Aerodynamic Buffet Onset Boundary Estimation of a Jet Trainer Aircraft

Abstract

Buffeting is associated with the flow instabilities around aircraft components, especially wing, horizontal and vertical tails due to boundary layer separation. The occurrence of separated flow over the surface can cause a source of energy to induce vibrations in the airframe. These may take the form of undesirable rigid body motions that adversely affect performance or handling characteristics. Boundary layer separation can occur either due to a high angle of attack in the whole aircraft velocity spectrum or be induced by shockwave/boundary layer interactions over the wing surfaces at transonic speeds. It is crucial to specify a safe initial flight test envelope for a newly designed aircraft to test for initial airworthiness, flying qualities, and performance prior to flight tests concerning aerodynamic buffeting. Throughout this paper, the buffet onset boundary investigation of a jet trainer aircraft is performed for the transonic flow regime based on wind tunnel and numerical simulation data. Deviations of the high-frequency data obtained from wind tunnel pitch-and-pause measurements are examined to identify shock buffeting onset. Also, Unsteady Reynolds-Averaged Navier-Stokes Computational Fluid Dynamics analyses are performed for several flight conditions to observe the shock travel distances and vertical acceleration fluctuations. It has been shown that the shock buffeting phenomenon is observed in similar characteristic values for both Unsteady Reynolds-Averaged Navier-Stokes solutions and wind tunnel test data. Moreover, low speed and high angles of attack buffet onset investigation is performed based on numerical simulation data. Scale-Adaptive Simulations are performed at low speed, high angles of attack to predict buffet onset and visualize the vortices induced by strake and wing tip.