Abstract
Kinematical and geometrical parameters of helical vortices winding in the same (right-handed) or opposite direction (left-handed) to the base Taylor-Couette-Poiseuile flow were studied at low Ta = R-1 d/v < 319 and Re = U-M d/v < 10.5 numbers. The inner cylinder (R-1 = 24.85 mm) rotated and the outer one (R-2 = 30.95 mm) was stationary. The parameters of helical vortices were obtained from flow visualizations and the wall shear rates were deduced from the electrodiffusion currents of three mass transfer probes flush mounted on the wall of the outer cylinder Kristiawan et al. [11] . The vector field of wall shear rate on the outer cylinder was reconstructed using a three-segment mass transfer probe. It is found that the axial component of the wall shear rate of the left-handed helices is greater than that of the right-handed helices. The motion of the flow structures near the outer wall was described by the velocity V resulting from the axial drifting velocity (U-D) and the azimuthal velocity W . It was shown that the axial velocity perceived by an observer or sensor fixed in the laboratory system U-OBS is composed of the drifting velocity U-D and the velocity due to the helix rotation U-Omega, known as Barber pole effect. New insight on the helical structures are revealed from studying the variations of different parameters such as the helix pitch p, the rotation rate and the observed angular velocity of the helices. (c) 2021 Elsevier Ltd. All rights reserved.