Multiple input multiple output phononic subsurfaces for passive boundary layer transition delay

A method of controlling a flow comprising:

• providing a first interface surface and a second interface surface in a fluid flow along a flow structure, the fluid flow exhibiting turbulent or laminar flow characteristics, the first interface surface and the second interface surface arranged within the flow structure such that they each are exposed to one or more of a pressure gradient and a velocity gradient associated with complex motion of the fluid flow;
• and
• providing a subsurface feature extending from the interface surfaces, the subsurface feature comprising a phononic crystal or locally resonant metamaterial adapted to receive one or more of the pressure gradient or the velocity gradient from the fluid flow via the interface surfaces and to alter one or more of a phase and an amplitude of a plurality of frequency components of the fluid flow;
• and
• passively altering one or more of a phase or amplitude of a plurality of frequency components of the flow via the subsurface feature.