Centrifugal compressor diffuser passage boundary layer control

A centrifugal compressor diffuser (42) includes a plurality of diffuser flow passages (22) extending through an annular diffuser housing (20) and circumferentially bounded by diffuser vanes (23) and axially bounded by forward and aft walls (101, 100). A diffuser boundary layer bleed (96) for the passages may include boundary layer bleed apertures (106) or slots (130) disposed through the forward wall (101) and a downstream facing wall (142) canted at an acute cant angle to a downstream diffuser airflow direction (103) in the passages. Diffuser bleed flow (112) is bled from a diffuser boundary layer. Boundary layer bleed apertures can be located downstream of throat sections (28) of the flow passages near pressure sides of the vanes. A centrifugal compressor (18) may include the diffuser surrounding an annular centrifugal compressor impeller (32) and apparatus for flowing impeller bleed flow (102) from a radial clearance between an impeller tip (36) and a diffuser annular inlet (27) with diffuser bleed flow ei