The effect of smaller turbulent motions on heat transfer in the annular gap flow of flywheel

• Small scale Görtler vortices are found in the annular gap flow of flywheel with PANS model.
• There is a larger temperature gradient at Görtler vortices region.
• There are two temperature mixing processes at the boundaries of a pair of Taylor vortices.

The forced convective heat transfer in the gap of a flywheel is affects the safety of reactor coolant pump (RCP), such as the operation temperature limit of the bearing, therefore it is necessary to analyze the heat transfer in the annular gap flow of a flywheel. The current study provides evidence that the convective heat transfer depends on the flow structure. When the Taylor number of this flow is about 1E12, the flow structure has a special pattern likes Herringbone near the wall, and consists of many smaller Görtler vortices. Although the earliest experimental studies found the Görtler vortex with laser-induced fluorescence (LIF), these vortices are difficult to study by numerical analysis with direct numerical simulation (DNS) or the large eddy simulation (LES), and the Reynolds-averaged Navier–Stocks (RANS) cannot capture the smaller scale vortices in the wall boundary layers with overestimated eddy viscosity. In this paper, we adopt the partially-averaged Navier–Stokes (PANS) model to observe the smaller turbulent motions in the annular gap flow of a flywheel, and analyze the effect of Görtler vortices on convective heat transfer. Compared with k–ε, PANS simulation suggests that there are larger temperature gradients at the Görtler vortices region, and two temperature mixing processes occur at the boundaries of a pair of Taylor vortices.