یک سیستم پیزو فعال حلقه بسته MEMS برای تاخیر فعال انتقال A Piezo-Actuated Closed Loop Mems System For Active Delay Of Transition

The active delay of transition has been a major topic in aerospace research throughout the last decades. Boundary layer instabilities (TS waves) in 2D airfoil boundary layers can cause a transition from laminar to turbulent flow, which increases the drag significantly. By launching an opposed surface wave into the boundary layer, the amplitude of the TS waves can locally be reduced and hence, the transition from laminar to turbulent flow can be delayed [1]. Current research uses loudspeakers which displace a flexible membrane to create a counter wave in the boundary layer [2,3]. These experiments have been successful but the approach using loudspeakers is limited regarding its miniaturization potential. For creating a traveling surface wave, an array of downstream cascaded actuators is desired. Loudspeakers cannot be cascaded as densely as required, what creates the need for a new, miniaturized actuator concept. Active delay of transition demands a combined sensoractuator system to detect the TS wave pattern and to cancel them by a suitable wave-like movement of the wing surface. The principal setup is shown in Figure 1. The amplitude of the TS-waves is increasing while traveling downstream across the airfoil. An array of hot wire sensors detects the incoming TS waves. Downstream of the first sensor array (reference sensor) an actuator system is placed. This system locally displaces an elastic cover. In order to induce a real traveling surface wave into the boundary layer, several actuators that are cascaded within one TS wavelength (in the performed experiments typically in the range of a few cm) are needed. Downstream of the actuator system, at least one further sensor (error sensor) is necessary. This sensor measures the success of reducing the disturbance amplitudes and feeds back the information to the control. A schematic of the control principle is shown in Figure 2. The control uses a filter based approach (finite impulse response, FIR [4]) to calculate an actuator signal that minimizes the signal amplitude of the error sensor. As the TS-waves occur randomly, the calculated transfer function of the control for driving the actuator has to be continuously adapted. As a first step within this project, an actuator prototype has been developed that consists of only one piezo-polymercomposite (PPC) actuator. The goal is to prove the principal suitability of the PPC technology for active delay of transition. This paper presents the development of this prototype and its evaluation in first wind tunnel experiments. Based on the gained experiences and insights, a system with cascaded actuators, like outlined in Figure 1, will be developed in a next step.