Performance Improvement and Similarity Analysis for Torsional Galloping Based Turbine

This paper addresses the innovative turbine for hydrokinetic energy extraction proposed by (Fernandes and Armandei, 2014). This turbine harvests energy via torsional galloping. The turbine consists of a rectangular flat plate located vertically initially aligned with the water current and connected with a torsional spring. By changing the axis position, some experimental tests are conducted to assess the improvements on the performance of the turbine. It is observed that the optimal position for the elastic axis happens when the axis is located at 0.75 of the chord length from the leading edge. This is in accordance with the ideal axis position obtained from the Theodorsen theory reported in a PhD thesis (Armandei, 2013). Also, in order to have estimate of the performance of the turbine in the scaled-up level, a similarity analysis is made. Then the results are modified to find the estimate for the performance of the array of turbines. The comparison between the estimated power of the torsional galloping turbine and some conventional turbine types gives a general idea about how this turbine would operate in full scale.

van der Pol-Duffing Modeling for Torsional Galloping

This study is a continuation of the study presented in OMAE 2012 entitled: “Stability Analysis of a Yawing Flat Plate into the Water Current”[1]. The structure in the aforementioned study consists of a rectangular flat plate with an elastic axis in its mid-chord length. The elasticity is provided by torsion spring. The flat plate has only one degree of freedom which is angular oscillation about its axis. It is observed that as the current speed exceeds a critical velocity, the flat plate becomes unstable. The instability leads to torsional galloping occurrence, as a result of which the flat plate begins to oscillate angularly about the elastic axis. Through the present study, a phenomenological model is developed based on van der Pol-Duffing equation, in order to explain the instability leading to the torsional galloping.