Steady motion of Bingham fluid between two concentric cylinders is investigated in this paper. The inner cylinder rotates at a constant speed with the outer cylinder stationary. There is a critical rotational speed Ωcr which exists due to the yield stress. If rotating speed exceeds the critical one, fluid stress within the whole gap is greater than the yield stress. Plug flow exists only for the rotating speed below Ωcr. The effect of the ratio between radii and Bingham number is discussed. The limiting case that two cylinders are very close is also discussed.Finally, the rheological parameters calibration formulas are derived.
Key Words : Bingham fluid, concentric cylinders, rheological parameters.