There are a wide range of applications in which it is desirable to mitigate unsteady load fluctuations while preserving mean loading. This is often achieved with active control systems, but passive systems are sometimes more desirable for enhancing reliability. This is the case, for example, for wind and tidal turbines, where unsteady loading limits the fatigue life of the turbine and results in power peaks at the generator. Here, we consider the unsteady load mitigation that can be achieved through a foil with a trailing-edge flap that is connected to the foil via a torsional spring. We develop a theoretical model and show that the preload can be tuned to preserve the mean foil loading. The spring moment that maximises the unsteady load mitigation is approximately constant, and the load fluctuation reduction is linearly proportional to the ratio of the flap to the full chord of the foil. We verify this relationship through water tunnel tests of a foil with a hinge at 25% of the chord from the trailing edge. As theoretically predicted, we measure unsteady load mitigation of up to 25%, without any variation in the mean load. In highly unsteady flow conditions, when boundary layer separation occurs, the unsteady load reduction decreases. Overall we conclude that passive trailing-edge flaps are effective in alleviating unsteady load fluctuations and their effectiveness depends on their size relative to the foil.

有许多应用需要在保持平均负载的同时减轻不稳定的负载波动。这通常是通过主动控制系统实现的，但被动系统有时更适合提高可靠性。例如，风力涡轮机和潮汐涡轮机就是这种情况，其中不稳定的负载限制了涡轮机的疲劳寿命并导致发电机出现功率峰值。在这里，我们考虑了可以通过带有后缘襟翼的水翼实现的不稳定负载缓解，该后缘襟翼通过扭转弹簧连接到水翼。我们开发了一个理论模型并表明可以调整预载荷以保持平均箔载荷。使不稳定载荷缓解最大化的弹簧力矩近似恒定，并且负载波动的减少与襟翼与箔的全弦的比率成线性比例。我们通过在距后缘 25% 的弦长处具有铰链的箔片的水洞测试来验证这种关系。正如理论上预测的那样，我们测量了高达 25% 的不稳定负载缓解，而平均负载没有任何变化。在高度非定常流动条件下，当边界层分离时，非定常载荷减少量减少。总的来说，我们得出结论，被动后缘襟翼在减轻不稳定载荷波动方面是有效的，它们的有效性取决于它们相对于翼片的尺寸。我们测量了高达 25% 的不稳定负载缓解，而平均负载没有任何变化。在高度非定常流动条件下，当边界层分离时，非定常载荷减少量减少。总的来说，我们得出结论，被动后缘襟翼在减轻不稳定载荷波动方面是有效的，它们的有效性取决于它们相对于翼片的尺寸。我们测量了高达 25% 的不稳定负载缓解，而平均负载没有任何变化。在高度非定常流动条件下，当边界层分离时，非定常载荷减少量减少。总的来说，我们得出结论，被动后缘襟翼在减轻不稳定载荷波动方面是有效的，它们的有效性取决于它们相对于翼片的尺寸。