empirical reduced peak frequency ( n=(df/dV)*s ) is defined for each model
over the range of angles of attack which spectral peaks were present.
Data for three aircraft models and four delta wing models are given.
Moderately swept configurations (<60°) show a decrease in reduced
frequency with increase in angle of attack. The unique faceted features
of the F-117, as well as the high wing sweep, lead to the varied results
seen in the figure. It is interesting to note that spectral peaks
exist even when vortex burst location (on 59.3° delta wing) moves from
the trailing edge toward the apex. On the moderately swept wings,
no "unburst" strong vortices are present in the flow field, and yet spectral
peaks dominate the flow field. With this empirical data set, the
spectral peak frequency can be predicted on larger scale models at higher
velocities. Scaling to full scale appears successful based on F-15
tail buffet data.