Drag decomposition of laminar channel flows developing over convergent–divergent riblets

Convergent–divergent (C–D) riblets are known to induce large-scale secondary flow motion in laminar that may point their potential for separation control and heat transfer enhancement. In this paper, a fully-developed pressure-driven channel with C–D is studied numerically. The effects of Reynolds number, riblet wavelength cross-sectional shape on the drag characteristics investigated. An exact expression coefficient derived based balance kinetic energy principle rough-wall channel. Furthermore, triple decomposition technique used identify contribution production from mean velocity field, small- dispersive field. Our results show normalized increment starts rise when begins alter field across span as number height (ReH) increases above 100, behavior which very different developing over homogeneous roughness found remain constant up much greater due an absence flow. It produced by predominantly caused wall-normal gradient streamwise velocity. addition, while small-scale at ReH≤100, rapidly becomes dominant ReH exceeds 400. also observed scales Λ, its swirling strength peaks around Λ=1.25H, accompanied maxima ReH≥400. Finally, among three (rectangular, triangular sinusoidal) examined here, pattern produce similar other two shapes but less penalty.