Flow of Power-Law Fluids Past a Rotating Cylinder at High Reynolds Numbers

In this study, a rotating cylinder is placed in a stream of shear-thinning fluids, flowing with a uniform velocity. Detailed investigations are performed for the following range of conditions: Reynolds number 100 <= Re <= 500, power-law index 0.2 <= n <= 1 and rotational velocity 0 <= alpha <= 5. Flow transitions are observed from steady to unsteady at critical values of the Reynolds number, the rotational velocity, and the power-law index. Critical values of the Reynolds number Re-c have been obtained for varying levels of the rotational velocity, and the power-law index. Re-c varies nonmonotonically with the rotational velocity. At a particular Reynolds number, an increase of the rotational velocity acts as a vortex suppression technique. For shear-thinning fluids considered here, the vortex suppression occurs at a larger value of the critical rotational velocity alpha(c), relative to Newtonian fluids. For the unsteady flow, the lift coefficient versus time curve exhibits oscillatory behavior, and this has been used to delineate the flow regime as steady or unsteady flow. For unsteady flow regimes, both the amplitude of the lift coefficient and the Strouhal number increase with increasing Reynolds numbers. The results presented in this work for such high Reynolds numbers elucidate the possible complex interplay between the kinematic and rheological parameters of non-Newtonian fluids. This investigation also complements the currently available low Reynolds number results up to similar to Re = 140.

Automated summary

In this study, experiments were conducted to observe flow transitions of a rotating cylinder in shear-thinning fluids under different conditions, revealing critical values for Reynolds number, rotational velocity, and power-law index, as well as their nonmonotonic relationships. Additionally, it was found that increasing rotational velocity at a specific Reynolds number can suppress vortex formation in shear-thinning fluids, and the lift coefficient oscillates in unsteady flow regimes, with both amplitude and Strouhal number increasing with Reynolds number. The results highlight the complex interplay between kinematic and rheological parameters in non-Newtonian fluids at high Reynolds numbers, complementing existing low Reynolds number data.