A Computational Tool for High Advance Ratio Configurations

Newer vertical lift configurations consider speed as an important design parameter with forward speeds upwards of 230 Knots, which is well above the acceptable incompressible flow regime. In such high speed vertical lift configurations, even though the aircraft may be cruising at compressible Mach numbers, incompressible flow pockets can occur in the wake of the fuselage. Hence, in contrast to most helicopters currently in use, these configurations need to be analyzed across a wide range of speed regimes including incompressible, compressible and mixed regimes. The present proposal offers to extend the design tool ``RotCFD'' to viscous all-speeds with mixed incompressible and compressible regions. In general, the algorithms used in CFD are designed for incompressible flow or compressible flow, depending upon the primary usage. RotCFD, being an Integrated Design Environment (IDE) for rotors, can be developed to seamlessly work in both regimes without additional input besides the operating speed from the design community. Additionally, this proposal offers to extend RotCFD to include grid generation with bodies in relative motion, such as tilting nacelles and wing tips, which happens in transitioning flight. The proposed extension of RotCFD for all-speed regimes and flows with mixed regimes, if proven successful, will offer the vertical flight scientific community a moderate fidelity, robust and efficient design tool. With the added potential to simulate relative motion of components, the tool will provide an analysis capability for all operational regimes: hover, conversion and cruise.

NASA's interest in civil rotorcraft research such as LCTR2 prompts for a computational tool which can analyze compressible and mixed regime flows in an easy to learn and robust Integrated Design Environment. The proposed design tool accomplishes this goal, especially in the areas where transitioning flight and moving bodies such as nacelles and winglets are required.

RotCFD with mixed speed flow regimes and moving bodies will be an asset to any organization with a need to analyze a high-speed rotorcraft design or develop a new design. The tool will be useful to other government agencies including the Army, Navy and Air Force. In the rotorcraft industry, the proposed tool can be used to assist the design process.

This is a mature technology (TRL 7) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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