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Torque measurements for spherical Couette flow of non-Newtonian fluids are presented together with flow characteristics in a region of low rotational Reynalds number up to an onset of hydrodynamic instability. The spherical flow configuration in the present study is such that the inner sphere is rotated while the outer sphere is kept stationary. The rotational torque induced by shear stress on the inner sphere surface is measured for dilute, aqueous polymer solutions (PEO: Polyethylene oxide and PAA: Polyacrylamide) of various concentrations. The experimental results show that before the onset of hydrodynamic instability the torque characteristics are higher than those estimated for linear azimuthal velocity profile in the spherical gap. It is shown consequently that the measured torque can be well described by the integral correlation formula that considers the azimuthal nonlinear velocity profile and involves the generalized Reynolds number. The critical Reynolds number associated with the onset of the hydrodynamic instability (laminar transition) is much lower than that estimated from Newtonian correlational equation (modified by the generalized Reynolds number) and is strongly dependent upon the concentration of the PEO and PAA polymer solutions.

Spherical Couette Flow of Non-Newtonian Fluid in Low Rotational Reynolds Number Region