## 5 Conclusions  
In conclusion, the piezoelectric VIV harvester from this research implements a T-shaped design with a fixed bluff splitter body attached to a cantilever PVEH plate, in order to increase the aspect ratio for better flow separation and to further improve the quality of vortex generated. It is shown that with the presence of a bluff splitter body, the aspect ratio of the structure increases to a value of 15 henceforth the vortex generated is more visible and well defined compared to a single PVEH plate. The results show that with the same model design and a constant supply of wind flow, variance in wind speed does not affect the vortex formation length, but it will change the vortex frequency and fluctuating lift force acting on the model. It is shown from the results discussed above that, 19 m/s wind speed yields vortex frequency of 75.758 Hz, nearest to the structural modal's natural frequency with \(-1.48\%\) differences. Hence the structural model undergoes resonance, producing the highest RMS VIV amplitude of 1.26 mm with a 49.76%-times increment when compared to 20 m/s case. This research deduced that a model's VIV frequency tends to lock-in to the vortex frequency and the contribution of resultant vortex frequency is larger than the fluctuating lift force in improving the vibrational amplitude. In order to achieve significantly larger vibrational amplitude, it is more important to synchronize the vortex frequency with the model's natural frequency rather than only increase the wind speed to get a larger lift force which does not guarantee a larger amplitude accomplishment. In terms of experimental electrical performance, it is also concluded that when vibrational frequency is nearer to the structure's natural frequency, the voltage output is higher than the non-synchronized ones. When coupled with the optimum impedance value, the PVEH plate produces the largest normalized power of \(13.44\) mW/cm\({}^{3}\)g\({}^{2}\) when the vibrating frequency of 75.758 Hz resonates with the PVEH plate's fundamental natural frequency. Hence, it is proven that by installing the designed T-shaped VIV energy harvester at an optimum forced wind speed condition coupled with optimum load, a significant amount of power is able to be induced.  
It is proven above that matching natural frequency to the vortex frequency enables generation of the maximum voltage, therefore in future efforts to reduce the overall structure's natural frequency could be focused on lowering the wind speed required to achieve the resonant frequency, thus improving performance when installed in conventional exhaust air cooling towers that generate lower exhaust air velocity. A prototype could also be fabricated to conduct wind tunnel and on-site tests in the future to further justify the practicality of the VIV harvesters in real life application. Finally, more factors that will affect the VIV performance such as the aspect ratios of the model, design of bluff splitter body, the model arrays and many more will be investigated and compiled in the future.  
The authors wish to acknowledge the financial support and advice given by Postgraduate Research Grant (PG005-2015A), Fundamental Research Grant Scheme (FP010-2014A), Advanced Shock and Vibration Research (ASVR) Group of University of Malaya and other project collaborators. The authors also wish to thank [PERSON] and [PERSON] for helping the experimental measurements.  
This study was initiated and designed by [PERSON]. [PERSON] set-up experimental platform and conducted the experiments. [PERSON] and [PERSON] were responsible in numerical simulations. All authors contributed in analyzing the simulation and experimental results. [PERSON] and [PERSON] wrote the paper and all authors contributed in revising the paper.  
The authors declare no conflict of interest.