Low pressure ratio fan engine having a dimensional relationship between inlet and fan size

1. A gas turbine engine assembly, comprising:

a fan section including a fan and a fan case surrounding the fan to define a bypass duct, the fan including a plurality of fan blades having circumferentially outermost edges, a diameter of the fan having a dimension D extending between the circumferentially outermost edges of the fan blades, each fan blade having a leading edge, forward-most portion on the leading edges of the fan blades in a first reference plane, wherein a portion of the fan case is forward of the leading edges of the fan blades, and each of the fan blades is a three-dimensional swept fan blade twisted about a first axis extending in a radial direction between the circumferentially outermost edge and a root of the fan blade;

a geared architecture defining a gear reduction ratio or greater than 2.3, and wherein the geared architecture is a star gear system;

a compressor section including a low pressure compressor and a high pressure compressor;

a turbine section including a high pressure turbine and a low pressure turbine, the low pressure turbine driving the fan;

a nacelle including an inlet portion forward of the fan, a forward edge on the inlet portion in a second reference plane, and a length of the inlet portion having a dimension L measured along an engine central longitudinal axis between the first reference plane and the second reference plane;

wherein the fan delivers a portion of air into the compressor section and a portion of air into the bypass duct, and a bypass ratio of grater than 10, the bypass ratio being a ratio of a volume of air passing to the bypass duct compared to a volume of air passing into the compressor section;

an inner shaft concentric with an outer shaft, the inner and outer shafts rotatable about the engine central longitudinal axis, wherein the inner shaft connects the fan and the low pressure compressor to the low pressure turbine, the outer shaft interconnects the high pressure compressor to the high pressure turbine, and the inner shaft drives the fan through the geared architecture;

wherein the fan has a pressure ratio of between 1.20 and 1.50 across the fan blade alone at a cruise design point;

wherein a dimensional relationship of L/D is between 0.30 and 0.40; and

wherein the low pressure turbine includes an inlet, an outlet, and a pressure ratio of greater than 5:1, where the pressure ratio is pressure measured prior to the inlet as related to pressure measured at the outlet prior to any exhaust nozzle.

2. The assembly of claim 1 , wherein the high pressure turbine includes two stages.

3. The assembly of claim 2 , wherein the pressure ratio of the fan is less than 1.45 across the fan blade alone at the cruise design point.

4. The assembly of claim 2 , wherein the fan has a low corrected fan tip speed of less than 1150 ft/second.

5. The assembly of claim 4 , wherein the turbine section includes a mid-turbine frame between the high pressure turbine and the low pressure turbine.

6. The assembly of claim 5 , wherein the mid-turbine frame includes a plurality of vanes in a core airflow path defined by the turbine section.

7. The assembly of claim 6 , wherein the plurality of vanes are inlet guide vanes.

8. The assembly of claim 7 , wherein the inlet guide vanes set airflow entering the low pressure turbine during operation.

9. The assembly of claim 8 , wherein the dimensional relationship of L/D is 0.35.

10. The assembly of claim 9 , wherein:

the second reference plane is oriented at an oblique angle relative to the engine central longitudinal axis; and

the oblique angle is 5 degrees.

11. The assembly of claim 1 , wherein:

the turbine section includes a mid-turbine frame between the high pressure turbine and the low pressure turbine; and

the mid-turbine frame supports bearing systems.

12. The assembly of claim 11 , wherein the mid-turbine frame includes a plurality of vanes in a core airflow path defined by the turbine section.

13. The assembly of claim 12 , wherein:

the plurality of vanes are inlet guide vanes; and

the inlet guide vanes set airflow entering the low pressure turbine during operation.

14. The assembly of claim 1 , wherein the fan has a low corrected fan tip speed of less than 1150 ft/second.

15. The assembly of claim 14 , wherein the pressure ratio of the fan is less than 1.45 across the fan blade alone at the cruise design point.

16. The assembly of claim 1 , wherein the pressure ratio of the fan is less than 1.45 across the fan blade alone at the cruise design point.

17. The assembly of claim 16 , wherein:

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

18. The assembly of claim 17 , wherein:

the high pressure turbine includes two stages.