Unsteady effects of the seperated flow at the tail section of a helicopter fuselage

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Unsteady effects of the seperated flow at the tail section of a helicopter fuselage

Vogel, F. / Breitsamter, C. / Adams, N.A.

The flow around a helicopter fuselage was investigated experimentally. The focus of the investigations is on the flow phenomena around the lower tail section of the fuselage and in its wake. The undisturbed flow around the lower tail section of the fuselage shows a strong positive pressure gradient, which gives an indication of flow separation. Two spots of low pressure in this area on the surface showing the generation of a counter rotating vortex pair, which also can be seen in the flow field, measured behind the fuselage. The vortex pair has a higher level of turbulence in its cores, which become noticeable on the surface by pressure fluctuations, as well as in the wake are by velocity fluctuations. The influence of the model mount on the flow around the lower fuselage tail was shown. Considering the mean flow, the flow strongly affected by the lower cylindrical strut disturbs the generation of a vortex pair on the surface of the fuselage tail. This reduces the strength of the vortices upstream in the wake. The variation of angle of attack shows a change in the surface pressure distribution, which indicates a shift in the generation of the vortex pair. For negative angle of attacks the amplification of the vortex strength and the fluctuation intensity of the surface pressure are detected. For positive angles of attack a destabilization of the vortex pair can be seen.