Experimental And Numerical Study Of Centrifugal Compressor Stability Enhancement

Combined heat and power system based on small gas turbine is one of the most potential developing direction of distributed energy system, because of its environmental friendliness, high reliability for power supply and good adaptability to varied heat and electricity. Stable working range of the centrifugal compressor used in small gas turbine need to be extended due to steam injection. This paper did the experimental study and numerical simulation of centrifugal compressor stability extension.Aiming at extending the compressor operating range by8%, this paper did a systematic research about compressor with vaned and vaneless diffuser with two extension measures, bleeding at impeller throat and injecting at diffuser inlet.In the experimental part, two parts were included. For the centrifugal compressor with vaned diffuser, with bleeding at impeller throat, the SMI (Surge Margin Improvement) was4.32%and3.18%at80%,90%design speed, respectively. Injecting steam at the diffuser inlet, where8equispaced injectors set at the shroud side, took different effects on the compressor based on the speed. For the centrifugal compressor with vaneless diffuser, with bleeding at impeller throat, the SMI was-0.55%at80%design speed, and2.24%at90%design speed. Injecting steam at the diffuser inlet, where4injectors set unequally at the shroud side, could make the compressor surge happen earlier unser90%design speed, and the larger the injecting mass flow, the earlier the surge happened.In order to further study the cause of centrifugal compressor instability, the three-dimensional viscous steady CFD simulation on compressor with vaneless diffuser under90%design speed was made. Based on validation, the calculation results showed that bleeding at the impeller throat can augment the impeller relative velocity diffusion ratio and decrease the tip blade loading, thus improving the flow condition of the compressor and extend its stable operation range. While injecting steam at the diffuser inlet in this simulation, extension effects which increased as the injecting mass flow increased at some degree, got the best result when the steam injection mass flow was4g/s. But when steam injection mass flow was as large as lOg/s, the compressor surge happened earlier. That because the wall attachment effect was destroyed, and core flow condition in the vaneless diffuser was affected, causing the vaneless diffuser surge.