Transforming Passenger Aircraft for Fuel Efficiency

Overview

The next major advance in aircraft technology may come about from the way the engine is integrated into the aircraft. The conventional commercial airliner engines we are familiar with are mounted under the wing or on the side of the rear fuselage, and great care is exercised to avoid ingesting the boundary layer—the thin layer of slower air that brushes the surface of the aircraft—into the engine to assure minimum airflow distortion.

If a distortion-tolerant fan can be developed, game-changing methods of integrating the engine into the fuselage are possible. NASA researchers, in collaboration with university and industry partners, are investigating the potential aerodynamic benefits associated with integrating the engine so that its fan ingests the boundary layer.

Project Details

To quantify the benefit of boundary layer ingestion (BLI), we are using computational fluid dynamics (CFD) to model an exciting aircraft design developed at the Massachusetts Institute of Technology (MIT), in parallel with a conventional engine configuration. Our process is as follows: The surface of the aircraft and the surrounding air is modeled using 166 million grid points with approximately 70 grids that overlap each other’s volumes; the flow of air is then solved on NASA's Pleiades supercomputer, using mathematical equations that describe and predict fluid flow; and the resulting airflow is analyzed to assess the power required to fly at cruise condition. A comparison of the resulting power requirements for each configuration measures the benefit achieved by using BLI engine integration.

Results and Impact

Our computational results show that at low speeds (70 to 120 mph), the BLI configuration has a substantial benefit over a conventional configuration. If this benefit can be shown to exist at higher speeds, and distortion-tolerant fans become a reality, then future aircraft may be able to fly using 60% less fuel for each flight compared to current aircraft—resulting in substantial savings for all airline operators. It would also result in lower flight costs for airlines, possibly translating to lower ticket prices for passengers. The computational results also show the reason for the benefit: the kinetic energy associated with the fuselage boundary layer, which would be lost on a traditional configuration, makes fan operation more efficient for the BLI configuration.

Why HPC Matters

Accurate CFD simulations require a large number of grid points to capture the physics of the airflow along the aircraft surface and the surrounding air. For example, a grid for just half of the BLI configuration consists of approximately 166 million grid points, which requires an enormous amount of computational power to solve. A single computational run at a single flight condition and one engine power setting requires approximately 25,000 processor-hours on the Pleiades supercomputer at the NASA Advanced Supercomputing (NAS) facility. Our geographically dispersed team, working on both coasts of the United States, also takes advantage of NAS's ultra-fast networks for efficient collaboration.

What's Next

The benefit of the BLI engine integration must now be shown to exist at real-world commercial aircraft speeds. Our next step is to redesign the aircraft so that it is efficient at higher speeds, and then assess the BLI benefit at Mach 0.7 to Mach 0.85 to do trade studies of fuel efficiency versus speed.

More Media

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