Improved Computational Strategies for Rotor Blades Presenting High Gradients in Sectional Properties

Sharp gradients in sectional property distributions are inherent to rotor blade design and manufacturing practices. The accuracy of finite element models of such rotor blades rapidly degrades if sharp property gradients occur within a single finite element. To remedy this situation, two techniques are developed. First, rather than using equally spaced elements, a mesh optimization procedure is developed that is based on a measure of local sectional property gradients. Next, a sectional property smoothing technique is proposed that is based on conservation arguments for mass properties and energy considerations for stiffness properties. Numerical experimentation shows that the use of both mesh optimization and sectional property smoothing considerably reduces computational errors in finite element predictions in the presence of such gradients, and leads to considerably more monotonic convergence characteristics of the computational process. When the proposed techniques are used, computational requirements are decreased because specified levels of accuracy are achieved for models featuring fewer degrees of freedom; furthermore, better accuracy is obtained when evaluating internal force and moment distributions in the blade.