Abstract
Aerodynamic instabilities in centrifugal compressors are dangerous phenomena affecting machine efficiency and in severe cases leading to failure of the compressing system. Quick and robust instability detection during compressor operation is a challenge of utmost importance from an economical and safety point of view. Rapid indication of instabilities can be obtained using a pressure signal from the compressor. Detection of aerodynamic instabilities using pressure signal results in specific challenges, as the signal is often highly contaminated with noise, which can influence the performance of detection methods. The aim of this study is to investigate and compare the performance of two non-linear signal processing methods—Empirical Mode Decomposition (EMD) and Singular Spectrum Analysis (SSA)—for aerodynamic instability detection. Two instabilities of different character, local—inlet recirculation and global—surge, are considered. The comparison focuses on the robustness, sensitivity and pace of detection—crucial parameters for a successful detection method. It is shown that both EMD and SSA perform similarly for the analysed machine, despite different underlying principles of the methods. Both EMD and SSA have great potential for instabilities detection, but tuning of their parameters is important for robust detection.
Highlights
Centrifugal compressors are machines of great importance for a wide range industries, operating in petrol engines, turboshaft engines and industrial plants of various kinds [1].The compressor operating range is limited by choke for high mass flow rates and the appearance of aerodynamic instabilities at low mass flow rates [2]
Empirical Mode Decomposition (EMD), each subsequent intrinsic mode functions (IMFs) is of lower frequency, while for Singular Spectrum Analysis (SSA), the Reconstructed Components (RCs) do not have to be ordered by the frequency
Based on energy of selected components, the overall detection possibilities and signal length needed for robust identification of inlet recirculation and surge were compared
Summary
Centrifugal compressors are machines of great importance for a wide range industries, operating in petrol engines, turboshaft engines and industrial plants of various kinds [1]. The compressor operating range is limited by choke for high mass flow rates and the appearance of aerodynamic instabilities at low mass flow rates [2]. The compressor peak efficiency region is adjacent to the unstable region, it is not uncommon for instabilities to appear during standard machine operation, when a slight change in external conditions takes place. There exist a number of well-described instabilities, such as inlet recirculation, rotating stall or surge [3,4]. The instabilities in centrifugal compressor may vary in effect, ranging from drop in efficiency for inlet recirculation [6], through non-synchronous vibrations introduced by rotating stall [7], up to an abrupt destruction of a compressor in case of surge [3]
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