CFD Support for Quiet Supersonic Aircraft Design

Overview

NASA is investigating innovative ways to improve aircraft design to allow for supersonic flight over land. Currently, the Federal Aviation Administration (FAA) bans civilian supersonic flights over the United States and its territorial waters due to the loud sonic booms that aircraft generate when flying above the speed of sound. To address this issue, NASA researchers are working on developing technologies to enable quiet supersonic aircraft designs. The new designs feature detailed shaping of the entire aircraft to reduce or mitigate shocks and prevent shocks from merging together as they propagate through the atmosphere and reach the ground.

Project Details

Several NASA research centers—Ames, Langley, Glenn, and Armstrong—have partnered with industry to develop a Low Boom Flight Demonstrator (LBFD) in order to validate the low-sonic-boom characteristics of modern civilian aircraft designs that NASA and industry have been studying for nearly a decade. The LBFD is planned as one of several experimental NASA X-planes. In order to be cost-effective, it will use parts from existing fighter aircraft, and will therefore be the size of a small business jet. The LBFD will perform a series of flight tests, during which detailed ground pressure signatures (loudness) will be measured. These signatures will then be compared with results from computational fluid dynamics (CFD) solvers to assess the capabilities of computational methods to predict sonic boom.

Significant advances in CFD simulations have given NASA and industry confidence to accurately predict the pressure signature of aircraft designs. In this project, CFD simulations were performed using NASA's Launch, Ascent, and Vehicle Aerodynamics (LAVA) solver. To examine the noise level that would be produced by a given LBFD design, pressure signature data from 1-5 body lengths away from the vehicle is extracted from the CFD results, then the signature is propagated through the atmosphere.

Results and Impact

The computational results enable the LBFD designers to assess the sonic boom and vehicle performance prior to a flight test, and to address any part of the aircraft's design where changes are required to decrease its sonic boom pressure signature on the ground. Ensuring that the design has the required pressure signature is critical because the X-plane must meet extremely stringent sonic boom loudness levels to convince the FAA to allow civilian supersonic flight vehicles in the future. The demonstrator vehicle will perform various tests, including community flyovers, to evaluate the validity of a quiet supersonic design. The results of these tests will help inform the designs of future supersonic aircraft designs, as well as provide data to support an FAA review of the current ban on supersonic flight.

Why HPC Matters

CFD simulations of the X-plane in flight require accurate modeling of both the aircraft and the flow field that occurs in its vicinity. This is accomplished by generating a computational model of the full aircraft and its nearby airspace; typically, this model requires 50 to 100 million grid cells. For a model of this size, a single computational run requires approximately 750 processor-hours on the Pleiades supercomputer at the NASA Advanced Supercomputing facility at Ames. By assuming symmetry in our simulations, we are able to halve the computing requirements for each simulation by computing the flow over only half of the airplane.

The pressure signatures of each design studied are extracted from the simulations obtained at Ames and provided to researchers at Langley, who use this data to determine the sonic boom loudness level on the ground. NASA's high-speed network allows the team members from the various centers and industry partners to transmit data efficiently, as well as helping to coordinate efforts.