Gino Bella

Lattice Boltzmann schemes without coordinates.

We discuss recent developments extending the scope of the lattice Boltzmann method to unstructured (coordinateless) grids with arbitrary connectivity. Besides their intrinsic interest as examples of discrete kinetic systems living in irregular phase–space, the above extensions bear a direct relevance as computational tools for multi–scale applications.

Nonlinear Stability of Compressible Thermal Lattice BGK Models

The nonlinear stability of thermal lattice BGK models is examined by means of computer simulation for the case of one- and two- dimensional compressible flows. It is shown that in one dimension (1D) the method is stable on a sizeable range of flow speeds and temperatures. In two dimensions (2D) the method is stable even in the presence of negative distribution functions, but on a smaller stability domain. The computational efficiency of the method compares favorably with classical algorithms for compressible flows, such as the

Unstructured lattice Boltzmann equation with memory

\lambda

Hybrid lattice Boltzmann method on overlapping grids

-scheme and the Lax--Wendroff scheme.

A comparison of numerical methods for non-Newtonian fluid flows in a sudden expansion

Starting from a second-order differential form of the semi-discrete Boltzmann equation, we construct a new finite-volume lattice Boltzmann equation on unstructured grids (ULBE). The new scheme (ULBE with memory) is demonstrated for the case of Taylor-vortex flow and shown to produce stable and accurate results with time-step more than an order of magnitude above the standard LBE stability threshold.

APPLICATIONS OF FINITE-DIFFERENCE LATTICE BOLTZMANN METHOD TO BREAKUP AND COALESCENCE IN MULTIPHASE FLOWS

In this work, a hybrid lattice Boltzmann method (HLBM) is proposed, where the standard lattice Boltzmann implementation based on the Bhatnagar-Gross-Krook (LBGK) approximation is combined together with an unstructured finite-volume lattice Boltzmann model. The method is constructed on an overlapping grid system, which allows the coexistence of a uniform lattice nodes spacing and a coordinate-free lattice structure. The natural adaptivity of the hybrid grid system makes the method particularly suitable to handle problems involving complex geometries. Moreover, the provided scheme ensures a high-accuracy solution near walls, given the capability of the unstructured submodel of achieving the desired level of refinement in a very flexible way. For these reasons, the HLBM represents a prospective tool for solving multiscale problems. The proposed method is here applied to the benchmark problem of a two-dimensional flow past a circular cylinder for a wide range of Reynolds numbers and its numerical performances are measured and compared with the standard LBGK ones.

An enhanced parallel version of kiva–3v, coupled with a 1d CFD code, and its use in general purpose engine applications

A numerical study on incompressible laminar flow in symmetric channel with sudden expansion is conducted. In this work, Newtonian and non-Newtonian fluids are considered, where non-Newtonian fluids are described by the power-law model. Three different computational methods are employed, namely a semi-implicit Chorin projection method (SICPM), an explicit algorithm based on fourth-order Runge–Kutta method (ERKM) and a Lattice Boltzmann method (LBM). The aim of the work is to investigate on the capabilities of the LBM for the solution of complex flows through the comparison with traditional computational methods. In the range of Reynolds number investigated, excellent agreement with the literature results is found. In particular, the LBM is found to be accurate in the prediction of the fluid flow behavior for the problem under consideration.

Multiscale Lattice Boltzmann Schemes: A Preliminary Application To Axial Turbomachine Flow Simulations

We present an application of the hybrid finite-difference Lattice-Boltzmann model, recently introduced by Lee and coworkers for the numerical simulation of complex multiphase flows.1–4 Three typical test-case applications are discussed, namely Rayleigh–Taylor instability, liquid droplet break-up and coalescence. The numerical simulations of the Rayleigh–Taylor instability confirm the capability of Lees method to reproduce literature results obtained with previous Lattice-Boltzmann models for non-ideal fluids. Simulations of two-dimensional droplet breakup reproduce the qualitative regimes observed in three-dimensional simulations, with mild quantitative deviations. Finally, the simulation of droplet coalescence highlights major departures from the three-dimensional picture.

Comparative environmental assessment of conventional, electric, hybrid, and fuel cell powertrains based on LCA

Numerical simulations of reactive flows are among the most computational demanding applications in the scientific computing world. KIVA-3V, a widely used computer program for CFD, specifically tailored to engine applications, had been deeply modified in order to improve accuracy and stability, while reducing computational time. The original methods included in KIVA to solve equations of fluid dynamics had been fully replaced by new solvers, with the aim of both improving performance and writing a fully parallel code. Almost every feature of original KIVA-3V has been partially or entirely rewritten, a full 1D code has been included and a strategy to link directly 3D zones with zero dimensional models has been developed. The result is a reliable program, noticeably faster than the original KIVA-3V in serial mode and obviously even more in parallel, capable of treating more complex cases and bigger grids, with the desired level of details where required.

Study of the impact on the spray shape stability and the combustion process of supply pressure fluctuations in CR-diesel injectors

Multiscale Lattice Boltzmann schemes for fluid dynamic applications are described and their efficiency is discussed in terms of accuracy and computational cost. A novel application to axial compressor flows is proposed. Conditions on periodic boundaries have been appropriately developed. Our preliminary results indicate that these schemes hold good potential for the simulation of fluid flows in turbomachines.