Testing and characterizing the structural properties of rotating bladed disks can be costly and slow due to the inherent complexity and danger of high speed rotating machinery. Ideally, computational simulations should be able to predict accurate system responses with reasonable precision. Much work has gone into experimental and computational research in characterizing the structural dynamics of turbomachinery. The Gas Turbine Laboratory at The Ohio State University presents a novel excitation method using pulsed air-jets to achieve arbitrary engine order excitations at a chosen rotational speed for rotating bladed disks. The pulsed air-jet excitation system can excite a desired engine order by carefully determining the ideal firing order of the air-jets, and then doing a frequency sweep of the air-jet pulsing frequency. The frequency sweep helps ensure all blades are excited; individual blade frequencies can vary due to small mistuning effects. In the presented study, pulsed air-jets were used to excite various engine orders of a bladed disk rotating at a fixed rotational speed. The rotational speed was chosen to be outside the normal excitation speed for the engine orders investigated. Blade deflection measurements were taken with a blade tip timing system optimized for the specific engine orders of interest. Computational simulations were conducted to mimic the experiments and predict the system response using modern system modeling methods. The computational work relies on reduced order models (ROMs) to allow for efficiently and timely modeling of the full system. The computational model incorporates pre-stress effects due to the rotational velocity as well as small mistuning effects. Rotational speed effects are modeled with a parametric ROM (PROM) approach, while small mistuning effects are modeled with the component mode mistuning method (CMM). The final PROM is time integrated to capture the transient effects from the swept air-jet pulsing. The results from both the experimental and computational studies are analyzed to compare the blade amplitudes, mistuned frequencies, and blade damping values calculated from the respective data sets.


An Experimental and Computational Investigation of a Pulsed Air-Jet Excitation System on a Rotating Bladed Disk

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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