Wind Tunnel and Water Tunnel Studies of Vertical Fin Buffeting

Kurzfassung

Many advanced combat aircrafts operating at high angles of attack experience unsteady vortex flows with strong pressure fluctuations which cause problems such as vertical fin buffeting. This paper presents selected results of comprehensive wind tunnel and water tunnel tests. Sharply peaked spectra of the surface pressure fluctuations on each side of the fin are observed at high angles of attack. Unsing the dominant frequency in the vortical flow field a characteristic value of a reduced frequency parameter could be obtained for the considered model configurations. Employing Digital Image Velocimetry in the water tunnel the instantaneous flow field over the model was studied. A nearly periodical oscillation of the velocity vectors has been observed in front of the leading edge of the fin. The oscillation is mainly driven by the vortex shedding from the leading edge of the main wings and induces a periodic side force on the fin.