Acoustic liner with obliquely angled slots
An acoustic liner for a gas turbine engine includes an acoustic panel that is curved about a central axis. The acoustic panel includes a support backing, a face sheet, and a cellular structure disposed between the support backing and the face sheet. The face sheet has elongated slots that extend along respective slot centerlines in the plane of the face sheet. The slot centerlines are sloped at oblique angles to the central axis.
1. An acoustic liner for a gas turbine engine, comprising:
an acoustic panel that is curved about a central axis, the acoustic panel including, a support backing,
a face sheet having a radially inner face, and
a cellular structure disposed between the support backing and the face sheet,
the face sheet having elongated slots that are elonagted along respective slot centerlines, the slot centerlines being in the plane of the radially inner surface of the face sheet, the slot centerlines being sloped at oblique angles to the central axis, wherein the face sheet varies in hardness.
2. The acoustic liner as recited in claim 1 , wherein each said elongated slot defines a slot length (L) and a slot width (W), and a ratio of L to W is from 2 to 10.
3. The acoustic liner as recited in claim 1 , wherein the elongated slots are arranged in multiple circumferential rows.
4. The acoustic liner as recited in claim 1 , wherein each said elongated slot defines a slot width (W), the elongated slots define a slot-to-slot spacing (S), and a ratio of S to W is from 2 to 10.
5. The acoustic liner as recited in claim 1 , wherein the elongated slots are linear.
6. The acoustic liner as recited in claim 1 , wherein the elongated slots are parallel to each other.
7. The acoustic liner as recited in claim 1 , wherein the oblique angles are from 37° to 65°.
8. The acoustic liner as recited in claim 1 , wherein each said elongated slot defines a slot length (L) and a slot width (W), a ratio of L to W is from 2 to 10, the elongated slots are arranged in multiple circumferential rows, the elongated slots define a slot-to-slot spacing (S), and a ratio of S to W is from 2 to 10.
9. The acoustic liner as recited in claim 1 , wherein each said elongated slot defines a slot width (W), said face sheet defines a thickness (T), said width (W) is from 0.005 to 0.07 inches, and said thickness (T) is from 0.02 to 0.1 inches.
10. The acoustic liner as recited in claim 1 , wherein said elongated slots are arranged in adjacent slot patterns, each said elongated slot defines a slot width (W), each one of said adjacent slot patterns defines a minimum pattern-to-pattern gap (G), and a ratio of said pattern-to-pattern gap (G) to said slot width (W) is 2 or greater.
11. The acoustic liner as recited in claim 1 , wherein each of the elongated slots defines a slot thickness, a slot width, and a slot length, the slot length is greater than each of the slot thickness and the slot width, and the centerlines are taken along the slot lengths.
12. A gas turbine engine, comprising:
a fan operable to rotate in a rotational direction about a central engine axis to provide propulsion;
a fan case surrounding the fan, the fan case including an acoustic liner downstream of the fan and having one or more acoustic panels, the one or more acoustic panels being curved about the central engine axis, wherein each said acoustic panel includes,
a support backing,
a face sheet, and
a cellular structure disposed between the support backing and the face sheet, the face sheet having slots extending along respective slot centerlines in the plane of the face sheet and collectively having a slot texture, each said slot defining an axially aft slot end and an axially forward slot end, the axially forward slot end being circumferentially forward of the axially aft slot end relative to the rotational direction of the fan, a directionality along the slot centerlines from the axially forward slot end to the axially aft slot end, the directionality defining the slot texture, wherein the rotational direction of the fan is against the directionality of the slot texture.
13. The gas turbine engine as recited in claim 12 , wherein each said slot defines an axially aft slot end and an axially forward slot end, the axially forward slot end being circumferentially forward of the axially aft slot end relative to the rotational direction of the fan, each said slot is elongated and defines a slot length (L) and a slot width (W), a ratio of L to W is from 2 to 10, the slots are arranged in multiple circumferential rows, the slots define a slot-to-slot spacing (S), and a ratio of S to W is from 2 to 10.
14. The gas turbine engine as recited in claim 12 , wherein the face sheet varies in hardness.
15. A method of fabricating a face sheet for an acoustic liner, the method comprising:
forming a face sheet by additive manufacturing, wherein the face sheet has a radially inner surface that is curved about a central axis and that has elongated slots that are elongated along respective slot centerlines in the plane of the radially inner surface of the face sheet, wherein the slot centerlines are sloped at oblique angles to the central engine axis and the additive manufacturing uses polymers of different hardnesses such that the face sheet varies in hardness.
16. The method as recited in claim 15 , wherein the face sheet is formed on a cellular structure and the slot centerlines are sloped at oblique angles to the central axis.
17. The method as recited in claim 16 , wherein the elongated slots are formed in alignment with cells of the cellular structure.
18. The method as recited in claim 16 , wherein the face sheet is fused directly to the cellular structure without an adhesive.