  The problem of reducing noise in the transportation is an important research
field to prevent accidents and to provide a civilized environment for people. A
material that has recently attracted attention in research to reduce noise is
acoustic metamaterial, and most of the research projects so far have been
limited to the case of static media without flow. We have studied the sound
transmission properties of acoustic metamaterial with turbulent flow to develop
acoustic metamaterial that be used in transportation. In this paper, the effect
of geometrical structure, the convective effect, and the eddy effect on sound
propagation in acoustic metamaterial with turbulent flow are investigated, and
the relationships between them are analyzed. The convective effect and the eddy
effect both reduce the resonant strength of sound transmission loss resulting
from the unique geometry of the acoustic crystal, but shift the resonant
frequencies in opposite directions. In addition, when the convective effect and
the eddy effect of the airflow, as well as the intrinsic interaction effect
generated from the unique geometrical structure of the acoustic metamaterial
cannot be ignored, they exhibit competition phenomena with each other,
resulting in a widening of the resonance peak. As a result, these three effects
cause the shift of the resonance frequency of the sound transmission loss and
the widening of the resonance peak. The results of this study show that even in
the case of turbulent flow, acoustic metamaterial can be used for
transportation by properly controlling the geometric size and shape of the
acoustic metamaterial.
