Investigation on probe streamwise distribution for surge measurement in compression system

Abstract

Compressor surge is a typical unstable phenomenon generally resulting in violent aerodynamic oscillation in a compression system. Because of the hysteresis caused by the unsteady flow behaviors during the surge cycle in a compression system, some aerodynamic properties show clear distinctions with altered streamwise positions. In order to obtain the transient surge characteristics accurately in the experiment, the probes should be reasonably positioned along the streamwise positions. In this paper, a one-dimensional-three-dimensional (1D-3D) coupled method is used to study the streamwise variance of aerodynamic properties during the surge process in the compression system including a centrifugal compressor and downstream pipe system. The results show that for the mass flow rate, the surge amplitude decreases gradually along the downstream pipe. In contrast, the amplitude of the mid-frequency mass flow fluctuation caused by pressure wave propagation increases firstly and then decreases. For unsteady pressure characteristics, the amplitude of pressure oscillation during the surge cycle along the downstream pipe system is almost the same. For temperature characteristics, when the surge occurs, the strength of reverse flow increases dramatically, which makes the temperature increment near the casing wall at the compressor inlet come up to 60.6% of the temperature before surge inception, also the temperature increment is faster than the pressure response at compressor outlet. The variance analysis concerning aerodynamic properties along the streamwise direction of a compression system can provide the following guidance for engineering practice of surge test or monitoring: the transient mass flow probe should be placed close to the compressor outlet in order to obtain the dynamic mass flow characteristics more accurately, and the distance between pressure sensors and compressor outlet has little influence on the accuracy of dynamic pressure measurement in a surge cycle. Moreover, the surge inception can be judged accurately and quickly by placing high-frequency temperature sensors on the casing at the compressor inlet.