Abstract Summary (Max 250 words)
We investigate mixing enhancement in Taylor-Couette flow using vertically asymmetric rough walls through experiments and direct numerical simulations. The inner cylinder features triangular ribs (heights δ = 0.2d, where dd is the gap width), creating direction-dependent shear: clockwise rotation exposes the steeper slope, counter-clockwise the gentler slope. Results show that asymmetric roughness significantly enhances momentum transfer compared to smooth walls. At high Taylor numbers (Ta up to 2.39×10⁷), clockwise rotation yields up to 15% greater torque—indicating enhanced mixing—than counter-clockwise rotation. DNS reveals three synergistic mechanisms: (i) increased convective angular velocity flux from stronger wall-bulk coupling; (ii) thinner boundary layers and elevated Reynolds stress indicating intensified turbulence; and (iii) dominant pressure force contribution on rough surfaces, maximized for clockwise rotation. At low Ta, directionality has negligible effect due to viscous dominance. These findings establish vertically asymmetric roughness as an effective passive strategy for tuning mixing in wall-bounded turbulence, with implications for chemical reactors and rotating machinery. The combined approach validates mechanistic insights for optimizing mixing through tailored wall topography.
