Acoustic treatment in an unducted area of a geared turbomachine

1. A geared turbomachine assembly, comprising:

a fan cowl housing a fan that is driven by a geared architecture;

a core cowl housing a core engine;

a low-pressure turbine section of the core engine that is axially spaced downstream from the fan cowl and axially downstream from the fan cowl; and

an acoustic treatment establishing a portion of the core cowl aft the fan cowl, wherein a portion of the acoustic treatment is axially aligned with a portion of a high-pressure turbine section of the geared turbomachine assembly that is axially aft the fan cowl relative to a direction of flow through the geared turbomachine.

2. The geared turbomachine assembly of claim 1 , wherein, at a given axial section, the acoustic treatment forms the core cowl.

3. The geared turbomachine assembly of claim 2 , wherein the acoustic treatment extends axially to an aftmost end of the core cowl.

4. The geared turbomachine assembly of claim 2 , wherein the acoustic treatment extends continuously from a position that is axially aligned with the fan cowl to an aftmost end of the core cowl.

5. The geared turbomachine assembly of claim 1 , wherein the acoustic treatment comprises a perforated face sheet having an open area density that is from 4% to 30%.

6. The geared turbomachine assembly of claim 1 , wherein the acoustic treatment comprises a microperforated face sheet having apertures with a diameter that is less than 25 percent of a thickness of the microperforated face sheet.

7. The geared turbomachine assembly of claim 1 , wherein the geared turbomachine assembly has a fan pressure ratio less than 1.45.

8. The geared turbomachine assembly of claim 1 , wherein the portion of the core cowl established by the acoustic treatment provides a radially inner boundary of a bypass flowpath.

9. The geared turbomachine assembly of claim 1 , wherein the acoustic treatment extends continuously from a position that is axially aligned with the fan cowl to a position that is axially aligned with the low-pressure turbine section of the geared turbomachine.

10. The geared turbomachine assembly of claim 1 , wherein the portion of the core cowl established by the acoustic treatment provides a radially outer boundary of a core engine flowpath of the geared turbomachine.

11. A geared turbomachine assembly, comprising:

a fan cowl distributed circumferentially about a fan that is driven by a geared architecture;

a core cowl distributed circumferentially about a core engine;

a low-pressure turbine section of the core engine that is axially spaced downstream from the fan cowl and axially downstream from the fan cowl; and

an acoustic treatment establishing a portion of the core cowl aft the fan cowl, wherein a portion of the acoustic treatment is axially aligned with a portion of a high-pressure turbine section of the geared turbomachine assembly that is axially aft the fan cowl relative to a direction of flow through the geared turbomachine,

wherein the portion of the core cowl established by the acoustic treatment provides a radially inner boundary of a bypass flowpath and further provides a radially outer boundary of a core engine flowpath.

12. The geared turbomachine assembly of claim 11 , wherein the acoustic treatment extends continuously from a position that is axially aligned with the fan cowl to a position that is axially aligned with the low-pressure turbine section, and from the position that is axially aligned with the low-pressure turbine section to an aftmost end of the core cowl.

13. The geared turbomachine assembly of claim 12 , wherein the geared turbomachine assembly has a fan pressure ratio less than 1.45.