Reverse-Flow Turboshaft Engine Study

Abstract

Abstract : The report presents the results of a program conducted to investigate the characteristics of a three-spool turboshaft engine having an unconventional turbine arrangement. In this engine, called a three-spool reverse-flow turboshaft engine, the combusted air passes through the high pressure (HP) turbine, then the power turbine, and finally through the low-pressure (LP) turbine. The performance, weight, envelope, and transient characteristics of this engine were compared to those of a more conventional two-spool turboshaft engine of comparable life and component technology. In addition, the suitability of the three-spool reverse-flow turboshaft engine for recuperation was assessed. The results of the study indicated that the three-spool reverse-flow turboshaft engine provides better part-power specific fuel consumption (SFC) than the two-spool engine. However, te engine is sensitive to ambient temperature variations, necessitating flat-rating of the engine to minimize the hot-day power lapse; is somewhat heavier; has a slightly larger envelope (length and diameter) and higher power-output speed; and requires approximately 3 seconds longer to accelerate from flight idle to 95 percent MRP. The reverse-flow engine component arrangement appears to have its greatest potential in a recuperated configuration.