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Completed TRL 4 (started at 1, targeting 6)
Turbine blade cracking and failure due to operation at modal resonance costs the turbine industry (rocket engine turbomachinery, power, jet engines, etc.) $100M’s per year. In addition, the recent move towards integrally bladed-disks (blisks), which reduces part count by an order of magnitude and therefore manufacturing costs, also eliminates damping at the blade/disk interface, exacerbating the problem. In March 2019 the author received funding to initiate a design, fabrication, and test program taking advantage of Additive Manufacturing capabilities to integrally fabricate a tuned-mass vibration absorber into the blade. The first single-blade prototype, in which the absorber consists of a span-wise internal column, was tested in a shaker and showed a 47% reduction in resonant response, but a labor-intensive electro-discharge-manufacturing process was required to remove support-lattice of the column. Additional funding was awarded for 2020 to fund fabrication of prototypes of improved designs. The first of these improved prototypes places the column damper in a parallel arc to the chord of the blade so that it can be fabricated without the need for a support lattice, and its elliptical cross-section has been analytically optimized to minimize resonant forced response. This design results in a 51% reduction in analytically predicted response, but verification through fabrication and testing has been delayed due to the current pandemic. A number of related concepts have been published or patented, but they all have significantly higher costs and/or require un-validated advanced nonlinear analysis techniques for prediction of the response, so this design should prove extremely valuable to the propulsion community.
The commercialization potential for this design is significant. The turbine industry is estimated to be valued at roughly $90 billion annually worldwide as turbines provide a significant portion of worldwide power generation and all of the jet engines for transportation, as well as many other industries. Turbine blades within these different applications look remarkably similar, and exhibit the same kinds of problems, and high cycle fatigue from resonant response is one of the most significant of these problems. While the exact dimensions of the design prototype design used here would not be applicable for different specific turbine blade applications, the chord-wise TMA concept and optimization schemes outlined in this NTF can be directly implemented for industry-specific dimensions. Although it can be argued that most turbine manufactures endeavor to create overall turbine designs in which the primary modes are not excited, almost all manufacturers attempt to implement some sort of scheme to reduce the response of these modes, and this has proven so difficult with blisks that it has frequently prevented their use (with the manufacturer relying instead on much more expensive inserted-bladed-disks).[i] In addition, it is almost impossible to avoid resonance with all blade modes, and the design developed here can be optimized to reduce the response of potential up to six different modes of interest (with three different parallel absorbers). Finally, it has been postulated that this same concept could be applied to other flow-path components within turbomachinery that have resonant response issues as well, including turbine stators, vanes, and pump-side inducer and impeller blades.
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