Ocean Engineering 245 (2022) 110454 0029-8018/© 2021 Published by Elsevier Ltd. Experimental hydrodynamic investigations on the effectiveness of inverted fag-based piezoelectric energy harvester in the wake of bluff body M. Umair a, 1 , U. Latif a, b, 1 , E. Uddin a, * , A. Abdelkef c a Department of Mechanical Engineering, School of Mechanical and Manufacturing Engineering (SMME), National University of Sciences and Technology (NUST), H-12, Islamabad, Pakistan b Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC, 27708, USA c Department of Mechanical and Aerospace Engineering, New Mexico State University, Las Cruces, NM, 88003, USA A R T I C L E INFO Keywords: Inverted fag Piezoelectric energy harvesting Hydrodynamic analysis Bending rigidity Experimental measurements ABSTRACT The fapping motion and energy harvesting performance of an inverted fag in the wake of a bluff body are experimentally studied. The experimental measurements are carried out by changing the bending rigidity, streamwise gap (which represents the distance from the bluff body to the tip of the fag), and Reynolds number to explore their impact on the fapping dynamics and power generated by the piezoelectric fag. The optimal values of the Reynolds number, bending rigidity, and streamwise gap are determined based on the power generated. Variation in the fapping modes ranging from continuous to defected mode is observed. The results show that the inverted fag having a high peak-to-peak amplitude is preferred for piezoelectric energy harvesting as it produces high strain energy. It is also demonstrated that the vortices shed by the upstream bluff body have a strong effect on the fapping amplitude of the downstream inverted fag. This research would help in determining the most effective streamwise position of the inverted fag behind the bluff body and bending rigidity for generating voltage at low Reynolds numbers. 1. Introduction Due to the limited resources of fossil fuels, the increase in demand, and their environmental impacts, the search for sustainable energy sources rises and harvesting energy from renewable resources has been increased (Kaygusuz, 2012; Panwar et al., 2011). Piezoelectric-based energy harvesting systems have gained attention as they are useful in applications like strain gauge and pressure transducer (Blair and Lacy, 1993). Indeed, attached piezoelectric patches to fexible structures can convert the strain energy caused by its deformation into electrical en- ergy (Latif et al., 2020a; Asfandyar Arshad Usman Latif EUAA, 2020; Usman Latif Emad Uddin, 2020). In nature, the motion of fsh in water behaves like a fexible structure in the fuid fow. This movement affects the motion of other fsh behind it or bluff body because of their vorticity effect (Uddin et al., 2015; BEAL et al., 2006). In addition to the possible interaction between fexible structures and bluff bodies like column of offshore structures or riser pipes (U and Shah, 2016), numerous research studies have been carried out on self-excited oscillations (Eugeni et al., 2017; Yang et al., 2019) as they can be transferred into piezoelectric patches which convert them into electrical energy (Abdelkef, 2016). In recent years, most of the research has been done on the fapping dynamics of fexible structures in a fuid fow and the possibility of energy harvesting from these vibratory motions (Latif et al., 2018; Elahi et al., 2020). To mimic this phenom- enon, a thin fexible sheet in fuid fow can cause deformations in the piezoelectric sheet and hence can harvest energy. Airfow over a clam- ped piezoelectric fag without a bluff body when reaches a critical ve- locity causes a futter and hence harvests energy from oscillatory piezoelectric patches (Eugeni et al., 2020). The fexible fag can have two confgurations. One having clamped leading edge and free trailing edge, termed as a conventional fag (Latif et al., 2020b), while the other having a free leading edge and clamped trailing edge and is termed as an inverted fag (Kim et al., 2017). Both can fap in a uniform fow or behind the bluff body and the latter one was demonstrated to be more effcient (Michelin and Doar´ e, 2013). Various confgurations with conventional and inverted fags were used by several researchers to induce large oscillations and fapping amplitudes like a tandem, side by side, and multiple fags in diamond or * Corresponding author. E-mail address: emaduddin@smme.nust.edu.pk (E. Uddin). 1 Equal contribution by both leading authors. Contents lists available at ScienceDirect Ocean Engineering journal homepage: www.elsevier.com/locate/oceaneng https://doi.org/10.1016/j.oceaneng.2021.110454 Received 19 August 2021; Received in revised form 22 December 2021; Accepted 23 December 2021