I'm surprised no-one has yet mentioned expansion ratio, rather than compression ratio (at least I don't think it was mentioned). The work output comes from the expansion of the gases, not the compression
Isn't the expansion limited by the atmosphereric pressure and thus has only small variations?
It would seem that the imput pressure is what varries the most, so in what way does the term of using the expansion ratio differ from the compression ratio in a gas turbine?
We really do need to corral this discusion around gas velocities in a turbine, other wise we wouldn't have a compressor and a means of expansion across a turbine stage or an exhaust jet pipe