Publication: Aeroelastic calculations on an equivalent beam-based NASA CRM
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2019-09-23
Defense date
2019-10-18
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Abstract
Aircraft design is a very complex discipline strongly characterized by mutlidisciplinarity. Each discipline needs to be properly modeled for reliable results favoring a smooth transition from the early design stages up to the certification in compliance with airworthiness regulations. When considering structures, a detailed description of the wing requires very large finite element (FE) models. Such level of detail is indeed needed when local behaviour is studied. However,aeroelasticphenomenalikefluttertypicallydependonlargerscalefeatures. For this reason simpler model retaining the relevant physics are usually employed. Insuch effort, a flutter-equivalentbeam-based model ofthe wingbox ofthe NASACommon Research Model (CRM) is developed. In order to achieve the equivalence of this complex model, first three simpler study models and their equivalent beam-based models are created, following a progression in complexity; being the first one a straight box, the second one a straight wing box with the typical wing components (skin, spars and stiffeners) and the last one a swept wing box. The equivalence of the models both statically and dynamically (modal analysis) is checked. Then, it is time to start working with the NASA Common Research Model. First, a MATLAB code is developed in order to be able to calculate the different cross-sectional propertiesalongthespanofthewing. Then,theribsandthenon-structuralmasses(flaps) are added to the beam-based model. Once the equivalent beam is fully created, the static and dynamic equivalence are checked, observing that while low order modes are well replicated in the beam, the error increases with higher order modes, where local effects of the CRM are not seen in the beam. Finally, the flutter analysis is conducted on both models, observing that the evolution ofthedampingandfrequencyissimilaruntilvelocitiesof250m/sarereached,wherethe shape of the modes is of great importance and more error is obtained, therefore not being able to predict flutter in the simpler beam-based model.
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Flutter, Beam-based mode, Equivalence