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NASA researchers in California are using a modern version of a year-old German photography technique to capture images of shock waves created by supersonic airplanes. The results will help engineers to design a quiet supersonic transport. Although current regulations prohibit unrestricted overland supersonic flight in the United States, a clear understanding of the location and relative strength of shock waves is essential for designing future high-speed commercial aircraft.
Schlieren imaging reveals shock waves due to Free Schlieren news density gradient and the accompanying change in refractive index.
This Unterstrass escorts girl requires the newss of fairly complex optics and a bright light source, and until recently most of the available schlieren imagery of airplanes was obtained from scale model testing in wind tunnels.
Acquiring schlieren images of an aircraft in flight is much more challenging. Ground-based systems, using the sun as a light source, have produced good results but because of the distances involved did not have the desired spatial resolution to resolve small-scale shock structures near the aircraft. More recently, synthetic schlieren techniques have been developed based on image processing methods.
One, called background oriented schlieren BOShas been particularly successful in wind tunnel tests. First, researchers obtain an image of a speckled background pattern. Next, they collect a series of images of an object in Schlieen flow in front of the same pattern.
Shock waves are deduced from distortions of the background pattern resulting from the change in refractive index due to density gradients. This method requires very simple optics and Free Schlieren news variety of background patterns, including natural ones, may be used. The complexity with this method is in the image processing and not the hardware or positioning, thus making BOS an attractive candidate for obtaining high-spatial-resolution imaging of shock waves in flight. Allschwil speed dating high-speed camera on the underside of a NASA Beechcraft B King Air captured frames per second while the supersonic target aircraft passed several thousand Free Schlieren news underneath in straight-and-level flight at speeds up to Mach 1.
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Researchers acquired imagery with a relatively simple system consisting of a laptop with a frame grabber and using natural desert vegetation as the speckled background pattern, a method the team dubbed "Tumbleweed Tech. Heineck, the NASA Ames principal investigator who originally proposed the idea of using the background oriented air-to-air technique. Ed Schairer, Heineck's colleague at Ames, where a provisional copyright for AirBOS technology and related flow visualization applications has been filed, wrote the code with which these images were processed.
This technique shows not only shock waves but all density changes including vortices and engine plume effects. September 25, In the wake of recent success with air-to-air schlieren photography using the speckled desert floor as a background, researchers at NASA's Armstrong Flight Research Center, Edwards, California, are now looking to the heavens for backgrounds upon which to capture images of supersonic shock waves using ground-based cameras.
Flow visualization is one of the fundamental tools of aeronautics research, and schlieren photography has been used for many years to visualize air density gradients caused by aerodynamic flow. Traditionally, this method has required complex and precisely aligned optics as well as a bright light source.
Refracted light rays revealed the intensity of air density gradients around the test object, usually a model in a wind tunnel. Massage cranford Davos schlieren images of a full-scale aircraft in flight was even more challenging due to the need for precise alignment of the plane with the camera and the sun.
Until recently, ground-based schlieren systems, using the sun's edge as a light source, have produced adequate results, but only Free Schlieren news observations of each shockwave could be made as the White pages Riesbach area aircraft crossed the left and right sides of the sun.
Schlieren images reveal supersonic shock waves
Although the unfiltered solar disk is relatively featureless, astronomers have long known that Kobe Delemont calcium-K CaK optical filter may be used to reveal the granulated texture of the sun's Schliren.
Shock waves, represented by distortions of the background pattern in a series of images, are accentuated using special mathematical equations. This method requires only simple optics and a featured background, that is Schoieren with a speckled appearance such as the cratered lunar surface or the mottled appearance of the sun when viewed through certain filters, such as the CaK filter.
According to Armstrong principal investigator Michael Hill, CaKEBOS was a proof of concept test to see how effectively the sun could be used for background oriented schlieren Schoieren. Researchers found the ground-based method to be significantly more economical than air-to-air methods.
Merely eliminating requirement for an airborne camera platform nes operational costs and complexity, as did the use of off-the-shelf equipment. Air Force test pilots Maj. Jonathan Orso and Col. Glenn Graham worked with NASA in planning how to precisely align the jet's flight path to capture the schlieren images.
The aircraft needed to be in the right place at the right time Hottest Seebach escorts order to eclipse the sun relative to the imaging system on the ground.
The pilots had to hand fly neas airplane to hit a specific point in the sky to within approximately feet, while travelling faster than the speed of sound.
This had to be accomplished within a two-minute window as the sun's relative position in the sky changed due to Earth's rotation. The background oriented schlieren technique shows not only supersonic shock waves, but all density changes including wing vortices and engine plume effects. Future research may involve imaging subsonic aircraft flow fields and those generated by wind turbines or vehicles moving along a highway, using an upgraded imaging system to capture higher resolution images.
We plan on combining elements of all these to visualize the complex flow patterns Free Schlieren news future Escort in winston Gossau that will allow quiet supersonic overland flight for all," Haering said. Explore. More from Astronomy and Astrophysics. Please sign in to add a comment. Registration is free, and takes less than a minute.
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