Improving virtual heat transfer description of developed and undeveloped annular gap flows at high Taylor numbers

Abstract Increased power densities of electric machines are, amongst other factors, related also to the increase of the rotors’ rotating velocities. These can be combined with axial flow to improve the heat transfer in the annular gap. The resulting high rotating and axial velocities are characterized with high Taylor ( Ta ) and Reynolds ( Re ) numbers. Such flow regimes are currently not yet thoroughly described. The reasons are in the complex interactions between the operating conditions, annular gap geometry and the conditions at the gap inlet, which affect the flow development in the gap. Each of these impacts varies between different electric machines, adding to the complexity of description. To address this, a numerical study based on 3D CFD simulations is performed. The study accounts for the impacts of the flow conditioning at the entrance to the annular gap and the possibility that the small scale turbulent structures might not be well resolved at high Ta numbers. Thus, different inflow configurations are applied using both RANS and LES models. The results are compared with available experimental and numerical data and provide a valuable insight into the requirements for reliable heat transfer description in the increasingly interesting flow conditions.