Valerio D’Alessandro

On the development of OpenFOAM solvers based on explicit and implicit high-order Runge–Kutta schemes for incompressible flows with heat transfer

Abstract Open-source CFD codes provide suitable environments for implementing and testing low-dissipative algorithms typically used to simulate turbulence. In this research work we developed CFD solvers for incompressible flows based on high-order explicit and diagonally implicit Runge–Kutta (RK) schemes for time integration. In particular, an iterated PISO-like procedure based on Rhie–Chow correction was used to handle pressure–velocity coupling within each implicit RK stage. For the explicit approach, a projected scheme was used to avoid the “checker-board” effect. The above-mentioned approaches were also extended to flow problems involving heat transfer. It is worth noting that the numerical technology available in the OpenFOAM library was used for space discretization. In this work, we additionally explore the reliability and effectiveness of the proposed implementations by computing several unsteady flow benchmarks; we also show that the numerical diffusion due to the time integration approach is completely canceled using the solution techniques proposed here.

An OpenFOAM Solver for Forced Convection Heat Transfer Adopting Diagonally Implicit Runge–Kutta Schemes

Nowadays open-source CFD codes provide suitable environments for the implementation and testing low-dissipative algorithms typically used for turbulence simulation. Therefore in this research work, we have developed a CFD solver for incompressible fluid flow and forced convection heat transfer based on high-order diagonally implicit Runge–Kutta (RK) schemes for time integration. In particular, an iterated PISO-like procedure based on Rhie–Chow correction was used for handling pressure–velocity coupling within each RK stage. It is worth emphasizing that for space discretization, the numerical technology available within the well-known OpenFOAM library was used. The first aim of this work was to explore the reliability and effectiveness of OpenFOAM library for convective heat transfer problems using high-fidelity numerics. This is a point of interest since we cannot find similar papers in the available literature. The accuracy of the considered algorithm was evaluated studying several flow benchmarks. Hence, we also provide a further contribution to the literature involving forced convection heat transfer around bluff bodies at low Reynolds numbers. Lastly, this paper is only a first step toward turbulent heat transfer simulation in complex configurations by means of DNS/LES techniques.

On the improvement of computational performance of a vapor-liquid equilibria solver for mixtures

This work deals the computational performance improvement of vapor–liquid equilibria solver for fluids mixtures. The code here developed is based on the chemical potential equality (expressed in terms of fugacity) and implements Soave–Redlich–Kwong and Peng–Robinson equations of state with classical van der Waals mixing rules. To reduce the bulk of the computational effort required by the solver we propose the following approaches: (i) exploit high-order methods for the solution of Rachford–Rice equation; (ii) develop an efficient programming methodology for the sub-routines devoted to the fugacity coefficients computation in order to reduce their overall impact on the CPU-time exploiting the parallelism at CPU level, i.e. CPU pipelining, and cache blocking. In this paper we have carefully evaluated the effectiveness of the aforementioned approaches performing a suite of computations of the equilibrium properties of several literature mixtures. The pros and cons of the strategies here suggested are outlined and discussed.

Study of the flow field past dimpled aerodynamic surfaces: numerical simulation and experimental verification

This work presents the study of the flow field past of dimpled laminar airfoil. Fluid dynamic behaviour of these elements has been not still deeply studied in the scientific community. Therefore Computational Fluid-Dynamics (CFD) is here used to analyze the flow field induced by dimples on the NACA 64-014A laminar airfoil at Re = 1.75 105 at α = 0°. Reynolds Averaged Navier–Stokes (RANS) equations and Large-Eddy Simulations (LES) were compared with wind tunnel measurements in order to evaluate their effectiveness in the modeling this kind of flow field. LES equations were solved using a specifically developed OpenFOAM solver adopting an L–stable Singly Diagonally Implicit Runge–Kutta (SDIRK) technique with an iterated PISO-like procedure for handling pressure-velocity coupling within each RK stage. Dynamic Smagorinsky subgrid model was employed. LES results provided good agreement with experimental data, while RANS equations closed with approach overstimates laminar separation bubble (LSB) extension of dimpled and un–dimpled configurations. Moreover, through skin friction coefficient analysis, we found a different representation of the turbulent zone between the numerical models; indeed, with RANS model LSB seems to be divided in two different parts, meanwhile LES model shows a LSB global reduction.

A Solar Chimney for renewable energy production: thermo-fluid dynamic optimization by CFD analyses

This paper analyzes the performance of a solar tower designed for renewable energy production. The Solar Chimney Power Plant (SCPP) involves technology that converts solar energy by means of three basic components: a large circular solar collector, a high tower in the center of the collector and a turbine generator inside the chimney. SCPPs are characterized by long term operational life, low maintenance costs, zero use of fuels, no use of water and no emissions of greenhouse gases. The main problem of this technology is the low energy global conversion coefficient due to the presence of four conversions: solar radiation > thermal energy > kinetic energy > mechanical energy > electric energy. This paper defines its starting point from the well known power plant of Manzanares in order to calibrate a numerical model based on finite volumes. Following that, a solar tower with reduced dimensions was designed and an analysis on various geometric parameters was conducted: on the inlet section, on the collector slope, and on the fillet radius among the SUPP sections. Once the optimal solution was identified, a curved deflectors able to induce a flow swirl along the vertical tower axis was designed.

A Spalart–Allmaras local correlation–based transition model for Thermo–fuid dynamics

The study of innovative energy systems often involves complex fluid flows problems and the Computational Fluid-Dynamics (CFD) is one of the main tools of analysis. It is important to put in evidence that in several energy systems the flow field experiences the laminar-to-turbulent transition. Direct Numerical Simulations (DNS) or Large Eddy Simulation (LES) are able to predict the flow transition but they are still inapplicable to the study of real problems due to the significant computational resources requirements. Differently standard Reynolds Averaged Navier Stokes (RANS) approaches are not always reliable since they assume a fully turbulent regime. In order to overcome this drawback in the recent years some locally formulated transition RANS models have been developed. In this work, we present a local correlation–based transition approach adding two equations that control the laminar-toturbulent transition process –γ and – to the well–known Spalart–Allmaras (SA) turbulence model. The new model was implemented within OpenFOAM code. The energy equation is also implemented in order to evaluate the model performance in thermal–fluid dynamics applications. In all the considered cases a very good agreement between numerical and experimental data was observed.