Browsing by Author "Serra, Nuno"
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- ESIMPLE, a new pressure-velocity coupling algorithm for built-environment CFD simulationsPublication . Serra, Nuno; Semião, ViriatoBuilt environments are major energy consumers and, therefore, tools supporting their efficient design and guaranteeing thermal comfort and indoor air quality are a key factor for energy, environmental sustainability and healthiness. This has been particularly stressed recently by the need to understand the phenomenon of transport of pollutants and/or pathogens leading to exhalation of droplets and aerosols in built environments from people potentially contaminated with the new coronaviruses. In the pursuance of such objectives, CFD procedures have been widely used as prediction tools due to its ability and flexibility in capturing the main features of built environment flows. On the other hand, CFD methods are supported by complex and timeconsuming calculation procedures, especially when used to predict heat and mass transport phenomena in built environment. A possible strategy to reduce computational time is the optimization of the pressure-velocity coupling. An extension of the SIMPLE algorithm (ESIMPLE) is proposed, and its performance compared with the well stablished algorithms, SIMPLE, PISO, SIMPLEC and LIMPO. For that, three test case scenarios are simulated: i) a cubical room (1 m3) with heated floor; ii) a small-scale room, with an occupant, mimicking an office room; and iii) a real-scale office room with an occupant. For the worst scenario, ESIMPLE yielded similar CPU-time required for convergence, and for the best scenario, a three times faster convergence rate was attained. Simultaneously, this newly proposed coupling scheme algorithm, yielded a lower number of iteration steps required for convergence, in 6 of the 9 simulated cases.
- Revisiting RANS turbulence modelling used in built-environment CFD simulationsPublication . Serra, NunoThe strong commitment of European Union (EU) to energy efficiency and the increasing energy prices will put pressure on the building sector to find solutions that are simultaneously very low-level or nearly zero energy-consuming, efficient, thermally comfortable and disease free. In the pursuit of such solutions, Computational Fluid Dynamics (CFD) has been used, with great success, in predicting and optimizing built-environment flows. Nonetheless, it is known that the choice of the turbulence model and the way in which it treats the near wall region, influences the quality of the yielded results. A set of experimental three-dimensional particle image velocimetry (3D PIV) data is used to assess the predictive ability of six turbulence models, commonly used in built-environment simulations, together with two new variants of the turbulence model k- epsilon -v2 -f. The phenomena variables, inside a 1:30 lab-scale room, with an emulated occupant were computed for two different ventilation strategies, displacement and mixing. Only the k-epsilon RNG VisEff and the original 'code-friendly' variant of the k -epsilon -v2 -f (LKM) coherently described the two simulated flows. Furthermore, it was not unequivocal that obeying the dimensionless wall distance (Y+) less than 1 rule, for the first grid node, guaranteed the enhancement of the computed results. The integration of the Standard Wall Functions (SWF) with the k- epsilon -v2 -f (LKM) turbulence model proved to yield more accurate and less grid-dependent results than the stand-alone k -epsilon -v2 -f (LKM) model, showing, simultaneously, a predictive ability similar to that of the k-epsilon RNG VisEff model, despite the lower computational complexity of the latter.
- UNIPARTNER: empresa prestadora de serviços do KOHAPublication . Serra, NunoComunicação Painel 4 | Implementação do sistema no mercado