procedure has proved to be able to produce new schemes with a specified order of accuracy on both solution and energy. The effectiveness of the method as well as the asymptotic behaviorof the schemes is demonstrated by numerical simulation of Burgers’ equation
PERFORMANCES OF TWO OPEN-SOURCE SOLVERS IN THE NUMERICAL SIMULATION OF SYNTHETIC JETS
No full textWe report direct numerical simulations of a synthetic jet issuing in a quiescent environment performed by two widespread open-source computational fuid dynamics
(CFD) codes: Nek5000 and the OpenFOAM solver pimpleFoam. While the former employs a high-order spectral-element method, the latter is based on finite-volume, lower-
order schemes. The
flow parameters are based on the experimental data of Yao et al.
(2006). The performances of the two codes are compared thoroughly, with regard to accuracy as well as computational cost. Our computations show that Nek5000 is globally
more efficient than pimpleFoam for the problem under study
Large-eddy simulation of a spatially-evolving turbulent mixing layer
No full textLarge-eddy simulations of a spatially-evolving turbulent mixing layer have been performed. The flow conditions correspond to those of a documented experimental campaign (Delville, Appl. Sci. Res. 1994). The flow evolves downstream of a splitter plate separating two fully turbulent boundary layers, with Re_theta = 2900 on the high-speed side and Re_theta = 1200 on the low-speed side. The computational domain starts at the trailing edge of the splitter plate, where experimental mean velocity profiles are prescribed; white-noise perturbations are superimposed to mimic turbulent fluctuations. The fully compressible Navier-Stokes equations are solved by means of a finite-volume method implemented into the in-house code SPARK-LES. The results are mainly checked in terms of the streamwise evolution of the vorticity thickness and averaged velocity profiles. The combined effects of inflow perturbations, numerical accuracy and subgrid-scale model are discussed. It is found that excessive levels of dissipation may damp inlet fluctuations and delay the virtual origin of the turbulent mixing layer. On the other hand, non-dissipative, high-resolution computations provide results that are in much better agreement with experimental data
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