An experimental study of sustainable drag reduction in Taylor-Couette flow*

Researchers have shown that superhydrophobic (SH) surfaces can decrease frictional drag force. In our study, patterned SH surfaces were used in laminar and turbulent flow of a bespoke Taylor-Couette apparatus to comprehend their drag reduction mechanism. Our Taylor-Couette cell was mounted on a rheometer device that could measure the torque on the inner rotor as a function of rotational speed. We applied SH coatings on an inner cylinder to evaluate the drag reduction performance of various coatings in different flow regimes and calculate the effective slip length. We also studied drag reduction in patterned structures on the cylinder, and here it was revealed that triangular-shaped riblets achieved effective surface drag reduction. Furthermore, we examined combined surface modifications, SH coating and V-grooves in the Taylor-Couette flow. The performance of these surfaces was compared in terms of different dimensionless parameters; their surface roughness, the riblets sharpness and the Reynolds number. Our experimental results showed a reduction in measured torque of up to 45%. Also, durability tests indicated that our designed surfaces could maintain their hydrophobicity over repeated tests.