Rapid Transonic Flutter Analysis for Aircraft Conceptual Design Applications

This study presents a new approach for the rapid transonic flutter analysis of large-aspect-ratio wings via a combination of time-linearized two-dimensional unsteady indicial functions and a database of steady two-dimensional Reynolds-averaged Navier-Stokes simulations. The approach is limited to large-aspect-ratio wings that can be discretized into multiple, streamwise, independent strips; and the well-documented strip theory with sweep corrections is applicable. This formulation allows the extension of Leishman's indicial functions (Validation of Approximate Indicial Aerodynamic Functions for Two-Dimensional Subsonic Flow, Journal of Aircraft, Vol.25, No.10, 1988, pp.914-922) to three-dimensional wings but also restricts the present method to attached flows. However, when supported with two-dimensional steady Reynolds-averaged Navier-Stokes simulations, the present method predicts flutter speeds that are within 10% of that predicted by two-dimensional time-accurate Reynolds-averaged Navier-Stokes simulations. Application of the proposed method for a large-aspect-ratio wing is validated by comparing the predicted flutter boundary against wind-tunnel experiments. More importantly, the current method predicts the transonic dip phenomena observed in the experiments but not predicted by NASTRAN analysis. This is achieved at several orders-of-magnitude lower computation time than high-fidelity time-accurate computational fluid dynamics simulations. The level of accuracy obtained at such an extremely low computation time makes the present approach very suitable for applications in conceptual design studies of large-aspect-ratio transonic vehicles.