Experimental and numerical investigation of frictional loss and empirical correlation in Taylor–Couette–Poiseuille flow for a high-speed PMSM with an H2O2-flooded gap

A high-speed permanent magnet synchronous motor (PMSM) used in rocket propellant feed systems generates complex Taylor–Couette–Poiseuille (TCP) flow due to the H 2 O 2 -flooded gap and high rotational speeds, complicating the analysis of motor friction loss. To address this, a three-dimensional CFD model based on the RNG k–ε turbulence model with Enhanced Wall Treatment was established. The model was validated against drag method experiments on two prototypes (rotor diameters: 26.5 mm and 40 mm), achieving agreement within 7% across the full speed range. Systematic parametric simulations identified rotational speed as the dominant factor influencing friction loss, with a power-law relationship of P f ∝ n 2.85 , and rotor-side surface roughness was found to be the most influential controllable design parameter (+ 26.6% over the studied R a range). A dual-variable empirical correlation for the skin friction coefficient ( C f ) was derived, incorporating both the rotational Reynolds number ( Re gap ) and the axial Reynolds number ( Re ax ). This correlation was validated to predict friction loss within 7% of experimental measurements across rotational speeds of 10,000–40,000 rpm and axial Reynolds numbers up to 5000. The sensitivity ranking and empirical correlation provide quantitative design guidance for reducing friction in high-speed liquid-filled PMSMs.