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Hydrogen is attracting a lot of interest in different circles these days from: propulsion, to energy storage, to personal transportation. The most obvious benefit of hydrogen fuel is a total lack of carbon in the exhaust products. This is rare for a fuel that’s a fairly high energy substance to begin with. More specifically, its high energy in terms of energy per unit of weight but somewhat less so in terms of volume.

Because of its promise as a non-polluting fuel, hydrogen is currently a very popular topic among the energy and turbomachinery communities. If hydrogen is reacted with pure oxygen, the thermal energy release is significant, and water is the only by-product. This highly exothermic reaction was used to get humanity to the moon. Of course, nitrous oxides (NOx) can be released if hydrogen is burned in air. If, on the other hand, the energy from the reaction is converted to heat and electricity in a fuel cell, then only water vapor is discharged. In addition, when pressurized in a tank, hydrogen is an easily transportable fuel, and so is desirable for transportation.

This post is about one of the most useful design tools for rotordynamics of turbomachinery: The Undamped Critical Speed Map. A critical speed map can provide a great deal of insight on the potential behavior of a rotor-bearing system without requiring a lot of model detail.