Velocity fluctuations a small distance upstream of the vertical tails were measured through hot-film anemometry. Narrow-band spectral peaks are present in the flowfields of each model tested. This phenomon exhibits a distinctly linear relationship between the frequency corresponding to maximum peak amplitude and freestream velocity. Due to this linear relationship, a reduced frequency, n, can be defined as the slope of the frequency/velocity multiplied by the model span ( n=(df/dV)*s ). For a given angle of attack, this gives a single emperical parameter for the peak flow excitation frequency once given model size and flight speed. Scaling to full scale appears successful based on F-15 tail buffet data.
F-15 Tail Buffet Alleviation Results
Reduced Frequency Scaling: Linear Peak Frequency/Velocity Slopes: Models Tested:
Empirical Peak Frequency Data: Surface Fence Tests: Reduction in Spectral Intensity:
Reductions Over all Angles: Comparison with Flight Tests: Summary:
Future F-15 Wind Tunnel Tests: