Variable Speed Turbine Technology Development and Demonstration

The objective of this technical report is to provide a summary of the research performed under the NASA Revolutionary Vertical Lift (RVLT) Project to develop and demonstrate required engine technologies and designs for achieving a 50% reduction in rotor rotational speed via engine speed changes alone with a fixed ratio drive system while maintaining high engine efficiency over the wide operational speed range. This research culminated in a joint effort between the ARMY and NASA to develop and demonstrate a Variable Speed Power Turbine (VSPT) with an efficiency of 1) 92% or better at the Maximum Rated Power (MRP) condition corresponding to operation at sea-level conditions to hover at 100% rotational speed and 2) Efficiency of 90% or better at the Maximum Continuous Power (MCP) corresponding to cruise at 25000ft at Mach 0.5 at 55% rotational speed. NASA VSPT blade cascade testing at high and low inlet turbulence levels over a large range of Mach numbers, Reynolds numbers, and incidence provided a benchmark data base to validate the ability of CFD analysis codes to predict the VSPT losses over the entire flight operating envelope. These test results were also used to validate the ability of models to predict flow separation and laminar-to-turbulent flow transition. To demonstrate the VSPT technology, a notional engine was developed and the power turbine was designed to meet the NASA/Army performance requirements under the Army's Advanced Variable Speed Power Turbine (AVSPOT) program. Based on the notional engine a VSPT component test rig was designed, fabricated, and tested to demonstrate that their design would meet the performance requirements. The tested VSPT exceeded the efficiency goals of the design. Furthermore, the lapse between the MCP and MRP conditions was closely matched by CFD predictions, providing confidence in using these predictive tools in future applications. The technology development work completed on this contract is expected to transition to a viable engine demonstration in the future.