Geared gas turbine engine with reduced fan noise

1. A gas turbine engine comprising:

a fan section having a plurality of fan blades, said plurality being equal to or less than 26, said fan section having a low fan pressure ratio of less than 1.45, wherein the low fan pressure ratio is measured across one of said fan blades alone;

a geared arrangement that drives said fan section;

a compressor section including a first compressor section and a second compressor section;

a turbine section including a first turbine section that drives said first compressor section, and a second turbine section that drives said second compressor section and said geared arrangement with said geared arrangement providing a gear reduction;

a plurality of exit guide vanes positioned downstream of said fan blades;

wherein a first ratio of a number of exit guide vanes to a number of fan blades being between 0.8 and 2.0; and

wherein said exit guide vanes are provided with sweep and lean,

wherein sweep means that: (a) an outer periphery of said exit guide vane is positioned to be downstream of a location of an inner periphery of said exit guide vane; and (b) a sweep angle is between 20 degrees and 30 degrees, and

wherein lean means that: (a) an outer periphery of said exit guide vane is positioned at a greater circumferential distance than an inner periphery of said exit guide vane in a direction of rotation of said fan blades; and (b) a lean angle is greater than or equal to 2 degrees and less than or equal to 15 degrees.

2. The gas turbine engine as set forth in claim 1 , wherein:

said geared arrangement has a gear reduction ratio greater than or equal to 2.3;

wherein the second turbine section includes an inlet, an outlet and a pressure ratio of greater than 5, the pressure ratio being pressure measured prior to the inlet as related to pressure at the outlet prior to an exhaust nozzle; and

wherein the fan has a low corrected fan tip speed of less than 1150 ft/second.

3. The gas turbine engine as set forth in claim 2 , wherein:

each of said exit guide vanes defines a hollow opening covered by an acoustic liner having a perforated face sheet;

said face sheet has a thickness, and a diameter of holes in said face sheet is selected to be less than or equal 0.3 of the thickness.

4. The gas turbine engine as set forth in claim 3 , wherein said holes in said face sheet are at least 5% of a surface area of said face sheet.

5. The gas turbine engine as set forth in claim 4 , wherein said diameter is less than or equal to 0.2 of the thickness.

6. The gas turbine engine as set forth in claim 1 , wherein:

each of said exit guide vanes defines a hollow opening covered by an acoustic liner having a perforated face sheet;

said face sheet has a thickness, and a diameter of holes in said face sheet is selected to be less than or equal 0.3 of the thickness.

7. The gas turbine engine as set forth in claim 6 , wherein said holes in said face sheet are at least 5% of a surface area of said face sheet.

8. The gas turbine engine as set forth in claim 7 , wherein said diameter is less than or equal to 0.2 of the thickness.

9. A gas turbine engine comprising:

a fan section having a plurality of fan blades, said fan section having a low fan pressure ratio of less than 1.45, wherein the low fan pressure ratio is measured across one of said fan blades alone;

a geared arrangement that drives said fan section;

a compressor section including a first compressor section and a second compressor section;

a turbine section including a first turbine section that drives said first compressor section, and a second turbine section that drives said second compressor section and said geared arrangement;

a plurality of exit guide vanes positioned downstream of said fan blades;

wherein a first ratio of a number of exit guide vanes to a number of fan blades being between 0.8 and 2.0;

wherein said exit guide vanes are provided with sweep and lean,

wherein sweep means that: (a) an outer periphery of said exit guide vane is positioned to be downstream of a location of an inner periphery of said exit guide vane; and (b) a sweep angle is between 5 degrees and 35 degrees,

wherein lean means that: (a) an outer periphery of said exit guide vane is positioned at a greater circumferential distance than an inner periphery of said exit guide vane in a direction of rotation of said fan blades; and (b) a lean angle is greater than or equal to 2 degrees and less than or equal to 15 degrees; and

said geared arrangement has a gear reduction ratio greater than or equal to 2.3;

wherein the second turbine section includes an inlet, an outlet and a pressure ratio of greater than 5, the pressure ratio being pressure measured prior to the inlet as related to pressure at the outlet prior to an exhaust nozzle; and

wherein the fan has a low corrected fan tip speed of less than 1150 ft/second.

10. The gas turbine engine as set forth in claim 9 , wherein said sweep angle is greater than or equal to 20 degrees.

11. The gas turbine engine as set forth in claim 10 , wherein said fan section has 26 or fewer fan blades.

12. The gas turbine engine as set forth in claim 11 , wherein:

each of said exit guide vanes defines a hollow opening covered by an acoustic liner having a perforated face sheet;

said face sheet has a thickness, and a diameter of holes in said face sheet is selected to be less than or equal to 0.3 of the thickness; and

holes in said face sheet are at least 5% of a surface area of said face sheet.

13. The gas turbine engine as set forth in claim 9 , wherein said fan section has 26 or fewer fan blades.

14. The gas turbine engine as set forth in claim 13 , wherein:

each of said exit guide vanes defines a hollow opening covered by an acoustic liner having a perforated face sheet;

said face sheet has a thickness, and a diameter of holes in said face sheet is selected to be less than or equal to 0.3 of the thickness; and

holes in said face sheet are at least 5% of a surface area of said face sheet.

15. The gas turbine engine as set forth in claim 14 , wherein said diameter is less than or equal to 0.2 of the thickness.

16. The gas turbine engine as set forth in claim 9 , wherein:

each of said exit guide vanes defines a hollow opening covered by an acoustic liner having a perforated face sheet;

said face sheet has a thickness, and a diameter of holes in said face sheet is selected to be less than or equal to 0.3 of the thickness; and

holes in said face sheet are at least 5% of a surface area of said face sheet.

17. The gas turbine engine as set forth in claim 14 , wherein said diameter is less than or equal to 0.2 of the thickness.

18. The gas turbine engine as set forth in claim 9 , wherein:

each of said exit guide vanes defines a hollow opening covered by an acoustic liner having a perforated face sheet;

said face sheet has a thickness, and a diameter of holes in said face sheet is selected to be less than or equal 0.3 of the thickness.

19. The gas turbine engine as set forth in claim 18 , wherein said diameter is less than or equal to 0.2 of the thickness.

20. The gas turbine engine as set forth in claim 9 , wherein said geared arrangement is between said fan section and said second turbine section.

21. A gas turbine engine comprising:

a fan section having a plurality of fan blades;

a geared arrangement that drives said fan section;

a compressor section including a first compressor section and a second compressor section;

a turbine section including a first turbine section that drives said first compressor section, and a second turbine section that drives said second compressor section and said geared arrangement;

a plurality of exit guide vanes positioned downstream of said fan blades;

wherein a first ratio of a number of exit guide vanes to a number of fan blades being between 0.8 and 2.0;

wherein said exit guide vanes are provided with sweep and lean,

wherein sweep means that: (a) an outer periphery of said exit guide vane is positioned to be downstream of a location of an inner periphery of said exit guide vane; and (b) a sweep angle is between 20 degrees and 35 degrees,

wherein lean means that: (a) an outer periphery of said exit guide vane is positioned at a greater circumferential distance than an inner periphery of said exit guide vane in a direction of rotation of said fan blades; and (b) a lean angle is greater than 2 degrees and less than or equal to 15 degrees; and

each of said exit guide vanes defines a hollow opening covered by an acoustic liner having a perforated face sheet;

said face sheet has a thickness, and a diameter of holes in said face sheet is selected to be less than or equal to 0.3 of the thickness; and

holes in said face sheet are at least 5% of a surface area of said face sheet.

22. The gas turbine engine as set forth in claim 21 , wherein said fan section has 26 or fewer fan blades.

23. The gas turbine engine as set forth in claim 22 , wherein:

said geared arrangement has a gear reduction ratio greater than or equal to 2.3;

wherein the second turbine section includes an inlet, an outlet and a pressure ratio of greater than 5, the pressure ratio being pressure measured prior to the inlet as related to pressure at the outlet prior to an exhaust nozzle; and

wherein the fan has a low corrected fan tip speed of less than 1150 ft/second.

24. The gas turbine engine as set forth in claim 23 , wherein said diameter is less than or equal to 0.2 of the thickness.

25. The gas turbine engine as set forth in claim 22 , wherein:

said geared arrangement has a gear reduction ratio greater than or equal to 2.3;

wherein the second turbine section includes an inlet, an outlet and a pressure ratio of greater than 5, the pressure ratio being pressure measured prior to the inlet as related to pressure at the outlet prior to an exhaust nozzle; and

wherein the fan has a low corrected fan tip speed of less than 1150 ft/second.

26. The gas turbine engine as set forth in claim 21 , wherein:

said geared arrangement has a gear reduction ratio greater than or equal to 2.3;

wherein the second turbine section includes an inlet, an outlet and a pressure ratio of greater than 5, the pressure ratio being pressure measured prior to the inlet as related to pressure at the outlet prior to an exhaust nozzle.

27. The gas turbine engine as set forth in claim 26 , wherein said diameter is less than or equal to 0.2 of the thickness.

28. The gas turbine engine as set forth in claim 21 wherein said sweep angle is less than or equal to 25 degrees.

29. The gas turbine engine as set forth in claim 28 , wherein said diameter is less than or equal to 0.2 of the thickness.

30. The gas turbine engine as set forth in claim 21 , wherein said diameter is less than or equal to 0.2 of the thickness.