Frequency vs. Velocity

Selecting the frequency corresponding to the spectral peaks in Figure 1, the plot of frequency versus velocity shown in Figure 2 is made.  Shown are data at angles of attack equal to 20° and 28°.  A distinctly linear relation is seen for all the angles of attack tested.  This type of linear relationship has been shown on very swept wing configuration tested to date.  Taking a linear curve fit of the data at a given angle of attack, the relationship between peak frequency and velocity can be expressed as the slope.  The slope then varies also as a function of angle of attack.  To characterize the spectral peak frequencies, the slopes are found for each angle of attack where spectral peaks are present.  At very high angles of attack, above 32°, the broad band spectra of  turbulence is seen.     Reduced Frequency

 F-15 Tail Buffet Alleviation Results
F-15 Velocity Spectra    Frequency vs. Velocity    Reduced Frequency
4.7% F-15 Torsion    4.7% F-15 Bending    Empirical Prediction vs. Test Data