Physics-Based Aeroanalysis Methods for Open Rotor Conceptual Design

Operating costs and fossil fuel consumption of civil transports can be reduced through use of efficient counter rotating open rotor (CROR) propulsion systems, thereby addressing both key industry needs and long-term NASA technical goals. To develop such next-generation systems, multiple design variables must be assessed efficiently within a conceptual design software environment. A blend of physics-based, mid-fidelity tools featuring low CPU and ease of setup can provide this capability. Phase I built on an established, highly efficient lifting surface free wake model, the CDI CHARM analysis, and also began initial development of a novel variant of the CDI Cartesian Grid Euler (CGE) model to yield fast-turnaround, low- mid fidelity tools well suited to this requirement. Phase I involved several key upgrades to CHARM and preliminary validation on representative CROR designs. Regarding CGE, formulation of the new rotating frame and multirotor capability has been largely completed, and demonstrations of single rotor modeling are complete. Phase II will entail: additional upgrades to the CHARM rotor blade and airfoil models for improved fidelity; completion of implementation of the CGE analysis for CROR cases; integration of the two models into a unified CHARM-CGE AeroAnalysis (C2A2) architecture; and extensive validation and operational testing.

Open rotor propulsion systems can help meet long range emission reduction targets in support of initiatives such Green Aviation. The final Phase II C2A2 code package will be made available to NASA engineers, and will aid multiple investigations of the potential of advanced CROR propulsion concepts to improve fuel efficiency and reduce the environmental footprint of commercial transports. In addition, to direct analysis of particular CROR designs, the model can efficiently produce full performance maps of candidate designs for use in conjunction with system-level design studies. The C2A2 software can also enhance analysis and conceptual design capabilities for assessment of novel air vehicles featuring Integrated and Distributed Propulsion systems such as the ongoing LeapTech initiative. Finally, the modeling capabilities of the CHARM and CGE codes can be exploited- in conjunction with standard noise models - to support initial studies of unsteady loading and acoustics for these advanced concepts.

The enhanced fast-turnaround, physics-based analysis and design tools for CROR systems that will emerge from Phase II will support both civil aircraft manufacturers and DoD. The US Air Force is actively seeking more efficient future transports, and airframers and private industry can utilize these tools in designing aircraft with lower emissions footprint and a superior balance of reduced fuel burn in cruise and community noise impact. Spinoffs of the model to the design of propulsion systems for compound rotorcraft and UAVs are also possible. Phase III commercialization will benefit from the beta testing that will be a feature of the Phase II, as well as by offering new capabilities the pre-existing installed base of CHARM and CGE software users.

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