Numerical study on the performance of centrifugal compressor in the combined Diesel-Brayton cycle engine

The combined Diesel-Brayton cycle engine which combines gas turbine and diesel engine has high power density and good startability under the low temperature conditions. And the fuel consumption is reduced under subpower conditions by switching operating mode. High pressure air after compressor needs to be taken out for diesel engine. The influence of large-mass-flow bleed to the performance of the centrifugal compressor was studied. The present paper is the fundamental for designing the combined Diesel-Brayton cycle engine. The performance and three-dimension flow field of the centrifugal compressor were investigated by simulation in the present paper. The simulation was carried out by NUMECA Fine Turbo. Each passage had one suction hole between two vaned diffusers. Two ways of releasing compressed air were designed, and suction holes in both schemes were squares. Holes in scheme A were at upstream of diffuser blades and holes in scheme B were at upstream of passage. The numerical results show that pressure ratio decreases 1.66% in scheme A and 1.49% in scheme B when bleeding 10% air. And the efficiency of the compressor decreases about 1% in both schemes. The range of mass flow is almost the same.