دوي إختراق الصوت

من أجل استخدامات أخرى، انظر دوي إختراق الصوت (توضيح).

Rapid condensation of water vapor due to a sonic shock produced at sub-sonic speed creates a vapor cone (known as a Prandtl–Glauert singularity), which can be seen with the naked eye

A sonic boom produced by an aircraft moving at M=2.92, calculated from the cone angle of 20 deg. An observer hears the boom when the shock wave, on the edges of the cone, crosses his or her location.

Mach cone angle

يستعمل مصطلح دوي إختراق الصوت ليشير إلى الدوي الناتج عن إقلاع طائرة أسرع من الصوت. ويشبه ذلك الصوت بالنسبة لشخص على الأرض صوت قصف الرعد. وهذا الصوت نتيجة للموجة التصادمية التي تسببها الطائرة. وهذه الموجة اضطراب في الضغط ينشأ حول الطائرة المحلِّقة بسرعة تفوق سرعة الصوت بسبب اختلاف طريقة تدفق الهواء حول مقدمة الحواف الرئيسية للطائرة. وهذا الدوي غير ضار بالإنسان، إلا أنه يسبّب تشققات في الجدران، وقد يحطم زجاج النوافذ. ويقال عن الطائرة التي تتجاوز سرعة الصوت إنها تحطم حاجز الصوت.

ويعتبر الكابتن تشارلز إلوود ييجر من القوات الجوية الأمريكية أول من حطم حاجز الصوت على متن طائرة صاروخية منطراز بِل اكس-1 في 14 اكتوبر عام 1947م.

الأسباب

$\sin \left(\alpha \right)=\frac{1}{M}$,

حيث M هي عدد ماخ للطائرة. So the faster it goes, the finer, (more pointed) the cone.

وتسمى النسبة بين سرعة الطائرة وسرعة الصوت في الهواء عدد ماخ Mach number. ولما كان المخروط يتحرك بتحرك الطائرة، فإن خط تقاطعه مع سطح الأرض يأخذ شكل قطع مكافئ، ومن ثم فكل مَن هو موجود على هذا القطع يسمع الأزيز الصوتي. وبالطبع فإن شدة الأزيز أو مقدار ازدياد ضغط الهواء يضعف بازدياد البعد عن الطائرة، ويتغير بتغير حجمها ووزنها وشكلها، كما يتأثر بالظروف الجوية السائدة وبعوامل أخرى.

الشكل (2) جدار الصوت

إن بالإمكان التنبؤ بمقدار ازدياد ضغط الهواء الناشئ عن الأزيز الصوتي على طول خط سير محدد لطائرة تنطلق بسرعة تفوق سرعة الصوت فيه، وبما ينجم عن ذلك من أضرار كتحطُّم النوافذ، وإحداث شقوق دقيقة في الورق الذي يكسو الجدران. وقد بيَّنت الدراسات أن الأضرار تكون معدومة إذا قل ازدياد الضغط عن 7.3كيلو غراماً على المتر المربع. إلا أن ما يشغل بال الباحثين هو الآثار النفسية المترتِّبة على تكرار سماع الأزيز الصوتي خاصةً عندما يحدث ذلك فوق مناطق مأهولة بالسكان ومن طائرات نقل تحلِّق بسرعات تفوق سرعة الصوت ultrasonic.

تجدر الإشارة إلى أن المخروط الذي تتوضَّع عليه موجة الصدم يؤول إلى مستوٍ عندما تبلغ سرعةُ الطائرة سرعة الصوت في الهواء تماماً، ويشكِّل المستوي عندها جداراً عند مقدِّمة الطائرة يدعى جدار الصوت يتقدم بتقدم الطائرة، ويحدث في موضع تلاقيه مع سطح الأرض أزيزاً صوتياً كالأزيز الذي يولِّده مخروط موجة الصدم، ويسود عندها هدوء أمام هذا الجدار فلا يَسمع صوت الطائرة مَن كان واقفاً أمامه.

الأمثلة والقياس

الطائرة	السرعة	الارتفاع	الضغط (psf)
اس ار 71	3 ماخ	80,000 قدم	0.9
كونكورد SST	2 ماخ	52,000	1.94
اف 104	1.93 ماخ	48,000 قدم	0.8
مكوك فضاء	1.5 ماخ	60,000 قدم	1.25

الحد من الدوي

New research is being performed at NASA's Glenn Research Center that could help alleviate the sonic boom produced by supersonic aircraft. Testing was completed in 2010 of a Large-Scale Low-Boom supersonic inlet model with micro-array flow control. A NASA aerospace engineer is pictured here in a wind tunnel with the Large-Scale Low-Boom supersonic inlet model.

In the late 1950s when supersonic transport (SST) designs were being actively pursued, it was thought that although the boom would be very large, the problems could be avoided by flying higher. This assumption was proven false when the North American XB-70 Valkyrie first flew, and it was found that the boom was a problem even at 70,000 feet (21,000 m). It was during these tests that the N-wave was first characterized.

Richard Seebass and his colleague Albert George at Cornell University studied the problem extensively and eventually defined a "figure of merit" (FM) to characterize the sonic boom levels of different aircraft. FM is a function of the aircraft's weight and the aircraft length. The lower this value, the less boom the aircraft generates, with figures of about 1 or lower being considered acceptable. Using this calculation, they found FMs of about 1.4 for Concorde and 1.9 for the Boeing 2707. This eventually doomed most SST projects as public resentment, mixed with politics, eventually resulted in laws that made any such aircraft less useful (flying supersonically only over water for instance). Small airplane designs like business jets are favored and tend to produce minimal to no audible booms.

Building on the earlier research of L. B. Jones, Seebass, and George identified conditions in which sonic boom shockwaves could be eliminated. This work was extended by Christine. M. Darden and described as the Jones-Seebass-George-Darden theory of sonic boom minimization. This theory, approached the problem from a different angle, trying to spread out the N-wave laterally and temporally (longitudinally), by producing a strong and downwards-focused (SR-71 Blackbird, Boeing X-43) shock at a sharp, but wide angle nose cone, which will travel at slightly supersonic speed (bow shock), and using a swept back flying wing or an oblique flying wing to smooth out this shock along the direction of flight (the tail of the shock travels at sonic speed). To adapt this principle to existing planes, which generate a shock at their nose cone and an even stronger one at their wing leading edge, the fuselage below the wing is shaped according to the area rule. Ideally, this would raise the characteristic altitude from 40،000 أقدام (12،000 m) to 60,000 feet (from 12,000 m to 18,000 m), which is where most SST aircraft were expected to fly.

NASA F-5E modified for DARPA sonic boom tests

This remained untested for decades, until DARPA started the Quiet Supersonic Platform project and funded the Shaped Sonic Boom Demonstration (SSBD) aircraft to test it. SSBD used an F-5 Freedom Fighter. The F-5E was modified with a highly refined shape which lengthened the nose to that of the F-5F model. The fairing extended from the nose back to the inlets on the underside of the aircraft. The SSBD was tested over two years culminating in 21 flights and was an extensive study on sonic boom characteristics. After measuring the 1,300 recordings, some taken inside the shock wave by a chase plane, the SSBD demonstrated a reduction in boom by about one-third. Although one-third is not a huge reduction, it could have reduced Concorde's boom to an acceptable level below FM = 1.

As a follow-on to SSBD, in 2006 a NASA-Gulfstream Aerospace team tested the Quiet Spike on NASA Dryden's F-15B aircraft 836. The Quiet Spike is a telescoping boom fitted to the nose of an aircraft specifically designed to weaken the strength of the shock waves forming on the nose of the aircraft at supersonic speeds. Over 50 test flights were performed. Several flights included probing of the shockwaves by a second F-15B, NASA's Intelligent Flight Control System testbed, aircraft 837.

Some theoretical designs do not appear to create sonic booms at all, such as the Busemann biplane. However, creating a shockwave is inescapable if it generates aerodynamic lift.

In 2018, NASA awarded Lockheed Martin a $247.5 million contract to construct a design known as the Low Boom Flight Demonstrator, which aims to reduce the boom to the sound of a car door closing. As of October 2023, the first flight was expected in 2024.

السوط

An Australian bullwhip

The cracking sound of a bullwhip is a small sonic boom. The end of the whip, known as the "cracker", moves faster than the speed of sound, thus creating a sonic boom.

A bullwhip tapers down from the handle section to the cracker. The cracker has much less mass than the handle section. When the whip is sharply swung, the momentum is transferred down the length of the tapering whip, the declining mass being made up for with increasing speed. Goriely and McMillen showed that the physical explanation is complex, involving the way that a loop travels down a tapered filament under tension.

انظر أيضا

• Supersonic transport
• حاجز الصوت
• كونكودر
• Quiet Spike

المصادر

4. Crackin' Good Mathematics