Design Optimization of Flexible Aircraft Wings Using Tow-steered Composites

[摘要] In the last 30 years since their introduction into aerospace applications, composites have become increasingly used, making up as much as 50% of modern aircraft by weight. Considering this fact, it issurprising that most aircraft today are only scratching the surface of the true potential of composite technology with traditional uniaxial fibers. With the introduction of automatic fiber placing machines, the fiber direction in laminae is now allowed to be steered spatially throughout each layer. This process is known as composite tow steering and has been shown to have improved performance over its uniaxial fiber counterpart with no additional weight penalty. With modern aircraft moving toward larger and more flexible wing designs, it is reasonable to expect that a tow-steered composite wing structure can be tailored to outperform its unsteered counterpart. However, given the highly coupled nature of the aerodynamics and structural response of the problem it is not obvious nor intuitive to find the composite fiber pattern that would yield an optimal result.High-fidelity aerostructural solvers have been proven effective for accurately capturing the trade-offs between relevant design disciplines for such aircraft.Such solvers allow for the performance of tow-steered wing structures to be analyzed in great detail.By complementing these solvers with gradient-based numerical optimization, high dimensional design spaces can be explored relatively efficiently.Such methods make it possible to quantify the maximum benefits offered by tow-steered wing structures.In this thesis, a number of aerostructural optimizations are performed to compare the performance of aluminum, conventional composite and tow-steered composite wing designs.For these studies, a set of benchmark aeroelastic aircraft models are developed based on the NASA Common Research Model.A design parameterization scheme, constitutive model, and relevant manufacturing constraints are then developed for tow-steered structures.A fuel burn minimization is then performed for a tow-steered and conventional composite wing design.When applied to a Boeing-777-type aircraft wing, tow steering is found to offer improvements of up to 2.4% in fuel savings and 24% in wing weight under the limited set of design constraints, relative to the optimized conventional composite design.This improvement was found to be due to a combination of improved passive aeroelastic tailoring and local strength tailoring in high-stressed regions in the tow-steered structure.For a higher aspect ratio wing design improvements of up to 1.5% and 14% in fuel savings and wing weight are found.Finally, the trade-off between structural weight and fuel burn performance is explored through a Pareto front study.This study compares the performance of an aluminum, conventional and tow-steered composite wing.In this study, it is found that when wing planform is free to vary, tow-steering offers improvements of up to 1.5% in fuel savings for a fuel-burn-optimized design and 1.6% in total aircraft weight savings for the structural-weight-optimized.

[发布机构] University of Michigan

[效力级别] Tow-steered composites

[关键词] Multi-disciplinary design optimization;Tow-steered composites;Aeroelastic wing design;Aerospace Engineering;Engineering;Aerospace Engineering