나사의 놀라운 초음속 돌파 이미지 현상 The supersonic images that could pave the way for the ‘son of Concorde’: Incredible photos captures the sonic boom of aircraft(VIDEO)

The supersonic images that could pave the way for the ‘son of Concorde’: Incredible photos captures the sonic boom of aircraft 나사의 놀라운 초음속 돌파 이미지 현상 

극초음속 여객기 개발을 위한  나사의 놀라운 초음속 돌파 이미지 현상 나사는 이를 위해 150년된 일명 '슐리렌' 이미지 형상화 기술를 사용하고 있다. 이 기술은 공중에서의 굴절율의 변화를 보여준다. 나사는 소닉붐의 노이즈(소음)의 크기를 줄이는데 도움을 줄 것으로 기대하고 있다. * 충격파(shock wave) 초음속 물질이 지나가는 순간 주변 공기가 압축되어 급속히 전파되는 강력한 파장이 바로 충격파(shock wave)이다. 번개가 칠 때 탄환이 날아갈 때 그리고 핵폭탄이 폭발하는 순간 발생하며, 전투기가 초음속으로 속도를 높일 때도 발생하게 된다.  * 소닉붐(sonic boom) 초음속 비행기가 내는 큰 소음 제트기 등이 비행 중에 음속(音速)을 돌파하거나 음속에서 감속했을 때 또는 초음속 비행을 할 때 생기는 충격파가 지상에 도달하여 일으키는 큰 충격음을 말한다. 비행기가 초음속을 돌파할 때 충격파가 생기는데 이것은 비행기의 앞머리를 정점으로 하여 원추형으로 확장되는 강한 파장을 이루며 전달된다. 7,500m 이하로 비행할 경우 소닉 붐은 유리창을 깨뜨리고 심할 때엔 건축물에도 손상을 가한다. by Ki Chul Hwang  Conpaper  Editor Distributor  황기철  콘페이퍼 에디터

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Nasa is using a 150-year-old technique dubbed 'schlieren imagery'

This helps seeing changes in what is known as the refractive index of air

Nasa is hoping it will help model how to reduce the noise of sonic booms

By ELLIE ZOLFAGHARIFARD FOR DAILYMAIL.COM

Nasa is using a 150-year-old photography technique to capture stunning images of shockwaves created by supersonic planes.

The technique, dubbed 'schlieren imagery', involves seeing changes in what is known as the refractive index of air – or the speed of light in a given medium.

Because shock waves represent an obvious and sudden change in the refractive index, they can be seen clearly in schlieren photographs.

The space agency is hoping the technique will help it model how to reduce the noise of sonic booms and pave the way for the 'son of Concorde'.

Scroll down for video 

This schlieren image dramatically displays the shock wave of a supersonic jet flying over the Mojave Desert. Researchers used Nasa -developed image processing software to remove the desert background, then combined and averaged multiple frames to produce a clear picture of the shock waves

 

WHAT IS SCHLIEREN IMAGING?

Schlieren photography was invented in 1864 by German physicist August Toepler. 

The technique involves seeing changes in what is known as the refractive index of air – or the speed of light in a given medium.

Because shock waves represent an obvious and sudden change in the refractive index, they can be seen clearly in schlieren photographs.

Nasa is hoping the technique will help it model how shockwaves form by supersonic aircraft, in an effort to reduce the noise of sonic booms.

'Lessening sonic booms is the most significant hurdle to reintroducing commercial supersonic flight,' according Peter Coen, head of the High Speed Project at Nasa.

Schlieren photography was invented in 1864 by German physicist August Toepler, but is usually used to image shock waves of small-scale aircraft models in wind tunnels.

But in recent years, Nasa has been developing new types of schlieren techniques to capture shock waves of full-size aircraft in flight.

One such technique, called background oriented schlieren (BOS), has been particularly successful in wind tunnel tests.

First, researchers obtain an image of a speckled background pattern, and then they collect a series of images of an object in supersonic flow in front of the same pattern.

Shock waves can be seen from distortions of the background pattern.

In April 2011 the first phase of air-to-air flight-testing at Armstrong, dubbed AirBOS 1, proved the feasibility of using the BOS technique for imaging supersonic shock waves created by a Nasa F-18.

A high-speed camera on the underside of a Nasa Beechcraft B200 King Air captured 109 frames per second while the supersonic target aircraft passed several thousand feet underneath in straight-and-level flight at speeds up to Mach 1.09.

'Air-to-air schlieren is an important flight-test technique for locating and characterising, with high spatial resolution, shock waves emanating from supersonic vehicles,' said Dan Banks, Armstrong's principal investigator on the project.

Nasa is using a 21st century version of schlieren imagery, invented by a German physicist in 1864, to visualise supersonic flow phenomena with full-scale aircraft in flight

QUIETENING THE SONIC BOOM 

In a conventional supersonic aircraft, shockwaves from the nose, cockpit, inlets, wings and other features come together as they move through the atmosphere into strong shocks emanating from the nose and tail.

These are known as bow and tail shocks, respectively.

As these shockwaves pass over someone on the ground, air pressure rises sharply, declines, then rises rapidly again - it’s this that produces the classic ‘double-bang’ sonic boom.

Reshaping the aircraft to produce a longer, more slender shape that slips through the air is the best way to generate shockwaves of lower, more equal strength that attenuate as they pass through the atmosphere and do not form into such strong bow and tail shocks.

Nasa says stretching the nose to break the bow shock into a series of weaker shockwaves is particularly effective. This lowers and spreads that initial pressure peak and softens the first bang of the sonic boom.

'It allows us to see the shock wave geometry in the real atmosphere as the target aircraft flies through temperature and humidity gradients that cannot be duplicated in wind tunnels.'

'After much planning and a little luck we were able to acquire in-flight images and process the data, 

achieving results the first time out,' said J.T. Heineck, the Masa Ames principal investigator.

This technique shows not only shock waves but all density changes including vortices and engine plume effects. Future work may include imaging subsonic aircraft flow fields.

Researchers continued to refine and improve techniques during the AirBOS 3 series in February this year.

Supersonic target aircraft included a Nasa F-15 and a T-38C from the Air Force Test Pilot School (TPS) at Edwards.

Following each flight the AirBOS team used Nasa-developed image processing software to remove the desert background and reveal rough shock wave images.

Next, researchers combined and averaged multiple frames to produce clean and clear images of the shock waves.

'It is hoped that the AirBOS images can be used to validate or improve current design techniques,' said Brett Pauer, CST project support manager at Armstrong.

A T-38C from the Air Force Test Pilot School served as a target for Nasa's schlieren imaging system. Researchers continued to refine and improve techniques during the AirBOS 3 series in February

DAILYMAIL

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