Reduced Frequency Scaling

Reduced peak frequency, in the form of Strouhal number, has been shown to scale with freestream velocity and model scale.  Strouhal number is defined as peak frequency times model length scale divided by velocity.  A nearly constant Strouhal number is seen through  three orders of magnitude of Reynolds number and multiple model scales, to full scale flight tests.  Scaled model tests appear to capture the principle physics responsible for tail buffet on this aircraft.  This also suggests that scaled model test data can be scaled up to full scale for the prediction of dominant frequencies on future fighter configurations.  Wind tunnel test data can then be used in the design process to better understand the life-cycle factors, leading to better designed tails.

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: