EFFECT OF ATTACHMENT FOR BLUFF BODY SURFACE ON PIEZOELECTRIC ENERGY HARVESTER PERFORMANCE IN LOW VELOCITY WATER FLOW

Low velocity water flow energy is an important complement to renewable energy and the piezoelectric energy harvesters developed by using this energy have shown excellent performance in flow fields. The energy conversion of piezoelectric energy harvesters can be affected by the added attachments on bluff body surface. Therefore, the output characteristics of the piezoelectric energy harvester are investigated by varying the shape, the convexity height and the concavity depth of the attachment. Mechanical governing equation of the piezoelectric energy harvester is developed by using the extended Hamilton’s principle, the electric field-displacement governing equation is obtained by applying Gauss law, the quasi-steady-state assumption is employed to calculate the hydrodynamic force and moment of galloping, and then the electromechanical coupling piecewise distributed parameter model of the piezoelectric energy harvester is established. The displacement of the cantilever beam is discrete by Galerkin procedure, and the governing equations are decoupled on this basis to obtain the approximate solution of harvester output power and bluff body displacement. Experimental solutions of the output power are obtained by water channel experiment and the accuracy of model is further verified. The results showed that at the flow velocity of 0.51 m/s, the RMS power of the piezoelectric energy harvester wrapped ellipsoidal attachment with −2 mm convexity is 1.411 mW, an increase of 69.88% compared to the elliptic cylinder without attachment, and the amplitude of cantilever beam is 3.07 mm when the bluff body is equipped on the cylindrical attachment with 6 mm convexity, a reduction of 84.83% compared to the one without the attachment. The numerical simulation results show that the application of the convex and concave attachment for 2 mm increases the pressure differential across bluff body, which intensifies vibration, it also affects the size and strength of shedding vortices from both sides of the bluff body.