Axial Compressor Reversed Flow Performance.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The results of an analytical study of compression system forced response and an experimental investigation of the reversed flow performance of a three-stage axial-flow compressor are presented. A one dimensional lumped parameter description of the dynamics of a simple compression system was found to be capable of simulating the circumstances under which the imposition of a periodic external excitation can force a normally surging compression system into a small amplitude oscillation about the nonrecoverable stall point. This forces oscillation can then decay into a system stagnation upon termination of the external excitation. It was also found, however, that predictions of compression system forced response behavior were heavily dependent upon the model used for defining compressor post-stall performance, both steady state and transient, especially in the reverse flow and mass flow and shutoff operating regimes. The complete set of pressure rise and torque characteristics of a three-stage axial-flow compressor are presented. Two stable stalled flow modes have been observed in the multi-stage axial compressor builds tested 1 rotating stall, and 2 full annulus stalled flow. The transition to each of the two stalled modes is accompanied by a discontinuous drop in overall time-averaged pressure rise and torque performance. Although a large hysteresis is associated with the unstall-rotating stall transition which occurs at a relatively large positive flow coefficient, the transition from rotating stall to the annulus stall mode which occurs at a negative flow coefficient near shutoff has no hysteresis.
- Hydraulic and Pneumatic Equipment
- Fluid Mechanics