Efficiency enhancement of pulsed-jet actuators through duty-cycle optimization

将流体脉动地注入到横流边界层中是防止或延迟其从固体表面分离的普遍方法。尽管在机翼模型上研究了几十年，但这种方法简化机械复杂的增升构型的潜力在飞机工业中尚未使用。从空气动力学的角度来看，这主要是由于产生脉冲射流的设备的过度质量流消耗。在这个项目中的首要目标是建立一个新的方法来选择分离控制参数，导致一个显着减少的质量流量消耗，同时保留控制权。在第一个资助期（2019-2022年），脉冲射流的基本特性得到了解决，从而揭示了特征涡结构和与所研究方法的功能原理相关的潜在机制。作为一个主要的发现，一个流动固有的时间尺度管理的复发后，通过脉冲射流的动量添加流分离已被确定在一个通用的设置。由于可以优化连续脉冲之间的时间延迟，因此可以显着节省质量流量。实验结果也证实了我们最初的假设，因为减少驱动占空比确实会导致系统的效率增益。在第二个资助期内，这些结果将转移到一个更相关的空气动力学社区的流动配置，同时解决在这种应用中出现的实际问题。具体地说，一个带有简单铰接襟翼的有限翼展机翼模型将配备一组脉冲射流作动器，以对抗襟翼上的边界层分离。首先，我们将评估在第一个资助期内建立的方法是否可以应用于这种与应用相关的设置。然后，将考虑由于周期致动而发生的动态载荷，并将相移强迫信号作为潜在的对策进行评估。最后，相邻的致动器出口之间的间距将进行调查，代表了进一步的手段，以减少质量流量consumption.The调查结果，预计在这个项目中获得的允许在未来的分离控制应用程序的操作参数的更明智的选择。

The pulsatile injection of fluid into a cross-flowing boundary layer is a widespread method to prevent or delay its separation from a solid surface. Despite being investigated on wing models for decades, the potential of this approach to simplify mechanically complex high-lift configurations is yet unused in the aircraft industry. From an aerodynamics perspective, this is mainly due to the excessive mass-flow consumption of the devices generating pulsed jets. The overriding objective in this project is to establish a novel approach for choosing separation-control parameters that lead to a significant reduction of the mass flow consumption while retaining the control authority. During the first funding period (2019-2022), fundamental properties of pulsed jets have been addressed, shedding some light on characteristic vortical structures und the underlying mechanisms associated with the function principle of the studied method. As a major finding, a flow-inherent time scale governing the recurrence of flow separation subsequent to the momentum addition by means of pulsed jets has been identified in a generic setup. This gave rise to significant mass flow savings as the time delay separating successive pulses could be optimized. The experimental findings have also corroborated our initial hypothesis inasmuch as a reduction the actuation duty cycle indeed leads to systematic efficiency gains.During the second funding period, these results will be transferred to a flow configuration that is more relevant to the aerodynamics community while addressing practical issues that arise in such applications. Specifically, a finite-span wing model with a simple-hinged flap will be equipped with an array of pulsed-jet actuators to counter boundary layer separation on the flap. First, we will estimate whether the method established during the first funding period can be applied to this more application-relevant setup. Then, the occurrence of dynamic loads due to the period actuation will be considered and phase-shifted forcing signals will be assessed as a potential counter-measure. Finally, the spacing between neighbouring actuator outlets will be investigated, representing a further means to reduce the mass flow consumption.The findings obtained in this project are expected to allow for a more informed choice of operating parameters in future separation control applications.