Entropy-based surface microprofiling for passive near-wall flow control

In this paper, embedded surface microchannels with varying geometrical profiles are developed and applied to drag reduction and near-wall flow control along a surface. Local slip-flow conditions and a temperature discontinuity are encountered within the microchannels along the flat surface. Diverging sections of each microchannel affect both the near-wall pressure and velocity distributions, thereby influencing the boundary layer separation and entropy production. This impact of surface microchannels is characterized with respect to entropy production of friction and thermal irreversibilities. The total entropy production is expressed in terms of the microchannel base and exit angles, depth and other geometrical parameters that characterize the microprofiled surface. Numerical results are presented for the optimized geometrical configuration of the microchannel profiles. Applications of the microprofiling technique are presented for near-wall flow control along a helicopter engine cooling bay surface.