Effect of Air Recirculation on Compressor Performance (Dept.M)

Abstract

Rotating stall and surge are two aerodynamic instabilities in compressors. The instabilities limit the flow range in which the compressor can operate "surge margin". Surge and rotating stall also restrict the performance (pressure rise) and efficiency of the compressor. Compression system modeling is very important because development a suitable control system requires a deep understanding of the transient behavior of the compressor to be controlled. The model of compression system is used for capturing the dynamics of rotating stall and surge. Recirculation technique is used to eliminate the instabilities of compression system, where bled air from downstream compressor via bleed valves re-circulates to injectors at compressor inlet. The form of the modeling takes the four-state low order model which applied to design the nonlinear controller.. By using recirculation technique the compressor works in stable-regime. At the rotor speed ratio (N/Ndesign) of 100% and recirculation flow approximately of 11% the gain is 13%. At ratio from (60-80) % with recirculation flow approximately (7-9) % the gain in the range (22-25%). The higher gain becomes 40% at rotor speed ratio approximately 90% at recirculation flow approximately 8%.