Thrust efficient turbofan engine

1. A turbofan engine comprising:

a propulsor section, the propulsor section having a fan and a core flow path portion, the fan having a number of fan blades that have a fan tip diameter greater than 50 inches and less than 160 inches;

a low spool having an inner shaft and a power turbine including from three to six rotors, wherein a ratio between the number of fan blades and a number of power turbine rotors is between 3.3 and 8.6;

a high spool having an outer shaft concentric about the inner shaft;

a geared architecture in driving connection between the power turbine and the fan, wherein the geared architecture has a gear ratio greater than 2.3; and

an Engine Unit Thrust Parameter (“EUTP”) defined as net engine thrust divided by a product of the mass flow rate of air through a bypass flow path, the fan tip diameter of the fan and a first rotational speed of the power turbine, the EUTP is less than 0.30 in operation at a maximum takeoff thrust;

wherein the turbofan engine is capable of generating a propulsive thrust between 16,000 lbf and about 120,000 lbf, the mass flow rate of air through the bypass flow path is between 625 Ibm/sec and 80,000 Ibm/sec and the first rotational speed is between 6,200 rpm and 12,500 rpm.

2. The turbofan engine as recited in claim 1 , wherein the fan includes less than 20 fan blades.

3. The turbofan engine as recited in claim 2 , further comprising a low fan pressure ratio across the fan alone that is less than 1.45 in operation.

4. The turbofan engine as recited in claim 3 , further comprising a two-stage high pressure turbine and wherein the geared architecture is a planetary gear system and the fan rotates at a fan tip speed less than 1150 ft/sec in operation.

5. The turbofan engine as recited in claim 4 , further comprising a gas generator section, the gas generation section including the core flow path portion of the propulsor section, a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a part of the power turbine, the gas generator having an overall pressure ratio between entering airflow into the gas generator and exiting gas stream from the gas generator that is between 40 and 80 in operation.

6. The turbofan engine as recited in claim 3 , wherein the EUTP in operation at the maximum takeoff thrust is less than 0.25.

7. The turbofan engine as recited in claim 6 , wherein the EUTP in operation at the maximum takeoff thrust is less than 0.20.

8. The turbofan engine as recited in claim 7 , wherein the power turbine has a pressure ratio greater than 5 measured prior to an inlet to the power turbine as related to a pressure measured at an outlet of the power turbine prior to any exhaust nozzle.

9. The turbofan engine as recited in claim 8 , wherein the EUTP in operation at one of a climb condition and a cruise condition is less than 0.15.

10. The turbofan engine as recited in claim 9 , wherein the EUTP in operation at a cruise condition is less than 0.08.

11. The turbofan engine as recited in claim 10 , wherein the EUTP in operation at a climb condition is less than 0.08.

12. The turbofan engine as recited in claim 11 , further comprising a gas generator section, the gas generation section including the core flow path portion of the propulsor section, a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a part of the power turbine, the gas generator having an overall pressure ratio between entering airflow into the gas generator and exiting gas stream from the gas generator that is between 40 and 80 in operation.

13. The turbofan engine as recited in claim 11 , wherein the EUTP in operation at the maximum takeoff thrust is less than 0.15.

14. The turbofan engine as recited in claim 13 , wherein the fan rotates at a fan tip speed less than 1150 ft/sec in operation, and the EUTP in operation at the maximum takeoff thrust is less than 0.10.

15. The turbofan engine as recited in claim 1 , wherein the EUTP is less than 0.10 in operation at a maximum takeoff thrust.

16. The turbofan engine as recited in claim 5 , wherein the EUTP in operation at a cruise condition is less than 0.08 and at the maximum takeoff thrust is less than 0.15.

17. A turbofan engine comprising:

a power turbine including from three to six rotors;

a geared architecture in driving connection between the power turbine and a fan, wherein the geared architecture has a gear ratio greater than 2.3;

a propulsor section, the propulsor section having the fan and a core flow path portion, the fan having a fan tip diameter between 45 inches and 160 inches; and

a low fan pressure ratio across the fan alone that is less than 1.45 in operation; wherein an Engine Unit Thrust Parameter (“EUTP”) is defined as net engine thrust divided by a product of the mass flow rate of air through a bypass flow path, the fan tip diameter of the fan and a first rotational speed of the power turbine and in operation is less than 0.30 at a sea level takeoff power condition, wherein the net engine thrust is between 16,000 lbf and 120,000 lbf, the mass flow rate of air through the bypass flow path is between 625 Ibm/sec and 80,000 Ibm/sec and the first rotational speed is between 6,200 rpm and 12,500 rpm.

18. The turbofan engine as recited in claim 17 , wherein the fan rotates at a fan tip speed less than 1150 ft/sec in operation.

19. The turbofan engine as recited in claim 18 , further comprising a gas generator section, the gas generation section including the core flow path portion of the propulsor section, a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a part of the power turbine, the gas generator having an overall pressure ratio between entering airflow into the gas generator and exiting gas stream from the gas generator that is between 40 and 80 in operation.

20. The turbofan engine as recited in claim 19 , wherein the fan includes less than 20 fan blades.

21. The turbofan engine as recited in claim 20 , wherein the EUTP in operation at the sea level takeoff power condition is less than 0.20.

22. The turbofan engine as recited in claim 21 , wherein the EUTP in operation at the sea level takeoff power condition is less than 0.25.

23. The turbofan engine as recited in claim 22 , wherein the EUTP in operation at a cruise condition is less than 0.15.

24. The turbofan engine as recited in claim 23 , wherein a ratio between the number of fan blades and the number of rotors in the power turbine is between 3.3 and 8.6 and the EUTP in operation at the cruise condition is less than 0.08.

25. The turbofan engine as recited in claim 24 , wherein the EUTP in operation at a climb condition is less than 0.08.

26. The turbofan engine as recited in claim 25 , wherein the EUTP in operation at the sea level takeoff power condition is less than 0.15.

27. The turbofan engine as recited in claim 26 , wherein the high pressure turbine is a two stage high pressure turbine.

28. The turbofan engine as recited in claim 27 , wherein the EUTP in operation is greater or equal to 0.05 at a cruise condition.