Probabilistic Methods to Determine Resonance Risk and Damping for Rocket Turbine Blades

摘要

The liquid oxygen-hydrogen J-2X rocket engine, which powers the upper stage of the NASA Space Launch System, is presently undergoing hot-fire testing. Analysis revealed numerous potential resonance issues with hardware in the turbomachinery flowpath, which could be catastrophic for the launch vehicle. This paper describes a series of probabilistic analyses incorporating nondeterministic characteristics of mistiming amplification, blade damping, natural frequency, and speed to assess the risk of failure of turbine blades due to resonance during past and present tests and to determine an appropriate value of damping to use hi deterministic forced response analysis. The analyses are the first reported in the literature combining these critical nondeterministk parameters. The new damping determination technique developed here indicates that combining a damping value in the lower 1.5 sigma range with a 3 sigma mistuning amplification value results in a desired total 3 sigma probability of failure. These risk calculations were invaluable for determining high-cycle-fatigue margins of safety and in determining if risk-reduction methods such as dampers were necessary immediately, or if tests could be performed before risk-reduction hardware was ready.