I have read online that a gas turbine converts the chemical energy in the fuel gas to mechanical energy of the turbine blades. The way I see it, because of this hot air one would have to go for heat recovery and use costlier heat resistant material in the turbine. So instead why not send the compressed air directly through the turbine blades?
As an example, in wind turbines I understand we try to work on factors to improve the wind speed which in turn would mean more mechanical energy of the blades and in turn more electricity. I am trying to understand the purpose of the combustor similarly. Thanks for your help!