Effects of Pressure Ratios of Axial Flow Compressors on the Deep Surge Frequencies : Part I : Effective Reduced Surge Frequency and Its Behaviors

Effects of compressor pressure ratios and flowpath geometries on the frequencies of deep-surges in multi-stage axial flow compressors are studied on the basis of numerical experiments. The frequencies tend generally to lower in a complicated manner toward higher rpms and higher pressure ratios of the compressors. The general behaviors of the frequencies are found to be described in large in terms of an effective reduced surge frequency numerical-experimentally searched for. The parameter tends to keep a nearly constant level of values for a wide range of stalling pressure ratios, rpms, and number of stages of compressors. For multi-stage compressors, however, at slightly below the design speed, the parameter values tend to drop rather steeply, and above the speed, they tend to keep again a new constant level of values at the lowered level. The transition of the behavior is more significant for the conditions of compressors designed for higher pressure ratios and in shorter delivery flow-paths. It could be attributed to the effect of a relocation of surge-triggering stages in the local zone of the surge flow mode with the amplitude varying much in the axial direction. The detailed phenomena involved in the behaviors will be clarified in Part 2.