High-fidelity Aerostructural Optimization of a High Aspect Ratio Tow-steered Wing

Abstract

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 is surprising that most aircraft today are only scratching the surface of the true potential of composite technology with traditional uniaxial fibers. With the introduction of Automated Fiber Placement machines (AFP), the tow 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 wings moving toward higher aspect ratios, which inevitably leads to larger deflections, it is reasonable to assume that a tow-steered composite 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 optimum result. To address this issue, we develop a framework for the simultaneous design of aerodynamic shape, structural sizing, and tow steering angles, while considering the wing flexibility. The aerodynamics are modeled using RANS CFD, while the structure is analyzed using a detailed finite-element model. Using this framework we perform two fuel burn optimization problems are performed for a high aspect ratio (AR = 13.5) baseline wing: one using a tow-steered structure and another with no steering, unsteered. The optimization was performed with respect to tow-steering design variables, wing airfoil shapes and twist, as well as structural thicknesses. Along with including design variables which controlled the tow-steering parameterization, geometric shape variables were also included to vary the shape of the wing. The tow-steered wing was able to decrease the wing mass by 13% relative to the baseline unsteered wing.

Aeroelastic Tailoring of a Representative Wing Box Using Tow-Steered Composites

“…This effect stiffens the leading edge and allows the thickness there to reduce, whilst maintaining the same load alleviation in the rear-spar break area as for the VAT configuration. Similar laminate rotation angle distributions and mass reductions factors were recently found by Brooks et al [22] for a higher aspect-ratio wing derived from the NASA CRM model, although that study included additional structural and wing shape variables that are not considered here.…”

“…Up until the present time, mainly one-dimensional (spanwise) tow-steering have been considered. Although Brooks et al [22] presented results for a two-dimensional fiber angle variation in the skins, no comparisons were made with spanwise (one-dimensional) optimizations, leaving the potential benefits unclear.…”

“…Tow-steering was shown to reduce the wing mass compared to straight fiber configurations by up to 6% under maneuver load and flutter constraints. Brooks et al [22] also recently used a coupled Finite Element Method (FEM)/ Computational…”

An Efficient Parallel Overset Method for Aerodynamic Shape Optimization

“…This framework was developed to perform aerostructural design optimization studies of aircraft configurations [8,9], and integrates modules for CFD, structural analysis, geometry parametrization, and numerical optimization. MACH has been used extensively for both aerodynamic shape [10,11,12,13,14] and aerostructural design optimization [15,16,17,18] of aircraft and also hydrofoils [19]. Here we use only the aerodynamic capabilities Figure 19: Strong scaling speedup for the IHC overset connectivity algorithm.…”

Design and Testing of Aeroelastically Tailored Wings Under Maneuver Loading

“…[4][5][6][7] More specifically, research has been done on the use of aeroelastic tailoring in order to minimize structural weight, [8][9][10][11] maximize flutter speed, 10,[12][13][14][15] optimize the gust response characteristics of the wings, 16 or the effect of tow-steered composites on wing aeroelastic characteristics. 17,18 Several researchers [19][20][21] have used a gradient-based optimiser with adjoint sensitivities to achieve aeroelastic tailoring by optimising a combination of laminate thickness and the fraction of 0 deg, 45 deg, −45 deg, and 90 deg plies in the stacking…”