On a axial flow turbo fan or turbo jet engine what comes first the rotor or the stator?
There are two aspects to consider here:


The aerodynamic principle:

The simple aerodynamic principle requires a compressor stage to have first a rotor followed by a stator.
The constructive aspects:

Constructive aspects to be considered are:

a) Pre-rotation of air before the rotor: in order to reduce the relative speed of the airflow on the rotor blades (to avoid the shock waves of supersonic airflow) a set of stators can be placed in front of the rotor; this will rotate the air towards the direction of rotation, reducing by this the relative speed of the airflow on the rotor blades; even in such cases a stator stage is required after the rotor.

b) Bearing location: some designs put the bearing behind the rotor, other designs put the bearing in front of the rotor; in such case the bearing before the rotor needs to be supported by a system of vanes.


Consequently, many smaller diameter (or high speed military design) engines will take advantage of a) and b) above and have a stator in front of the first stage compressor.

To answer the same questions on turbines, there the aerodynamic principle requires to have first a set of stators and then a rotor.