NASA has captured groundbreaking images of shockwaves from two supersonic aircraft, as part of its efforts to develop planes that can fly faster than the speed of sound without producing thunderous sonic boom, the US space agency said. The images were captured during the fourth phase of Air-to-Air Background Oriented Schlieren flights, or AirBOS, which took place at NASA's Armstrong Flight Research Center in the US. The flight series saw successful testing of an upgraded imaging system capable of capturing high-quality images of shockwaves, rapid pressure changes which are produced when an aircraft flies faster than the speed of sound, or supersonic, NASA said in a statement. "I am ecstatic about how these images turned out," said Physical Scientist J T Heineck of NASA's Ames Research Center.
"With this upgraded system, we have, by an order of magnitude, improved both the speed and quality of our imagery from previous research," Heineck said. Shockwaves produced by aircraft merge together as they travel through the atmosphere and are responsible for what is heard on the ground as a sonic boom. The system will be used to capture data crucial to confirming the design of the agency's X-59 Quiet SuperSonic Technology X-plane which will fly supersonic, but will produce shockwaves in such a way that, instead of a loud sonic boom, only a quiet rumble may be heard. The ability to fly supersonic without a sonic boom may one day result in lifting current restrictions on supersonic flight over land, the US space agency said. The images feature a pair of T-38s from the US Air Force Test Pilot School at Edwards Air Force Base, flying in formation at supersonic speeds.
The T-38s were flying approximately 30 feet away from each other, with the trailing aircraft flying about 10 feet lower than the leading T-38. With exceptional clarity, the flow of the shock waves from both aircraft is seen in the images, and for the first time, the interaction of the shocks can be seen in flight. "We are looking at a supersonic flow, which is why we are getting these shockwaves," said Neal Smith, a research engineer with AerospaceComputing Inc at NASA Ames' fluid mechanics laboratory. "What is interesting is, if you look at the rear T-38, you see these shocks kind of interact in a curve," he said. "This is because the trailing T-38 is flying in the wake of the leading aircraft, so the shocks are going to be shaped differently. This data is really going to help us advance our understanding of how these shocks interact," Smith said.
The study of how shockwaves interact with each other, as well as with the exhaust plume of an aircraft, has been a topic of interest among researchers. Previous, subscale schlieren research in Ames' wind tunnel, revealed distortion of the shocks, leading to further efforts to expand this research to full-scale flight testing.