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;
• passively altering one or more of a phase or amplitude of a plurality of frequency components of the flow via the subsurface feature, and
• vibrating the set of interface surfaces at a phase and amplitude of a plurality of frequency components of the flow, wherein
• the set of interface surfaces are physically coupled to one or more masses in the subsurface feature, and the masses are tuned such that the interface surfaces vibrate at a plurality of frequencies in response to the pressure and/or velocity gradients of the fluid flow.

A system for reducing skin friction of a surface using multi-input, multi-output phononic subsurfaces for passive boundary layer transition delay comprising:

• a first interface surface and a second interface surface that respond to at least one of a pressure gradient or a velocity gradient in a wave of a turbulent fluid flow or a laminar fluid flow, the pressure gradient or the velocity gradient associated with complex motion of the fluid flow exhibiting a plurality of frequencies exerted on one or more of the interface surfaces;
• and
• a subsurface feature comprising a plurality of masses extending from the interface surfaces, the subsurface feature adapted to receive one or more of the pressure gradient or the velocity gradient from the fluid flow via the interface surfaces and to passively alter one or more of a phase and an amplitude of a plurality of frequency components of the fluid flow, wherein:
• the plurality of masses comprises:
• a first set of masses comprising a first mass, and
• a second set of masses comprising a second mass, and
• the first set and the second set are arranged in an alternating pattern and connected with one another in series via a plurality of flexible segment beams.