Flow Instabilities Detection in Centrifugal Blower Using Empirical Mode Decomposition

Abstract

The aim of this article is to present the application of empirical mode decomposition (EMD) for centrifugal blower flow instabilities detection. The analysis of pressure signal features extracted by EMD technique provides indicators of flow phenomena, which could be used for creating an efficient data-based controller. Quasi-dynamic pressure signals from industrial-size blower are used as an input data for EMD algorithms. An energy-based approach to intrinsic mode functions (IMF) is applied, showing the possibility of condition monitoring and instabilities detection, distinctly displaying surge conditions and inlet recirculation. Different intrinsic mode functions (IMFs) are used to detect different instabilities. EMD also presents some potential in detection of optimal operation conditions for impeller, providing additional benefit for a control system. The possibilities of EMD analysis applied to centrifugal blowers and compressors will be further investigated. INTRODUCTION Aerodynamic instabilities detection and avoidance in compressors has been a topic of interest for numerous researchers for over 75 years (Day 2015). Surge and stall are major phenomena influencing compressor performance and posing a threat to machine operation. Surge presents itself by low frequency fluid oscillations at characteristic system frequency, which is often close to the Helmholtz frequency. The structure vibration it induces are dangerous to the machine operation and can cause its destruction (Fink et al. 2008; Liskiewicz and Horodko 2015) Surge detection in centrifugal compressors is often based on previously created compressor map and locating machine operating position on it in continuous manner. The surge line is found for a particular compressor and certain margin – surge margin is created, moving the possible compressor operating point away from this line (Kurz et al. 2018). This approach, although safe and widely used, decreases compressor operating range and sometimes disallows the machine to work in the highest point of its performance curve (Fig. 1). Thus, a method allowing a compressor to safely operate close to the surge is desired. Such a goal could be attained by decreasing surge margin on compressor map, which will undoubtedly decrease safety. Other approach could be a different surge detection method, not based on a compressor map. Figure 1. Centrifugal compressor performance map (Garcia and Liśkiewicz 2016) Data-driven fault detection techniques for rotating machinery have been extensively used in many branches of industry. By means of time-series analysis, anomalies in the signal can be detected, indicating a presence of some type of