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Inlet boundary conditions at the supply opening play an important role in the accuracy and reliability of computational fluid dynamics (CFD) simulations for indoor airflow. A non-exhaustive overview of past CFD simulations of ventilation flow in generic enclosures indicates that uniform hypotheses of inlet boundary conditions are commonly used. However, due to thermal effects and a complex air supply system geometry, constant values of inlet airflow quantities can be insufficient for an accurate simulation of non-isothermal ventilation flow. In addition, this can lead to biased conclusions on the performance of turbulence models and other computational settings. To assess this issue, a well-documented experiment on non-isothermal mechanical ventilation with detailed information of inlet conditions from the literature is used in this study. Different turbulence models and inlet boundary conditions are validated, including seven steady Reynolds-averaged Navier-Stokes (RANS) models, six methods of imposing inlet air velocity, three methods of specifying air temperature, and a wide range of turbulence quantities. The parametric study demonstrates that in this particular case, i.e., cold air supply from a single round nozzle diffuser close to the ceiling, ω-based turbulence models perform better than the ε-based turbulence models. The impacts of different methods to specify inlet air temperature profile and turbulence quantities on the simulation results are not significant. However, if the inlet airflow direction is not taken into account appropriately, significant deviations are observed between CFD simulations and experimental data. • Detailed analyses of influence of inlet boundary conditions in CFD simulations. • Validation of RANS CFD simulations with measurement data from the literature. • ω-based turbulence models perform better than the ε-based turbulence models. • The inlet flow conditions can have a very strong effect on overall flow pattern. • Care should be taken in validation studies when inlet conditions are not known. [ABSTRACT FROM AUTHOR]

The paper presents a strategy to develop a fully transient numerical model of a heat transfer in building, using a transient CFD model of indoor air and a thermal envelope model, running in a co-simulation. The strategy relies on the utilization of RANS with a high-Returbulence model and a wall function, which enables to use a coarse computational mesh limiting the computational time. Since wall functions give invalid heat transfer coefficients in thermally developing indoor air regions and the exact location of these regions is not known in indoor spaces, a new air-wall heat transfer calibration procedure is adopted in the co-simulation. It is assumed that there is a uniform surface-averaged and time-dependent heat transfer coefficient per surface, extracted from the CFD solution. The calibration procedure is based on the near-wall mesh density adjustment to obtain surface-average heat transfer coefficients close to those calculated from empirical relationships for natural and forced convection. No local heat transfer coefficients are checked and no dimensionless wall distancesy+are monitored during the simulation. Due to the calibration it is ensured that the average air-wall heat transfer rate is accurate despite the use of wall functions. The capabilities of the model developed based on the strategy are presented in the case study: the analysis of the influence of wall thermal capacitance on indoor environment in a single well-ventilated room. [ABSTRACT FROM AUTHOR]

Abstract: We consider in this study the mixed convection airflow encountered in a 3D anisothermal cavity ventilated with supply and exhaust slots under stable thermal stratification. The flow in this cavity has been experimentally studied in the past (S. Mergui, Caractérisation expérimentale des écoulements d''air de convection naturelle et mixte dans une cavité fermée, thèse de l''Université de Poitiers, France, 1993) and was subject to a jet deflection and to a sudden change in the flow pattern between a general clockwise rotation and a counter-clockwise rotation when varying the inlet jet velocity. This phenomenon also exhibits a hysteresis effect depending on the way the velocity is changed, which made us to think that this flow bifurcation is of subcritical nature. Numerical studies have been yet devoted to this configuration, using RANS simulations or Large Eddy Simulation (LES), but this phenomenon has not been reported. So, we chose to numerically study this challenging flow with an LES approach associated with a subgrid diffusivity model previously developed for natural convection airflows. The comparison with the available experimental data and with other LES results using a classical dynamic model proves that the present LES not only correctly predicts the mean characteristics of the flow but is also able to correctly reproduce the flow bifurcation and the hysterisis effect. [Copyright &y& Elsevier]