Modeling of torque resistance in laminar annular rotating flow with axial flow

The issue of electric power shortage in hypersonic aircraft has become increasingly prominent in recent years. The liquid-cooling ram air turbine power generation system, which uses fuel as the cooling medium, offers an effective solution. However, the high viscosity of the liquid causes significant rotating resistance torque, which reduces the energy conversion efficiency of the system. Moreover, the accurate prediction of the rotating resistance of the annulus in generator is limited by the applicability of existing expressions. To study the rotating torque characteristic in the stator-rotor gap of the liquid-cooling generator, the fundamental flow model, namely laminar annular rotating flow with axial flow (LARAF), is investigated in this paper. By drawing an analogy to transient parallel plane Couette flow, a torque expression applicable to LARAF is derived. Numerical simulations are performed to study the flow behavior in detail. A correction expression as function of the axial Reynolds number is established through statistical analysis. The predicted torque values are consistent with experimental results, with deviations remaining within ±7 %. A simplified method for deriving the torque expression of LARAF is developed by analogy method and good prediction accuracy is achieved through correction. This study proposes a novel perspective for understanding the torque characteristics of LARAF, laying a theoretical foundation for future research on annular rotating flow with axial flow in the presence of vortices or turbulence.