Effect of a trailing-edge jet on fin buffeting

Effect of a trailing-edge jet on the interaction of a leading-edge vortex with a fin and resulting fin buffeting was investigated in water-tunnel as well as wind-tunnel experiments. Flow visualization showed that fin-induced vortex breakdown can be delayed into the wake even for the head-on collision of the leading-edge vortex with the fin. Hence it was demonstrated that the adverse pressure gradient caused by the presence of the fin could be overcome with a deflected trailing-edge jet. Delay of vortex breakdown into the wake even for relatively small values of jet velocity ratio is possible for deflected jets, whereas the effectiveness of the jet with no deflection is very limited. Buffeting response of a flexible fin in wind-tunnel experiments showed that there was considerable delay of the onset of buffeting to higher angles of attack with increasing jet momentum for β=30 and 45 deg. Depending on the fin location with respect to the leading-edge vortex, it was possible to shift the buffeting envelope as much as 12 deg in incidence of the wing. Experiments with varying wing sweep angle showed that jet blowing was as effective in attenuating fin buffeting for less slender wings. Wind-tunnel experiments also showed that the nozzle geometry is very important and causes very different buffeting envelopes for the same momentum coefficient.