To study the instability of flow and heat transfer within the rotation frame, a rotating cavity with air axial throughflow was studied numerically and efforts were focused upon the flow structure evolution with the increase of Rayleigh number. The cavity can be divided into two typical zones: the Rayleigh_Benard-like convection zone occupying the upper cavity and the forced convection zone down under. These two zones interact with each other via the exchange of mass, momentum and energy. Numerical analysis indicated that, for a fixed inlet Reynolds number, there always exists a critical Rayleigh number Rac, below which the flow is stable and over which the flow becomes unstable and time-dependent. Among all the forces in momentum equations, the centrifugal induced buoyancy force was found to be the key factor leading to instability, while the Coriolis force pays its contribution to instability by inducing its occurrence earlier and the flow structure more complicated though it may not lead to instable by itself. The instability originated in the upper R-B-like convection zone develops into the whole region with the increase of Rayleigh number. For the heat transfer, the characteristic distribution of local Nur along the disk surface is remarkably different before and right after the occurrence of instability due to flow structure variation though the averaged Nuav varies slightly. It was found that the heat transfer, however, does experience a sudden increase when the flow instability develops further with Ra increase.

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