Hydrodynamic metamaterials for flow manipulation: Functions and prospects

As an emerging branch in the area of flow control, hydrodynamic metamaterials have received considerable attention because of their novel flow control capabilities. In this review, we present prominent studies on hydrodynamic metamaterials in porous media, non-porous media, creeping flows, and non-creeping flows from several perspectives. In particular, for hydrodynamic cloaking metamaterials, we unify the descriptive form of transformation hydrodynamics for hydrodynamic metamaterials in porous and non-porous media by the hydrodynamic governing equations. Finally, we summarize and outlook the current shortcomings and challenges of current hydrodynamic metamaterials and propose possible future research directions, especially for microfluidics, exotic fluids, hydrodynamic cloaking in high Reynolds numbers, and turbulence.