Gas turbine engine rotor casing treatment

1. An annular casing for a rotor of a gas turbine engine, the annular casing comprising:

an annular casing wall having a casing treatment, an inner surface of the annular casing wall surrounding a flow path, the casing treatment including:

a recess extending radially outwardly from the inner surface of the annular casing wall, the recess circumferentially bounded by a recessed surface radially outwardly offset from the inner surface;

at least one groove defined in the annular casing wall and extending radially outwardly from the recessed surface, the at least one groove having an open end defined in the recessed surface and an opposed closed end; and

a perforated sheet disposed in the recess and overlapping the open end of the at least one groove, the perforated sheet abutting against the recessed surface and extending radially inwardly from the recessed surface, the perforated sheet including a plurality of apertures extending through a thickness of the perforated sheet, the plurality of apertures providing fluid communication between the at least one groove and the flow path.

2. The casing of claim 1 , wherein the at least one groove is a circumferential groove.

3. The casing of claim 1 , wherein the perforated sheet is an annular sheet.

4. The casing of claim 1 , wherein the plurality of apertures extend along a radial direction of the casing wall.

5. The casing of claim 1 , wherein the plurality of apertures extend at a non-zero angle relative to a radial direction of the casing wall.

6. The casing of claim 1 , wherein the perforated sheet is monolithic.

7. The casing of claim 1 , wherein the perforated sheet overlaps a plurality of the at least one groove, a plurality of protrusions being defined in the casing wall between adjacent grooves of the plurality of the grooves, and the perforated sheet contacts the plurality of protrusions.

8. A gas turbine engine comprising:

a rotor having a plurality of blades extending in a flow path, each blade having a blade tip; and

an annular casing wall surrounding the rotor and spaced from each blade tip by a clearance, the annular casing wall having a casing treatment, an inner surface of the annular casing wall surrounding the flow path, the casing treatment including:

a recess extending radially outwardly from the inner surface of the annular casing wall, the recess circumferentially bounded by a recessed surface radially outwardly offset from the inner surface;

at least one groove defined in the annular casing wall and extending radially outwardly from the recessed surface, an open end of the at least one groove defined in the recessed surface, the at least one groove having a closed end opposite to the open end thereof; and

a perforated sheet disposed in the recess between the at least one groove and each blade tip, the perforated sheet abutting against the recessed surface and extending radially inwardly from the recessed surface, the perforated sheet including a plurality of apertures extending through a thickness of the perforated sheet and providing fluid communication between the at least one groove and the flow path.

9. The gas turbine engine of claim 8 , wherein the perforated sheet is annular.

10. The gas turbine engine of claim 8 , wherein the at least one groove is a circumferential groove.

11. The gas turbine engine of claim 8 , wherein the plurality of apertures extend along a radial direction of the annular casing wall.

12. The gas turbine engine of claim 8 , wherein the plurality of apertures extend at a non-zero angle relative to a radial direction of the annular casing wall.

13. The gas turbine engine of claim 8 , wherein the rotor is a compressor rotor.

14. A method of reducing flow losses in a casing treatment of a wall of a casing disposed around rotatable blades of a gas turbine engine, the method comprising:

covering at least a portion of the casing treatment with a perforated sheet inserted in a recess extending radially outwardly from an inner surface of the wall to a recessed surface, the perforated sheet abutting against the recessed surface circumferentially bounding the recess and radially outwardly offset from the inner surface, the perforated sheet extending radially inwardly from the recessed surface, the perforated sheet in fluid communication with the portion of the casing treatment, the casing treatment comprising at least one groove having a closed bottom end.

15. The method of claim 14 , further comprising directing a flow radially outwardly of tips of the blades through the perforated sheet surrounding the blades, directing the flow from the perforated sheet into the at least one groove of the casing treatment, the at least one groove extending radially outwardly of the perforated sheet, and directing at least part of the flow from the at least one groove back through the perforated sheet.

16. The method of claim 15 , wherein directing the flow through the perforated sheet comprises directing the flow through a plurality of apertures extending through a thickness of the perforated sheet.