Linear Spectral Peak Frequency/Velocity

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

Introduction:   Spectral Amplification:   Centrifugal Instabilities:
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:
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