Fin buffet pressure evaluation based on measured flowfield velocities

A method to predict fin buffet aerodynamic loads is developed based on measured fluctuating velocity fields only. This has been investigated for a model of a high-performance, single-finned, delta-canard configuration. The time-dependent velocity field is measured in the fin region, resulting in a detailed description of the properties of the buffet-inducing quantities. A modified lifting surface method is used to evaluate the unsteady fin surface pressures. It is based on the amplitude spectra of local fin incidence calculated from the measured velocities. Consequently, rms and spectral densities of fluctuating surface pressure and normal force are obtained. It is shown that the fin buffet pressures increase significantly with increasing incidence. At high incidences the buffet load spectra exhibit strong narrow-band peaks. They correspond to the quasiperiodic fluctuations present in the breakdown flow of wing and canard leading-edge vortices approaching the midsection. The results that were obtained agree very well with direct-measured fin buffet pressure. This gives strong evidence that fin buffet loads can be determined with adequate accuracy by the approach suggested in this paper.