A Multidisciplinary Design Environment for Composite Rotor Blades

Abstract

Aeroelastic effects are significant design drivers in rotorcraft design. Typically, detailed structural information of the rotor blade necessary to determine its cross-sectional mass and stiffness properties is not available early on in the design process, especially for complex composite blades that are being employed in modern rotor systems. A 3D finite element (FE) approach does not easily lend itself to conceptual and preliminary design due to the effort required to create a 3D model and the associated run times for solving the FE problem. Classical 1D beam analysis of the rotor blade is fast and easy to use early in the design process, but does not take into account realistic cross-sectional properties of the blade, resulting in only low-fidelity aeroelastic models. Therefore, high-fidelity aeroelastic analysis is usually not done until late in the rotorcraft design process, when changes to the design are difficult and costly to implement. The present work addresses this need for a design environment that combines the computational efficiency and speed of 1D beam analysis with high-fidelity accuracy approaching that of a 3D FE model. The environment contains a graphical modeling tool to rapidly define the cross sectional layup of a rotor blade or wing and a cross section mesh generator, both part of the IXGEN pre-processing tool. It uses a cross sectional beam analysis code (UM/VABS) to determine the cross sectional mass and stiffness properties, which it then feeds into a comprehensive rotorcraft analysis code (RCAS). Providing the option to use either DAKOTA or Phoenix ModelCenter as the optimization software, a full multidisciplinary design and optimization environment for the preliminary design of composite rotor blades and wings has been developed. As a test case, structural optimization case studies are presented where the cross-sectional layup of the blade is determined which results in significant vibration reduction at the rotor hub in forward flight conditions for the NASA/Army/MIT Active Twist Rotor (ATR) blade.