The SAFE diagram is a design tool that is often used for analyzing modes of concern in bladed disks. The diagram implements the concept of phase cancellation in order to show what bladed disk modes can and cannot be excited by upstream flow obstructions. In many cases, phase cancellation theory dictates that even if a modal frequency corresponds with an excitation order, the mode may not be excited if the total work calculated by integrating the excitation profile around the mode shape is equal to zero. This paper reviews the theory behind the SAFE diagram and explores the effects of blade mistuning on SAFE diagram analysis from both theoretical and experiential viewpoints. Modal test data, mistuned finite element analysis, and two case studies all indicate that mistuned modes may not exhibit the pure nodal diameter patterns that are predicted by a symmetric analysis and are required for phase cancellation. These mistuned asymmetric modes may result in high blade stresses and blade failure even if a SAFE diagram analysis indicates that the mode will not be excited.
- International Gas Turbine Institute
Revisiting the SAFE Diagram for Analysis of Mistuned Bladed Disks
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Allison, TC, Moore, JJ, Lerche, AH, & Simmons, HR. "Revisiting the SAFE Diagram for Analysis of Mistuned Bladed Disks." Proceedings of the ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. Volume 6: Oil and Gas Applications; Concentrating Solar Power Plants; Steam Turbines; Wind Energy. Copenhagen, Denmark. June 11–15, 2012. pp. 141-153. ASME. https://doi.org/10.1115/GT2012-69014
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