F-15 Velocity Spectra

The velocity fluctuations slightly upstream of a 1/32-scale F-15 vertical tail tip chord is measured using hot-film anemometry.  The velocity data is then Fourier transformed into the frequency domain and the spectra is obtained.  Figure 1 shows the velocity spectra at a fixed angle of attack at various freestream velocities.  The characteristic spectral feature present in this flowfield is a narrow band peak, indicating a nearly periodic fluctuation at the F-15 tails.  With increase in freestream velocity the frequency corresponding to the spectral peak also increases.  We investigated how this peak frequency varies with velocity.  Frequency vs. Velocity

 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