Abstract: For rotating machines or rotational energy harvesters, maintaining a constant shaft speed is essential to ensure stable energy transfer and to prevent component damage caused by sudden loading. In this study, a shear thickening non-Newtonian fluid is introduced into the clearance between the shaft and the sleeve. The regulating effect of this fluid on the rotational speed of the shaft is investigated through theoretical analysis and numerical simulation. The influence of fluid parameters—such as viscosity, consistency coefficient, rheological index, and yield stress—on the shaft speed is examined for various non-Newtonian fluid models, including Bingham fluid, power law fluid, Herschel-Bulkley fluid and Sisko fluid. The results indicate that under certain external load conditions, shear thickening non-Newtonian fluids can rapidly regulate on the rotational speed of the shaft.