Buffeting Problems Modelling by Use of Lifting Surface Methods in Unsteady Aerodynamics with Separation

Abstract

The analytical approach to buffeting problem in subsonic flow is a challenging one and has been given attention by many researchers; no purely analytical approach has been satisfactorily capable of simulating the phenomenon. An attempt to develop a computational method for the calculation of the aerodynamic load for separated subsonic flow using kernel function technique in linearized aerodynamics has been made by the author and his associates, as an alternative to the more accurate but elaborate technique of direct numerical attack to the viscous flow problem. Two approaches were then made. First, to treat the buffeting problem as a stability one by solving the flutter equation. Second, treating buffeting problem using dynamic response approach. Comparison of the unsteady load calculation method with other existing results for non-separated flow cases indicated good agreements. For separated flow case, no other methods are available for comparison. However, flutter solution approach made by the present study indicated that the presence of the separation bubble tends to destabilize the system compared to the attached flow case. The analytical approach to the buffeting problem using dynamic response technique was made by assuming that there is no coupling between the motion induced unsteady loads and the independent-motion unsteady loads. The motion induced unsteady airloads is calculated using the present method while the buffeting excitation load was based on experimental data. Computational results for the bending moment of a wing experiencing buffeting with experimental results indicated good agreement but lower values for the onset of buffeting.