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The effects of complex vortex structure on the internal flow and performance of a centrifugal fan with inclining symmetrical volute tongue were investigated by numerical simulations. The comparison between experimental results and numerical results on performance of a centrifugal fan is presented. To provide a quantitative analysis on the vortex structure in the internal flow of fan, Q criterion as a rule of vortex decision is implemented. Effects on vortex structure and X-velocity of the volute outlet are analyzed by modifying clearance and radius. It is analyzed to provide insight into the performance of the centrifugal fan. Special attention is devoted to the influence of the static pressure and efficiency of the fan by increasing radius of the volute tongue, changing tongue clearance and inclining volute tongue in this paper. The results also show that the static pressure of model B rises as much as 10.59 Pa and the efficiency can be improved by more than 4% compared with the original configuration due to the reduction of flow loss. It is further found that the static pressure efficiency increases with decreasing Q value distribution in the internal flow of the fan.

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Entropy generation in two-dimensional Rayleigh-Bénard convection at different Prandtl number (Pr) are investigated in the present paper by using the lattice Boltzmann Method. The major concern of the present paper is to explore the effects of Pr on the detailed information of local distributions of entropy generation in virtue of frictional and heat transfer irreversibility and the overall entropy generation in the whole flow field. The results of this work indicate that the significant viscous entropy generation rates (Su) gradually expand to bulk contributions of cavity with the increase of Pr, thermal entropy generation rates (S θ ) and total entropy generation rates (S) mainly concentrate in the steepest temperature gradient, the entropy generation in the flow is dominated by heat transfer irreversibility and for the same Rayleigh number, the amplitudes of Su, S θ and S decrease with increasing Pr. It is found that that the amplitudes of the horizontally averaged viscous entropy generation rates, thermal entropy generation rates and total entropy generation rates decrease with increasing Pr. The probability density functions of Su, S θ and S also indicate that a much thinner tail while the tails for large entropy generation values seem to fit the log-normal curve well with increasing Pr. The distribution and the departure from log-normality become robust with decreasing Pr.