Supercomputers Help Aircraft Noise Reduction Technologies Come in for a Landing
Those of us who live in communities near large airports have countless opportunities to notice how loud airplanes can be during approach and landing. Surprisingly, the roar of the engines is not the primary source of the noise we hear: turbulent airflow around the plane’s body, known as the airframe, generates much of the sound.
In June, NASA announced that successful flight tests had demonstrated new technologies that could reduce airframe noise by more than 70%—without impacting aerodynamic performance. The noise abatement methods were developed after years of research by aeronautics experts at the agency, including simulations that require millions of processor hours on the Pleiades supercomputer at the NASA Advanced Supercomputing (NAS) facility, located at Ames Research Center.
Research Leads to Innovative Designs
To determine where the most turbulent airflows occur and how their interactions increase the overall noise levels, aerospace scientist Mehdi Khorrami and his team at NASA’s Langley Research Center have simulated landing configurations of several types of aircraft on Pleiades over the years, including a Gulfstream research model and the Boeing 777 airliner. Using physics-based, highly complex modeling and simulation methods, the researchers identified three key parts of the airframe where noise reduction efforts would likely have significant impact: the landing gear, wing flaps, and cavities in the airplane’s body that remain open when the landing gear is deployed.
“Because these systems are so intricate, they are very difficult to simulate,” said Khorrami, principal investigator of NASA’s Acoustic Research Measurement (ARM) project. “In addition to the complex geometry, we have to accommodate vastly different spatial and temporal scales. Pleiades, along with advances in computational methodologies, enable us to develop and run models and simulations whose complexity we could only envision a decade ago.”
The extensive simulations produced by Khorrami’s team helped aerospace engineers develop practical, efficient noise reduction concepts that were evaluated during the recent ARM flight test campaign, which was carried out at NASA’s Armstrong Flight Research Center in California.
New Simulations Support Flight Test Campaign
To support the flight tests, the researchers ran full-scale simulations using a high-fidelity CAD model that was created by laser-scanning the entire surface of the SubsoniC Research Aircraft Testbed (SCRAT)—NASA’s Gulfstream III (G-III) research aircraft—and its individual components. “Working closely with the flight test team, we predicted results ahead of the flights, and directly compared our simulation results with test measurements to validate the accuracy of the predictions,” Khorrami said.
The noise abatement concepts used in the flight tests included placing various porous and non-porous fairings around the landing gear to allow a portion of the airflow to move through the gear, reducing the turbulent flow that leads to noise. Originally developed for aeroacoustic testing on a larger G-V aircraft, the fairings went through several significant design changes prior to the G-III test flight. Khorrami and his team evaluated the aeroacoustic performance of each design change by simulating the full-scale aircraft with landing gear deployed and fairings installed. With each iteration, they provided results of their analysis to the design engineers, further optimizing the configuration. The final design provides maximum noise reduction without impacting aerodynamic performance.
Simulations further contributed to the success of the flight tests by helping to evaluate the aeroacoustic performance of another technology—a flexible wing called the Adaptive Compliant Trailing Edge (ACTE), which uses a stretchable material to eliminate gaps/tips that generate noise when wing flaps are deployed during landing.
Run on Pleiades using Exa Corporation's PowerFLOW code, the high-fidelity simulations required computational grids comprising billions of cells and produced hundreds of terabytes of data. NAS visualization experts helped Khorrami’s team visualize the results of these massive datasets by developing detailed, informative images and animations like the one shown above.
With the success of the ARM flight tests, design engineers can now begin work to determine how the new technologies could be added to existing aircraft, where feasible, and incorporate them into future aircraft designs.
—Michelle Moyer, NASA Ames Research Center
