Experimental investigation of vibrating compressor blades in the presence of a periodic unsteady inlet flow

该项目将有助于从物理上理解压气机叶片对低频、小幅度激励的响应。这些激励--可能导致压气机叶片的疲劳损伤--往往建模不充分，是这种现象难以预测的原因。柏林理工大学航空发动机教席配备了一个用于气动弹性研究的运行风洞。该实验装置的测量部分由一个具有11个叶片的大型压气机叶栅组成。其中九个叶片可以通过步进电机强制在俯仰方向振动和俯冲。该设施的模块化设计构思是为了集成一个产生非稳定周期性进口流动的系统。该机构安装在压气机叶栅的上游，可以实现不同的励磁模式。在没有和存在周期性非定常进口流动的情况下，将测量和比较叶片的非定常气动响应。因此，周期性进口流动对叶片气动响应的影响将被量化。该项目的评估将重点放在低频和小幅度激励上。将通过改变激励参数和评估叶片运动和进口激励之间的相位来检验线性理论描述所调查问题的适用性。计划中的调查将以最先进的技术进行。将进行热线测量，以表征周期性的入口流动。用压阻式压力传感器测量叶片表面的非定常压力分布，用应变片测量叶片表面的振动频率和振幅。

This project will contribute to the physical understanding of compressor blade response to low-frequency, small-amplitude excitations. These excitations -- which can lead to fatigue damages of compressor blades -- are often inadequately modeled, being the causes of such phenomena not easily predictable.The Chair of Aeroengines at the Technische Universität Berlin is equipped with an operating wind tunnel for aeroelastic investigations. The measurement section of the experimental facility consists of a large-scale compressor cascade with eleven blades. Nine of the blades can be forced to vibrate in pitch and plunge by means of stepper motors. The modular design of the facility is conceived to integrate a system for generating unsteady periodic inlet flows. This mechanism is meant to be installed upstream the compressor cascade and allows to realize different excitation patterns. The unsteady aerodynamic blade responses in the absence and presence of a periodically unsteady inlet flow will be measured and compared. As a result the effects of periodic inlet flows on the blade aerodynamic response will be quantified. The assessments of this project will be focused on low-frequency and small-amplitude excitations. The suitability of the linear theory to describe the investigated problem will be checked by varying the excitation parameters and by evaluating the phase between the blade motion and the inlet excitation.The planned investigations will be performed with state of the art technology. Hot wire measurements will be carried out to characterize the periodic inlet flow. The unsteady pressure distribution on the blade surface will be acquired by means of piezoresistive pressure transducers, whereas the vibration frequency and amplitude will be retrieved with strain gauges measures.