Mixed convection between rotating sphere and concentric cubical enclosure

Abstract

This paper presents numerical investigations of the mix convection between a rotating inner sphere and a concentric cubical enclosure, using the recently developed immersed boundary-simplified lattice Boltzmann method. The validity of the method has been established through benchmark tests, and a grid independence study is also carried out to ensure the accuracy of the conveyed results. Various factors that may influence the mixed convection system, such as the rotational direction, Rayleigh number, and rotational Reynolds number, are considered in the present study. Three representative rotational axes, namely, the vertical, the horizontal, and the diagonal axes, are selected. The Rayleigh number spans from 104 to 106, which covers the transition range from a conduction-dominated system to a convection-dominated one. Moreover, the rotational Reynolds number varies from 0 to 300. Distinct flow patterns, global heat transfer behavior, and the heat transfer rates on cubic walls are studied to reveal the characteristics of this problem. It is found that the rotationality of the inner sphere would increase the global heat transfer rate of the system and the rotating motion would stimulate heat transfer in the radial direction of the rotational axis while suppressing the thermal expansion in the axial direction.