gruntguru wrote:Axial and centrifugal compressors are "rotodynamic" machines. This means they work by accelerating the air to a high velocity (kinetic energy) then convert that KE to pressure by slowing it down again in a diffuser. In broad terms the PR of each stage is limited by the velocity ratio of the outlet to inlet of the rotating part (impeller).
It is obvious immediately that a centrifugal compressor impeller has a relatively slow inlet and much higher velocity outlet - being placed much further from the axis of rotation.
Axial compressors achieve a velocity difference through blade shape. At the intake side the blades are slicing through the air as it approaches roughly axially (small tangential velocity component). As the air passes along the blade, it is turned to rotate in the same direction as the rotating impeller so it now has a large tangential velocity component in addition to its axial (flow) component. It should be clear that the potential for achieving a large velocity ratio is much less for the axial compressor. If higher pressures are required, it is necessary to slow the air down in a diffuser (stationary vanes) and repeat the process in another stage.
Do you have an equation? Based on some of the schematics shared, that may not be the case if it is, a radial compressor still has waste gates, which is to say excess pressure.