Abstract:
A conventional flag is placed downstream of inverted D cylinder to study noise over the flags
surface as a result of fluid-flexible body interaction between the flag and the vortices generated
by the D cylinder. A noise prediction algorithm is proposed which couples with the improved
immersed boundary method to predict flow noise over flags surface. The effect of flow patterns
on flag surface noise and drag coefficient is studied by varying flags distance from the bluff
body. Results show high flag surface noise at smaller stream-wise distance and low coefficient of
drag. A subsequent decrease in flow noise is observed along with an increase in drag coefficient
as the stream-wise distance is increased. Changing span-distance shows the highest noise occurs
at Gy=0.25 with a significant drop at span positions of 0 and 0.25. The noise level is also affected
by the vibration modes and the vortex shedding from the surface of the flag. The deflected mode
appears at smaller stream-wise distance accompanied with additional vortex shedding from the
flag surface resulting in high noise level. Whereas, biased and conventional flapping modes
appear as stream-wise distance is progressively increased resulting in reduced noise levels.
Analysis shows the vortices originating from the bluff body and their subsequent interaction with
the flag serves as primary source of noise level over the flags surface.
