Closed loop control of stall flutter of turbo machinery blades

本课题研究利用等离子体驱动技术抑制失速颤振。叶片颤振描述了涡轮机械叶片与周围气流相互作用时的不稳定动态行为。这导致振荡幅度的快速增长，最终导致叶片的破坏。在跨声速失速颤振的情况下，由于激波后压缩而发生流动分离。本文对某型航空发动机风扇跨声速失速颤振的闭环控制进行了数值模拟。风扇的气动弹性性能将通过非定常三维计算流体动力学（CFD）模拟来评估。计算将在柏林技术中心Universität航空发动机主任的计算机设备上进行。首先确定跨声速失速颤振状态下的最不稳定工作点和最不稳定振荡模式；然后对安装等离子体作动器的风机进行数值模拟计算。通过参数化研究，得出对风机气动弹性稳定性影响最大的等离子体作动器位置。后者将通过能量法加以量化。建立了系统非定常气动响应的非线性降阶模型（ROM）。它将被用来建立一个风机的气动伺服弹性分析模型。这种低阶模型将用于控制体系结构的开发，而不需要耗时的CFD模拟。然后将控制律应用到CFD求解器中，通过高保真仿真来验证其运行情况。也就是说，将进行非定常3D模拟，以最终评估基于等离子体的闭环控制在提高风扇气动弹性稳定性方面的能力。

This project studies stall flutter suppression by means of plasma actuation. Blade flutter describes the unstable dynamic behavior of turbomachinery blades interacting with the surrounding airflow. This leads to fast growing oscillation amplitudes, which at the end results in the destruction of the blading. In the case of transonic stall flutter, flow separations occur as a consequence of post shock compressions. In this work a closed loop control for transonic stall flutter on an aero engine fan will be numerically built up.The aeroelastic behaviour of the fan will be assessed by unsteady 3D computational fluid dynamic (CFD) simulations. The computations will be carried out on the computer facility of the Chair of Aero Engines at the Technische Universität Berlin. First the most unstable operating point in the regime of transonic stall flutter and the most unstable oscillation mode will be determined. Then CFD computations of the fan equipped with plasma actuators modeled numerically will be performed. A parametric study will be carried out to derive the plasma actuator position with the highest influence on the fan aeroelastic stability. This latter will be quantified by means of the energy method. A nonlinear reduced order model (ROM) for the unsteady aerodynamic response of the system will be developed. It will be used to build up an analytical aeroservoleastic model of the fan. This low order model will be used for the development of the control architecture without the need of time consuming CFD simulations. The control law will be then implemented in the CFD solver to check its operation with high fidelity simulations. Namely, unsteady 3D simulations will be performed to assess ultimately the capabilities of the closed-loop plasma-based control in increasing the fan aeroelastic stability.