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The lattice Boltzmann modeling of immiscible multiphase flows needs to be further validated, especially when density variation occurs between the different flow phases. From this perspective, the goal of this research is to introduce the multiple-relaxation-time operator into a lattice Boltzmann model in order to improve its numerical stability in the presence of large density and viscosity ratios. Essentially, this research shows that the introduction of this operator greatly improves the numerical stability of the approach compared to the original single-relaxation-time collision operator. In many lattice Boltzmann research studies, multiphase lattice Boltzmann methods are validated using a reduced number of test cases, and unsteady flow test cases are frequently omitted before much more complex flow configurations are simulated. In this context, several test cases are proposed to evaluate the behavior of a lattice Boltzmann method for simulating immiscible multiphase flows with high density and viscosity ratios. These are: (1) two-phase Couette flow; (2) three-phase Laplace law; (3) three-phase Zalesak disk; (4) two-phase flow between oscillating plates; (5) two-phase capillary wave; and (6) the two-phase oscillating cylindrical bubble. The first two involve a steady regime, and the remaining four an unsteady regime.

The combined effects of noise and temperature on environmental perception and acceptability were studied on 18 lightly clothed subjects (0.6 clo), individually exposed for 2 h in a climatic chamber. Three homogeneous climatic conditions were chosen (air temperature at 18, 24 or 30 degrees C, air velocity =0.1 m/s). For each of them, three different noise levels were continuously maintained (35, 60, 75 dBA, recorded fan noise). The 18 subjects were divided into three groups and each group experienced only one single thermal condition, at each level of noise, during three different experimental sessions. Subjective answers about perception and comfort were obtained at t = 30 and 120 min. Main results indicate that acoustic perception decreases when thermal environment is far from thermoneutrality. Although the combined effects of noise and temperature did not influence the physiological data, our results show that whatever the ambient temperature, thermal unpleasantness is higher when noise level increases. Finally, equivalence between acoustic and thermal sensations is proposed for short-term exposure (1 degree C = 2.6 dBA) and for steady state (1 degrees C = 2.9 dBA). In conclusion, this study strongly suggests that interactions between environmental components do exist, right from perceptual level, and might explain some combined effects on cognitive performance.

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