The analysis of compression system instabilities using approximate entropy for centrifugal blower

This paper examines the early-stage nonlinear disturbances that preceded deep surge in a centrifugal compressor and proposes the use of Approximate Entropy (ApEn) as a diagnostic indicator in a novel combination with its derivative (DApEn). ApEn, a statistical measure of time-series irregularity, is applied to pressure signals acquired from multiple locations within the system. Results reveal that as the flow becomes increasingly unstable, the regularity of the pressure signal deteriorates, resulting in elevated ApEn values. Moreover, the emergence of sharp variations in differential Approximate Entropy (DApEn) serves as a sensitive marker for the onset of flow instabilities, including inlet recirculation and surge. The findings, obtained on a low-speed centrifugal compressor, demonstrate the method’s ability to capture subtle changes in system dynamics and indicate its potential for wider turbomachinery applications that will require future validation.