The Wikipedia article on the Pratt & Whitney F119 that powers the F-22 says the following:
- The high pressure and low pressure turbines are single stage and counter-rotating, thus shortening the engine and saving weight.
- Turbine: Counter-rotating 1-stage high-pressure, 1-stage low-pressure turbines
- Type: Twin-spool, axial flow augmented turbofan
We also find:
Thrust augmentation is using additional fuel in a turbofan's cold bypass air only, instead of the combined cold and hot gas flows as in a conventional afterburning engine.— Afterburner
- What's the benefit of lighting the bypass air compared to relighting the exhaust? Wouldn't the cooling benefits of the bypass air be lost?
- Does that mean that the F-22's "supercruising" could be "augmented"?
- How does by counter-rotating the two-spools, the engine becomes shorter and lighter?
- How are the turbines counter-rotated?
While the answers are probably buried deep in the Integrated High Performance Turbine Engine Technology program, hopefully some educated guesses can entertain my curiosity.
My only guess for 4. is the use of aggressively curved and converging stators, which would otherwise stall a normal none counter-rotating LP turbine. Or perhaps the lack of a stator in the turbine section, since it's a single LP stage, which would also answer 3.