Performance Optimization of Variable-Speed and Variable-Geometry Rotor Concept

This paper discusses the application of a particle swarm optimization technique to a rotor dynamics analysis to perform multivariable optimization for minimizing power output for a variable-speed variable-geometry rotor system. A UH-60A Black Hawk helicopter rotor operating at a weight coefficient of C-w = 0.0065 is taken as the baseline configuration to study the impact of power reduction through speed and geometry optimization. With the objective of keeping the computational cost low, a rotor dynamics model with the assumption of rigid blades having only flap degree of freedom is developed and coupled to a nonlinear aerodynamic model that has airfoil lookup tables, attached unsteady aerodynamic model and Drees inflow model. The rotor dynamics model is then validated using the flight-test data available in literature. The main rotor power is taken as the fitness function for the particle swarm optimization, and single-variable and multivariable optimizations are carried out to systematically establish the relative significance of various optimization parameters for power minimization. Blade parameters such as radius, chord, trailing-edge plate extension, rotor speed, and blade twist are optimized. For the forward-flight conditions analyzed, the multivariable optimization using all parameters results in a significantly higher power reduction (5.4 to 12.2% more) than that attainable through the optimization by single variables. The rotor speed, radius, and chord (in that order) are the most significant contributors to total power reduction in the multivariable optimization, followed by twist and trailing-edge plate extension.