An Aero/acoustic Optimization Model - A Multiobjective, multilevel Decomposition Based Optimization Technique

An aero/acoustic optimization procedure is developed to investigate the design trade-offs associated with proprotor aerodynamic performance and acoustics. A multidiscipline, multiobjective decomposition based code OPTI-KS, suitable for tiltrotor aerodynamic and acoustic optimizations is described. Details are given related to the optimization technique employed to minimize the strength of the proprotor BVI noise while maintaining its aerodynamic efficiency in hover and cruise flight regimes. The design constraints for the rotor flight performance are confied to the hover figure-of-merit, cruise efficiency, and its Ct/sigma in descent flight condition. Proprotor aero/acoustic optimization is performed through passive blade design approach. The design variables are considered to be the blade twist, sweep, chord, and the airfoil distributions. The Aero/acoustic optimization model OPTI-KS utilizes the CAMRAD model program for its aerodynamic loads computation, the Kreisselmeier Steinhauser (KS) function for the multiobjective optimization and the WOPWOP program for rotor tonal noise calculation. Complex computational algorithm associated with the OPTI-KS is explained and the potential areas of improvement in terms of its CPU efficiency, model accuracy, and nonlinear programming are highlighted. The optimum proprotor is derived from reference model JVX proprotor, since there exists extensive experimental data for its aerodynamic performance and acoustics. The aero/acoustics optimization results show that design improvements for the BVI noise reduction through passive blade modications is possible without any significant degradation to its aerodynamic performance.