Composite skins having variable hole sizes and shapes formed using photomachining
A face skin for an acoustic panel may comprise a sheet defining a first surface and a second surface. A plurality of slots may be formed through the face skin using abrasive blasting. Each slot of the plurality of slots may comprise a first semi-circular wall and a second semi-circular wall opposite the first semi-circular wall.
1 . A face skin for an acoustic panel of a gas turbine engine, the face skin comprising:
a sheet having a first surface and a second surface opposite the first surface; and
a plurality of slots extending from the first surface to the second surface, wherein each slot of the plurality of slots is defined by, at least, a first semi-circular wall and a second semi-circular wall opposite the first semi-circular wall, wherein each slot of the plurality of slots is defined by, at least, a length dimension and a width dimension, the length dimension being greater than the width dimension, wherein each slot of the plurality of slots is oriented such that the length dimension is substantially perpendicular to an expected direction of airflow through the gas turbine engine and over the slot, wherein the plurality of slots are configured to be oriented at an angle relative to a central longitudinal axis of the gas turbine engine, where the central longitudinal axis is different from the expected direction of airflow through the gas turbine engine, wherein the angle is defined by a centerline of each slot of the plurality of slots and the central longitudinal axis, wherein a first end of a first semi-circular wall of at least one first slot in the plurality of slots through the face skin is at least one of axially offset or circumferentially offset from a second end of a second semi-circular wall of the at least one first slot based upon a degree of a first angle, wherein a first end of a first semi-circular wall of at least one second slot in the plurality of slots through the face skin is at least one of axially offset or circumferentially offset from a second end of a second semi-circular wall of the at least one second slot based upon a degree of a second angle, wherein the first angle is different from the second angle, wherein the plurality of slots in the sheet comprises forming at least three regions with a first region of the sheet having a first percentage of open area and a first number of slots that is greater than a second percentage of open area and a second number of slots in a second region of the sheet and greater than a third percentage of open area and a third number of slots in a third region of the sheet, wherein the second percentage of open area and the second number of slots in the second region of the sheet is greater than the third percentage of open area and the third number of slots in the third region of the sheet, wherein a percentage of open area and a number of slots in each of the first region, the second region and the third region is selected based on an expected velocity of an airflow over a respective region and acoustic characteristics experienced in the respective region, and wherein the first number of slots is offset from the second number of slots.
2 . The face skin of claim 1 , wherein a ratio of a length of a first slot of the plurality of slots to a width of the first slot is between 2:1 and 10:1.
3 . The face skin of claim 1 , wherein a ratio of a length of a first slot of the plurality of slots to a radius of the first semi-circular wall of the first slot is about 2:1.
4 . The face skin of claim 1 , wherein the sheet comprises a fiber reinforced composite material.
5 . The face skin of claim 4 , wherein the fiber reinforced composite material comprises at least one of a fiberglass reinforced composite or a carbon fiber reinforced composite.