Introduction

The motivation for this work developed from the tail buffeting problems experienced by a number of today's twin-tailed fighter aircraft. The two most notable cases are the F/A-18 and F-15.  There is currently a vast data set available on the subject of vortex burst and its fatigue effects on tail surfaces.  On the F/A-18 at angle of attack, the flow field is dominated by strong vortices generated over the wing leading edge extensions (LEX).  These strong vortices undergo a rapid expansion and violent break down at certain flight conditions such that the tails are engulfed in intense broad-band turbulent velocity fluctuations.  The tails are driven to buffet by this intense fluctuating flow energy.  On the contrary, the F-15 flow field does not have a strong leading edge vortex present, and the vortex motion present is referred to as wake-like (with axial velocities in vortex center a fraction of the freestream).  In this flow field where the vortex burst phenomenon is not the dominant feature, nearly periodic velocity fluctuations are present at the top of the vertical tails.  This much lower intensity flow excitation, due to its frequency variation with angle of attack and velocity, is presumed to at some flight conditions "tune" to the tail structural modes.  This is seen to be the driver of tail buffet on the F-15.  Methods of predicting these flow fluctuation frequencies  and methods of attenuating their energy are presented in this work.
 

 
 
 
 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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