Stall and Surge in Wet Compression: Test Rig Development and Experimental Results

Wet compression is a strategy adopted to increase the power output of gas turbines, with respect to dry conditions, usually also incrementing the operating range of the compressor. However, stall and surge are two aerodynamic instabilities which depend on many factors, and they are expected to occur even in wet compression at low flow rates. Despite the many studies carried out in the last 80 years, literature does not offer many works concerning these instability phenomena in wet compression. In this paper, an experimental analysis of stall and surge in wet compression conditions is carried out on an axial-centrifugal compressor installed in an existing test rig at the Engineering Department of the University of Ferrara. The intake duct was implemented with a water injection system (WIS) which allows the uniform mixing of air and water before the compressor inlet. The control and data acquisition system of the test bench was updated with new hardware and software to obtain faster data sampling. Transient and steady-state tests were carried out to make a comparison with the experimental results in dry conditions. The analysis was carried out using traditional thermodynamic sensors, by means of both classic postprocessing techniques and cyclostationary analysis. The aim is to (i) evaluate the influence of wet compression on the stable performance of the compressor, (ii) qualitatively identify the characteristics of stall and surge in wet compression, and (iii) demonstrate the reliability of cyclostationary analysis in wet compression conditions for stall and surge analysis.