September 13, 2013
NASA Focuses On Supersonic Shockwaves
Brett Smith for redOrbit.com – Your Universe Online
New images released by NASA depict actual shockwaves in vivid colors emanating from a plane flying at supersonic speed.
Using a twin telescope and digital camera system on the ground at NASA’s Dryden Flight Research Center, scientists created schlieren images, which show density variations in air and other transparent media. Special illumination in the images mark changes in the density of the air, revealing the shockwaves.
"Our team was able to photograph truly spectacular images showing the shockwaves of full-scale supersonic aircraft in flight,” said Ed Haering, principal investigator of Dryden’s new Ground-to-Air Schlieren Photography System (GASPS).
“For new quiet supersonic aircraft designs, computer simulations and wind tunnel tests are used to model how to minimize the loudness of the sonic booms, but the simulations and wind tunnel tests have challenges in accurately modeling the flow around engine inlet and tail regions,” Haering explained.
"We can use these images to validate our computer simulations and wind tunnel tests, giving us confidence that we can properly design supersonic civil aircraft of the future,” he added. “Then we will be able to fly over land at about double the speed of current civil aircraft without bothering people on the ground.”
Previous schlieren photography has used an elaborate series of lenses and other devices to capture supersonic shockwaves on film and has shown them as contrasting streaks against a stark background like the edge of the sun. In contrast, the GASPS project uses just a telescope and a digital camera, meaning the heavy lifting associated with creating the images is performed post-flight using computer software. The NASA scientists said this improved method greatly reduces the precision needed.
Schlieren imaging gives the location and relative force of supersonic shockwaves in clear and stark terms. The new method represents another tool used by NASA researchers to characterize sonic booms.
GASPS represents the latest project in a long history of sonic boom research by NASA. The space agency is said to currently be working on reducing sonic boom impact – potentially leading to supersonic flight taking place over the US.
In another project described earlier this year, NASA has created a living room-like space to test the effects of a sonic boom on a domestic environment. Acoustics experts at NASA said they wanted to gauge people’s perceptions of noise. They found that some noises are more annoying to people than others.
"That includes loud or startling things that make you have this sort of fear reaction - you think there's danger because there's a really loud sound," said NASA engineer Alexandra Loubeau. "Most people are most annoyed by those sounds."
During one of the test sessions, NASA researchers invited 33 people from the local community to sit in the Interior Effects Room and listen to boom and rattle sounds designed to model those caused by a plane cruising at supersonic speeds.
“The point of the test is for us to develop a capability to predict the annoyance caused by these sounds in the population," said NASA aerospace engineer Jonathan Rathsam. "Right now supersonic flight is forbidden over land because conventional booms are annoying to communities on the ground.”
“This predictive model will be used by aircraft designers to determine how much a particular design is likely to annoy listeners on the ground and aircraft noise regulators to develop a metric to regulate what might be an acceptable level for sonic boom,” he added.