Actually, with most gas turbines, once you are past the fan and entering the core engine, there is a row of inlet guide vanes before the first compressor stage. In many turbines these IGV's are also adjustable and vary with compressor speed. Their job is to present the air at a suitable angle to the first compressor stage (a 'stage' being a rotating set of blades and a stationary set of vanes), this angle to ensure that the angle between the flow and the rotating blade is held below the stalling angle of the blades. As the speed and flow is variable, then the guide vanes (and often the stationary vanes too, known as Variable Stator Vanes, VSV's) modulate within a set of parameters to maintain flow through the compressor. So it could be said that these IGV's set up a spiral airflow for the compressor. Of course the blades then spiral the air the other way, the next stator back again, etc. The net flow is almost straight.
Evan, WB #12