Flow energy harvesting devices and systems

A flow energy harvesting device comprising:

• a flextensional member comprising:
• a frame defining an interior cavity;
• and
• a cantilever extending outward from the frame, the cantilever comprising a non-piezoelectric material;
• and
• a stack of piezoelectric elements housed in the interior cavity of the frame.

A method of generating power down hole in a wellbore having a formation wall and a pipe spaced apart from the formation wall by an annular region, the method comprising:

• positioning a flow energy harvesting system in the annular region, the flow energy harvesting system comprising:
• a plurality of nozzle-diffusers defining a plurality of spline-shaped flow channels, each spline-shaped flow channel comprising a converging portion, a diverging portion, and a constriction section between the converging and diverging portions;
• and
• a plurality of flow energy harvesting devices in the plurality of spline-shaped flow channels, each flow energy harvesting device comprising:
• a flextensional member having a frame and a cantilever extending outward from the frame, the cantilever comprising a non-piezoelectric material;
• and
• a stack of piezoelectric elements housed in an interior cavity defined in the frame,
• wherein, for each of the plurality of flow energy harvesting devices, the frame of the flextensional member is in the converging portion of one of the spline-shaped flow channels and at least a portion of the cantilever of the flextensional member is in the constriction section of the one of the spline-shaped flow channels, and
• wherein, for each of the plurality of flow energy harvesting devices, the frame is configured to deform and elongate the stack of piezoelectric elements to generate a current based on the piezoelectric effect when a fluid flows through the annular region and the plurality of spline-shaped flow channels and generates unbalanced forces on the cantilever due to aeroelastic flutter.