Abstract:
One of the primary research themes for NASA's Revolutionary Vertical Lift Technology Project (RVLT) is evaluation of low-noise vertical lift concepts and configurations. A multidisciplinary design analysis and optimization (MDAO) process, which incorporates acoustics, structures, icing, and impact dynamics design constraints, is in development for the conceptual low-noise rotor blade design. Modifications to conventional rotor blade shape, cross section, and material selection to reduce noise may be limited by the capability of the structure to withstand a bird strike. The bird strike requirement for transport category rotorcraft is specified in 14 CFR §29.631, and requires safe flight and landing following impact of a 2.2 lb bird. An artificial bird simulant has been developed for repeatable laboratory testing, and consists of ballistic gelatin infused with phenolic microspheres. Ballistic testing of a bird simulant on various flat and wedge shaped objects was conducted at NASA Glenn Research Center's Gas Gun Facility. Force and strain data were compared to impact simulations of an LS-DYNA® finite element model (FEM). The bird simulant was modeled using Smooth Particle Hydrodynamics (SPH), and validated based on the data. The bird simulant model was incorporated with a low noise blade design that was verified for aeroelastic stability and contained dimensions typical of a medium lift category rotorcraft. FEM pre-processing capabilities were utilized to morph the cross section to different dimensions, and LS-DYNA analyses were conducted. A parametric assessment of damage will be discussed, with varying factors such as spar thickness, blade thickness, and nonlinear material strength parameters. The geometric constraints on this low noise blade that will be used for follow-on MDAO analyses are a combination of maximum blade twist of 15 degrees and a minimum spar thickness of 50% of the nominal spar thickness.