Stall and surge in wet compression: Test rig development and experimental results

Wet compression is a strategy adopted to increase the poweroutput of gas turbines, with respect to dry conditions, usuallyalso incrementing the operating range of the compressor.However, stall and surge are two aerodynamic instabilities whichdepend on many factors, and they are expected to occur even inwet compression at low flow rates. Despite the many studiescarried out in the last 80 years, literature does not offer manyworks concerning these instability phenomena in wetcompression. In this paper, an experimental analysis of stall andsurge in wet compression conditions is carried out on an axialcentrifugal compressor installed in an existing test rig at theEngineering Department of the University of Ferrara. Somemodifications of the test rig were necessary.The intake duct was implemented with a water injectionsystem which, by means of water spray injectors, allows theuniform mixing of air and water before the compressor inlet. Thecontrol and data acquisition system of the test bench was updatedwith new hardware and software to obtain faster data sampling.Transient and steady-state tests were carried out to make acomparison with the experimental results in dry conditions. Theanalysis was carried out using traditional thermodynamicsensors, by means of both classic post-processing techniques,and cyclostationary analysis.The aim is to i) evaluate the influence of wet compressionon the stable performance of the compressor ii) qualitativelyidentify the characteristics of stall and surge in wet compressionby means of sensors which were shown to capture thesephenomena well and iii) demonstrate the reliability ofcyclostationary analysis in wet compression conditions for stalland surge analysis.