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

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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.