High-speed Civil Transport Wing Research Articles

Analysis Tools for the Detection of IntermittentNonlinear Aeroelastic Phenomena

The nonlinear coupling between the aerodynamic load and structural motions in the experiments conducted in the Langley Transonic Dynamics Tunnel at NASA Langley Research Center on a flexible semispan model (FSM) of a high-speed civil transport wing configuration is examined. The results show that, right before hard flutter took place, the aerodynamic load and the structural motion of the FSM were intermittently and quadratically coupled. Particularly, the shock motion, which can be caused by local and intermittent flow separation, is nonlinearly related to the structural motion in such a manner that one full cycle of the shock motion is related to two cycles of the acceleration of the wing tip. Because of the required averaging in implementing them, Fourier-based higher-order spectral moments could not characterize this coupling. On the other hand, the wavelet-based cross bicoherence is established as a tool that is capable of detecting intermittent or transient nonlinear aeroelastic phenomena as would be encountered in model studies or flight tests.

Flutter of High-Speed Civil Transport Flexible Semispan Model: Time Frequency Analysis

Time/frequency analysis of fluctuations measured by pressure taps and strain gauges in the experimental studies of the flexible semispan model of a high-speed civil transport wing configuration is performed. The interest is in determining the coupling between the aerodynamic loads and structural motions that led to the hard flutter conditions and loss of the model. The results show that, away from the hard flutter point, the aerodynamic loads at all pressure taps near the wing tip and the structural motions contained the same frequency components. On the other hand, in the flow conditions leading to the hard flutter, the frequency content of the pressure fluctuations near the leading and trailing edges varied significantly. This led to contribution to the structural motions over two frequency ranges. The ratio of these ranges was near 2:1, which suggests the possibility of nonlinear structural coupling.

Prediction of Crack Growth Under Variable-Amplitude and Spectrum Loading in a Titanium Alloy

Abstract The present paper is concerned with the application of a plasticity-induced crack-closure model, FASTRAN, to predict fatigue-crack growth under various load histories in a thin-sheet Ti-62222 STA titanium alloy. This alloy was a leading candidate for a metallic High-Speed-Civil-Transport (HSCT) aircraft in the United States. The crack-growth model was based on the Dugdale strip-yield model but modified to leave plastically deformed material in the wake of the advancing crack. The model includes the influence of “constraint” on the development of plasticity and closure during constant- and variable-amplitude load histories. The model was used to correlate crack-growth-rate data under constant-amplitude loading over a wide range in crack-growth rates and stress ratios at two service temperatures (room temperature and 175°C). Tests on repeated spike overloads were used to help establish the constraint variations in the model. The model was then used to predict crack growth under two simulated aircraft spectrum load histories at the two temperatures. The spectra were a commercial HSCT wing spectrum and the Mini-TWIST (transport wing spectrum). This paper will demonstrate how constraint plays a leading role in the retardation and acceleration effects that occur under variable-amplitude and spectrum loading. The model was able to calculate the effects of repeated spike overloads on crack growth at the two temperatures, generally within about ± 30%. Also, the predicted crack-growth behavior under the HSCT spectrum agreed well with test data (within 30%). However, the model under-predicted the fatigue-crack-growth behavior under the Mini-TWIST spectrum by about a factor-of-two. Some of the differences may be due to fretting-product-debris-induced closure or three-dimensional effects, such as free-surface closure, not included in the model. Further study is needed on life predictions under the Mini-TWIST flight spectrum.

Jig-Shape Static Aeroelastic Wing Design Problem: A Decoupled Approach

A novel approach to the jig-shape static aeroelastic wing design problem is presented in this paper. Unlike previous design efforts where the aerodynamic and structural analyses were coupled throughout the optimization process, this work presents a truly decoupled approach. The proposed approach performs aerodynamic shape optimization in the first phase to determine an optimal configuration, followed by structural shape optimization in the second phase to find the corresponding jig shape. The latter does not require the performance of any new aerodynamic analyses, resulting in true decoupling of the jig-shape aeroelastic wing design problem. This results in significant reduction in computation time making the design of relatively complex wing structures feasible. For this study high-fidelity codes-ANSYS 5.0 for the structural analyses and a supersonic Euler code for the aerodynamic analyses-were used. A modified simulated annealing algorithm was used as the optimizer. Two examples are presented a forebody problem and the design of a high-speed civil transport wing, to demonstrate the efficacy of the methodology.

Response Surface Approximations: Noise, Error Repair, and Modeling Errors

In the past few years there has been interest in using response surface techniques to create surrogates to computer simulations. Response surface techniques allow detection and correction of errors as well as filtering out numerical noise, but these techniques introduce additional modeling errors. Methods of reducing both noise and modeling errors are explored. It is also demonstrated that repairing designs with large errors is preferable to eliminating these designs from consideration. Response surface approximations for a high-speed civil transport wing weight equation created from the results of a large number of structural optimizations are used for demonstration. It is shown that the statistical tools available for response surface techniques are effective for error detection and for filtering out noise. Once the noise is reduced, modeling errors can also be reduced by increasing the order of the approximation.

Variable-complexity aerodynamic optimization of a high-speed civil transport wing

A new approach for combining conceptual and preliminary design techniques for wing optimization is presented for the high-speed civil transport (HSCT). A wing-shape parametrization procedure is developed which allows the linking of planform and airfoil design variables. Variable-complexity design strategies are used to combine conceptual and preliminary-design approaches, both to preserve interdisciplinary design influences and to reduce computational expense. In the study, conceptual-design-level algebraic equations are used to estimate aircraft weight, supersonic wave drag, friction drag, and drag due to lift. The drag due to lift and wave drag are also evaluated using more detailed, preliminary-design-level techniques. The methodology is applied to the minimization of the gross weight of an HSCT that flies at Mach 3 with a range of 6500 mi.