Aerodynamic and Geometric Design Criteria for the Performance of Low Powered Vehicular Gas Turbines

A study of the design criteria for the performance of small single and two-spool vehicular gas turbines using metallic rotors shows that the acceleration capability, i.e., component inertia and the net power output, determine to a large degree the obtainable cycle efficiency. Fluid viscosity effects and manufacturing limitations cause the cycle efficiency to decrease with decreasing net powers. When fast acceleration capability is desired, aero-dynamically compromised component designs may have to be selected which causes an efficiency penalty. It is found that the blade height of the compressor turbine in two-spool designs is a significant parameter for this penalty. One interesting result of the calculations is that single spool designs using metallic radial inflow turbine rotors can be quite competitive with two-spool designs using ceramic rotors in regard to efficiency. They suffer, however, from a comparatively high rotor inertia, i.e., reduced acceleration capability. Areas of uncertainties remain for the loss relations so that the calculated performance values must be viewed as trend data. The prime performance parameter used in this study is the flow path efficiency. The thermal cycle efficiency is presented only for constant values of heat exchanger effectiveness and mechanical efficiency.