A helicopter gas turbine requires an overall compressor pressure ratio of 10:1. This is to be obtained using a two-spool layout consisting of a four-stage Z02 Gas Turbine Theory 93093.indd 578 27/04/2017 07:21 APPENDIX B PROBLEMS 579 axial compressor followed by a single-stage centrifugal compressor. The polytropic efficiency of the axial compressor is 92 per cent and that of the centrifugal is 83 per cent. The axial compressor has a stage temperature rise of 30 K, using a 50 per cent reaction design with a stator outlet angle of 208. If the mean diameter of each stage is 25.0 cm and each stage is identical, calculate the required rotational speed. Assume a work-done factor of 0.86 and a constant axial velocity of 150 m/s. Assuming an axial velocity at the eye of the impeller, an impeller tip diameter of 33.0 cm, a slip factor of 0.90 and a power input factor of 1.04, calculate the rotational speed required for the centrifugal compressor. Ambient conditions are 1.01 bar and 288 K. [Axial compressor 318 rev/s, centrifugal compressor 454 rev/s]