Regression Analysis of Centrifugal Compressor Characteristics in the Entire Operating Range for Non-Linear Mathematical Model

Abstract

Centrifugal compressors are widespread in gas turbines – for example in thrust or turboshaft engines in the field of aviation, or in power generation. The main features of centrifugal compressors are high pressure ratio per each stage and stable operation at a relatively wide range of the fluid flow. Despite these advantages at low mass flow rates, some kind of instabilities appear (like rotating stall and surge), which are the same in axial compressors and which may occur in the form of total pressure and mass flow rate fluctuation. It is very important to avoid these instabilities to protect the equipment and the connected systems, because the energy stored in the fluctuations is enough for the disintegration of impeller blades as well. Creating a mathematical model of the centrifugal compressor is very important regarding the prediction of the system behavior in different operational modes, and in the unstable operational ranges an active surge suppression system could avert the undesired  regimes which could occur in the lack of any active surge avoidance system. The objective of our paper is to describe the mass flow rate – pressure ratio and mass flow rate – efficiency characteristic of the equipment by polynomial regression approximation method based on the result of earlier measurement. The equation created by this method covers the whole operational range, its advantages are shown by a comparison method instead of the result of earlier linear methods (for example bilinear equation by relative physical revolution and dimensionless mass flow rate). The mathematical model of the compressor was tested by dynamic simulations in MATLAB Simulink environment, and the solution was validated by the result of transient measurements. The created dynamic model opens the way to the development process of a state-of-the-art, active surge suppression control system.