Off-design performance of various gas-turbine cycle and shaft configurations

The design-point performance of various gas turbine cycles such as simple, regenerative, and intercooled-regenerative, is well understood. It is also understood that more elaborate shaft arrangements such as one, two, or thre e concentric or nonconcentric shafts, and a separate power turbine shaft, p rovide better starting and operational flexibility, and wider plateaus of h igh off-design performance. However, the types of different off-design perf ormance one can obtain with these different shaft arrangements has not been previously reported. In this paper we use a computer program to investigat e the design-point and off-design-point performance of engines with the fol lowing: one single shaft joining the compressor, turbine and load; one shaf t joining compressor and turbine, and one shaft for the power turbine; two shafts for compressor and turbine, and one shaft for the power turbine; and three shafts joining the compressor and turbine, and one shaft for the pow er turbine. This is done by specifying typical compressor and turbine maps, and computing various aspects of off-design performance. The advantages an d disadvantages of the various arrangements are investigated and discussed.