Low-frequency acoustic center body
A center plug includes an inner skin, the inner skin extending along an axial centerline; an outer skin positioned radially outside the inner skin; a forward bulkhead connected to and extending radially outward from the inner skin; an aft bulkhead connected to and extending radially outward from the inner skin; and an acoustic panel, the acoustic panel including a first sheet having a first plurality of perforated walls and a first plurality of non-perforated walls, a second sheet having a second plurality of perforated walls and a second plurality of non-perforated walls, the first sheet being sandwiched together with the second sheet to form an N-shaped structure having a combined plurality of perforated walls and a combined plurality of non-perforated walls.
1. A center plug for attenuating noise in a gas turbine engine, comprising:
an inner skin, the inner skin having a substantially cylindrical shape and extending along an axial centerline;
an outer skin positioned radially outside the inner skin;
a forward bulkhead disposed proximate a forward end of the inner skin, the forward bulkhead connected to and extending radially outward from the inner skin;
an aft bulkhead disposed proximate an aft end of the inner skin, the aft bulkhead connected to and extending radially outward from the inner skin; and
an acoustic panel disposed within a volume defined by the inner skin, the outer skin and the forward bulkhead and the aft bulkhead, the acoustic panel including:
a resonator cavity comprised of a plurality of sub-cavities extending axially along the axial centerline and circumferentially about the axial centerline, the plurality of sub-cavities including a first sub-cavity, a second sub-cavity, and a third sub-cavity, the first sub-cavity being separated from the second sub-cavity in a circumferential direction by a first perforated wall, the second sub-cavity being separated from the third sub-cavity in the circumferential direction by a second perforated wall,
a first perforated surface extending in an axial direction and through the outer skin and into the first sub-cavity,
a non-perforated surface extending in the axial direction and covering the second sub-cavity, and
a second perforated surface extending in the axial direction and through the outer skin and into the third sub-cavity,
wherein the second perforated surface is spaced in the circumferential direction from the first perforated surface by the non-perforated surface.
2. The center plug of claim 1 , wherein the plurality of sub-cavities is defined by a first plurality of perforated walls oriented within a first range from about minus ten degrees to about plus ten degrees with respect to a radial direction extending perpendicular to the axial centerline.
3. The center plug of claim 2 , wherein the plurality of sub-cavities is defined by a second plurality of perforated walls oriented at an angle within a second range from about forty degrees to about eighty degrees with respect to the axial centerline.
4. The center plug of claim 3 , wherein the axial direction is selected such that attenuated acoustic waves exiting the second perforated surface are out of phase with non-attenuated acoustic waves transiting downstream of the first perforated surface.