A multi-modal bidirectional galloping energy harvester with mode transition for alternating wind directions

This study proposes a multi-modal bidirectional galloping energy harvester, enabled by mode transition mechanism (MBEH-MT), to address the wind direction limitation of conventional galloping-based piezoelectric wind energy harvesters. The MBEH-MT features a three-bluff-body configuration connected by symmetric cantilever beams, allowing energy harvesting in both positive and negative wind directions. A continuous coupled mathematical model is developed based on Hamilton's principle and Euler–Bernoulli beam theory, with modal reduction via the Galerkin method. The first three modes are investigated through the analysis of mode shapes and natural frequencies. The theoretical results are validated through a series of wind tunnel tests, which demonstrates that the third mode is dominant under the positive wind direction, whereas mode transition phenomenon from the first mode to the second mode occurs under the negative wind direction. The results imply that the mode transition characteristics are beneficial for significantly enhancing energy harvesting efficiency through the adaptation of vibration modes under alternating negative wind speeds. The experimental results indicate that the MBEH-MT is feasible for achieving bidirectional wind energy harvesting. Moreover, a 112.4% increase in output power is achieved, compared to the conventional galloping energy harvester constructed with a single cantilever beam, reaching an overall average output power of 19.72 μW. The outstanding performance and bidirectional wind adaptability of the proposed system highlight its potential for powering low-consumption devices under alternating wind directions, such as tunnel entrances and exhaust ducts.