Adaptive fan reverse core geared turbofan engine with separate cold turbine

1. A turbine engine comprising:

a first fan including a plurality of fan blades rotatable about an axis;

a reverse flow core engine section including a core turbine axially forward of a combustor and a compressor, the core turbine driving the compressor about the axis;

a transmission driven by the core turbine;

a geared architecture driven by the transmission system for driving the first fan at a speed less than the core turbine;

a second fan disposed axially aft of the first fan and forward of the core engine; and

a second turbine disposed between the second fan and the core engine, the second turbine driving the second fan, wherein the transmission includes a first mode wherein the second fan is coupled to the transmission and driven at a speed of the core turbine, and wherein the transmission includes a second mode wherein the second fan is driven at a speed less than that of the core turbine and greater than that of the first fan.

2. The turbine engine as recited in claim 1 , wherein the second fan and second turbine are fixed to rotate at a common speed.

3. The turbine engine as recited in claim 2 , wherein the second turbine drives the second fan responsive to the transmission decoupling from the second fan.

4. The turbine engine as recited in claim 3 , including a variable vane disposed axially forward of the second turbine for controlling a speed of the second turbine and thereby the second fan.

5. The turbine engine as recited in claim 1 , wherein the transmission includes a first transmission path coupling the core turbine to the second fan and the geared architecture such that second fan rotates at a speed common with the core turbine.

6. The turbine engine as recited in claim 5 , wherein the transmission includes a second transmission path through a gear reduction to drive the second fan at a speed less than that of the core turbine and greater than the first fan.

7. A method of operating a turbine engine comprising

defining a core gas flow path through a core engine, where the core engine includes a compressor, a combustor in communication with the compressor and a core turbine driven by high energy gas flow generated by the combustor;

driving a transmission with the core turbine;

driving a first fan through a geared architecture driven by the transmission;

driving a second fan axially aft of the first fan and forward of the core turbine, wherein the second fan is driven by the transmission at a speed common with the core turbine in a first mode; and

driving the second fan with a second turbine disposed axially forward of the core turbine when the transmission is in a second mode, wherein in the second mode the second fan is driven at a speed less than that of the core turbine and greater than that of the first fan.

8. The method as recited in claim 7 , wherein the second fan and second turbine are fixed to rotate at a common speed and speed of the second turbine is varied to change the speed of the second fan when decoupled from the transmission.

9. The method as recited in claim 7 , wherein the second turbine drives the second fan responsive to the transmission decoupling from the second fan.

10. The method as recited in claim 7 , wherein the transmission includes a first transmission path coupling the core turbine to the second fan and the geared architecture such that second fan rotates at a speed common with the core turbine in the first mode.

11. The method as recited in claim 10 , wherein the transmission includes a second transmission path through a gear reduction to drive the second fan at a speed less than that of the core turbine and greater than the first fan in the second mode.