AERODYNAMICALLY INDUCED RADIAL FORCES IN A CENTRIFUGAL GAS-COMPRESSOR- PART 1 - EXPERIMENTAL-MEASUREMENT

Net radial loading arising from asymmetric pressure fields in the volu tes of centrifugal pumps during off-design operation is well known and has been studied extensively. In order to achieve a marked improvemen t in overall efficiency in centrifugal gas compressors, vaneless volut e diffusers are matched to specific impellers to yield improved perfor mance over a wide application envelope. As observed in centrifugal pum ps, nonuniform pressure distributions that develop during operation ab ove and below the design flow create static radial loads on the rotor. In order to characterize these radial forces, a novel experimental me asurement and post-processing technique is employed that yields both t he magnitude and direction of the load by measuring the shaft centerli ne focus in the tilt-pad bearings. The method is applicable to any tur bomachinery operating on fluid film radial bearings equipped with prox imity probes. The forces are found to be a maximum near surge and incr ease with higher pressures and speeds. The results are nondimensionali zed allowing the radial loading for different operating conditions to be predicted.