Considerations for the Use of Variable Geometry in Gas Turbines

Abstract

The loss of performance of a gas turbine at off-design is primarily due to the rapid drop of the major cycle performance variables with decrease in output, and this may be aggravated by poor component performance. Postulated propulsion demands require that future engines attain performances much more advanced than those of the present day. The specific nature of the improvement in performance will depend on engine duty, but it is expected that the improvement will include higher power loadings and better response, in addition to better fuel burn characteristics. Innovative design and advanced materials and structures will play key roles in bringing about a revolution in gas turbine technology, but these will have to be accompanied by novel control methods which can influence the position of the engine operating point. The latter may require the use of variable geometry in one or more gas path components to improve the internal matching of a component or to re-match the engine cycle such that the component operating point and/or the primary cycle performance variables are re-optimized or controlled with changing operating conditions. This paper examines how variable geometry could be used to improve the off-design performance of gas turbines.