Cross-Sectional Sizing of Rotor Blades with Dynamics and Strength Constraints

The reduction of vibratory loads on a helicopter rotor hub can be achieved by intricately designing the inner structure of the rotor blades. However, the vast design space, the nonlinear complexity of the problem and prolonged computational times pose significant challenges. This paper introduces an automated design optimization process utilizing surrogate models, employing both commercially available software and codes developed within DLR. Among the codes put to use is VAST - the new rotary wing aircraft comprehensive aeromechanics analysis being developed at DLR. The primary aim of the process is to minimize human intervention and enhance the overall process efficiency. The framework incorporates the Latin Hypercube Sampling function for designing experiments, the Kriging function for surrogate modeling, and the particle swarm optimization algorithm. Design variables encompass the parameters of the rotor blade inner structure including composite skin layup angles while vibration index serves as the objective function. The use of lumped masses as a passive vibration reduction technique is an innovative feature here. Both the radial as well as the chordwise location of the lumped masses have been taken as additional design variables. The outcomes demonstrate that meticulous inner structure design can yield a rotor with diminished hub vibratory loads.