The application of robust design strategies on managing the uncertainty and variability issues of the blade mistuning vibration problem

The blade mistuning vibration problem refers to the often-dramatic scatter - and thus increase - in vibration response levels when the nominally-identical blades on a bladed disc are slightly different to each other. For example, when a set of blades have eigenfrequencies varying randomly with a 0.5% scatter about the design value, the vibration response of the individual blades can vary dramatically, with individual blades displaying increases of as much as 100-500% as compared with the level which would be observed on every blade in a perfect (i.e. “tuned”) bladed disc. As both the vibration response levels and variations of blades are physical in nature, the variation is called aleatory uncertainty or simply variability. Although the problem became a research topic over 40 years ago with more than 400 papers already published, industry still faces shortened fatigue lives due to these extreme vibration responses, with high levels of scatter and uncertainty as to the likely incidence of extreme response levels. In the paper, the blade mistuning problem is viewed as a robust design problem, where the maximum blade response on the bladed disc is the robustness. The dependence of robustness on selected design parameters is discussed, and a procedure for managing the consequences of blade mistuning on manufactured bladed discs, rather than trying to eliminate the problem, is presented.