The numerically most elaborate and demanding applications of flow-structure coupling have thus far been implemented in the area of gust simulations. In the projects iGREEN and ALLEGRA, gust experiments have been conducted in the transonic wind tunnel in Göttingen (TWG). For this purpose a 2D profile (NACA 0012), functioning as a gust generator, is set to vibrate. The gust generator produces unsteady disturbances in the flow, which in turn make the elastic wing model behind it (aero-stable wing) vibrate. In preparation for the wind tunnel tests, simulations were conducted in advance with the help of the PyCSM software to estimate the dynamic reactions and loads on the elastic wings. For the first time, a complex elastic FE model with a laminate structure as well as a complete CFD model of the TWG, including the inlet nozzle and adapted wind tunnel walls, were used, to be able to model near-real conditions in the simulation.
The model structure (CFD computational grid) of the numerical simulation of the gust experiment is shown in the above figure. Through modelling of the wind tunnel, including its inlet nozzle and adapted walls, a substantial improvement could be achieved in the numerical results.
Furthermore, extensive gust simulations using pulse excitation are conducted; the objective is to determine the transfer function of gust excitation on the dynamic response of the elastic wing to a pulse-type excitation (e.g. a strong 1-cos gust). Through such a transfer function and with the help of a time simulation, it is possible to calculate accurate gust loads with CFD that can improve the results from standard procedures in the critical speed area (transonic). Some preliminary results are shown in the figure below. The maximum bending load on the wing root of the elastic wing is shown for different gust lengths, determined using a transfer function for an excitation of a 1-cos gust (solid line). The blue dots are the results from the complete time simulations with appropriate gust frequencies and amplitudes. The results show a very good compliance.