High bypass turbo fans like airliners do get a significant bit of the compression from the forward momentum. They will never be able to function like ram jets, but the momentum makes a big difference especially at high altitude where the air is less dense and there isn't as much to suck in from the fans/compressors alone. The high bypass engines of the airliners will function much more efficiently at high altitude because of this than that of a low bypass military fighter, however it won't be able to achieve as high of a top speed as that same fighter under the same conditions. Basically the low bypass gets the advantage of speed while the high bypass gets the advantage of fuel efficiency, but both greatly benefit from momentum based compression.