Circumferential Nonuniformity of Rotor Outlet Flow in Axial Compressors

The rotor outlet flow in axial compressors is inherently circumferentially nonuniform, which challenges accurate interstage performance measurements. In practical compressors, small blade passages and limited probe access often restrict measurements to a single radial line, leaving the representativeness of the measured parameters uncertain. This study uses steady five-hole probes on a low-speed, large-scale axial-compressor rig to characterize rotor outlet flow in different loading configurations and to assess the resulting sampling errors. Total-pressure nonuniformity is largest in the main flow region, reaching 0.065, and is governed primarily by the transport and evolution of upstream stator wakes. Static-pressure and flow angle nonuniformities are strongest near the casing, reaching 0.055 and 4.2 deg, respectively, owing mainly to the downstream stator potential field. Increasing the number of total-pressure rakes reduces sensitivity to circumferential position, whereas increasing radial sampling improves convergence toward the area-averaged value. For the high-loading configuration, single-radial-line measurements produce maximum errors of 0.037, 0.044, 1.68 deg, and 0.037 in total pressure coefficient, static pressure coefficient, flow angle, and nondimensional axial velocity, respectively. These findings provide practical guidance for interstage instrumentation and data interpretation.