9.4 Centrifugal-Flow Compressor Analysis

The centrifugal compressor has been around for many years. It was used in turbochargers before being used in the first turbojet engines of Whittle and von Ohain. Figure 9.43 shows a sketch of a centrifugal-flow compressor with radial rotor (or impeller) vanes. Flow passes through the annulus between r _{1 h} and r _{1 t} at station 1 and enters the inducer section of the rotor (also called rotating guide vanes). Flow leaves the rotor at station 2 through the cylindrical area of radius r ₂ and width b. The flow then passes through the diffuser, where it is slowed and then enters the collector scroll at station 3.

Figure 9.43: Centrifugal-flow compressor.

The velocity diagrams at the entrance and exit of the rotor (impeller) are shown in Fig. 9.44. The inlet flow is assumed to be axial of uniform velocity u ₁. The relative flow angle of the flow entering the rotor increases from hub to tip and thus the twist of the inlet to the inducer section of the rotor. The flow leaves the rotor with a radial component of velocity w ₂ that is approximately equal to the inlet axial velocity u ₁ and a swirl (tangential) component of velocity v ₂ that is about 90% of the rotor velocity U _t. The diffuser (which may be vaneless) slows the velocity of the flow v ₃ to about 90 m/s (300 ft/s).