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Nombor Mach: Perbezaan antara semakan

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Zamwan (bincang | sumb.)
Birokrat, Penyelia
23,017 suntingan
Zamwan (bincang | sumb.)
Birokrat, Penyelia
23,017 suntingan
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Since the speed of sound increases as the temperature increases, the actual speed of an object traveling at Mach 1 will depend on the fluid temperature around it. Mach number is useful because the fluid behaves in a similar way at the same Mach number. So, an aircraft traveling at Mach 1 at sea level (340.3 m/s, 761.2 mph, 1,225 km/h) will experience shock waves in much the same manner as when it is traveling at Mach 1 at 11,000 m (36,000 [[foot (length)|ft]]), even though it is traveling at 295 m/s (654.6 mph, 1,062 km/h, 86% of its speed at sea level).
 
== High-speed flow around objects ==
Kelajuan penerbangan boleh dikelaskan kepada lima kategori:
Flight can be roughly classified in five categories:
* '''[[SubsonicSubsonik]]:''' Ma < 1
* '''[[SonicSonik]]:''' Ma=1
* '''[[TransonicTransonik]]:''' 0.8 < Ma < 1.2
* '''[[SupersonicSupersonik]]:''' 1.2 < Ma < 5
* '''[[HypersonicHipersonik]]:''' Ma > 5
 
(ForUntuk comparisonperbandingan: thekelajuan requireddiperlukan speeduntuk formengorbit [[lowBumi Earthpada orbit]]aras isrendah adalah ca. 7.5 km·s<sup>-1</sup> = Ma 25.4 indalam airudara atpada higharas altitudestinggi)
 
Pada kelajuan transonik, kawasan aliran di sekeliling objek termasuk kedua-dua bahagian subsonik dan supersonik. Tempoh transonik bermula apabila aliran zon pertama Ma>1 muncul di sekeliling objek. Dalam kes di mana ''airfoil'' (seperti sayap pesawat), perkara ini selalunya muncul di atas bahagian sayap. Aliran supersonik hanya boleh diperlahankan semula kepada subsonik dalam kejutan normal; ini biasanya berlaku sebelum hujung ekor. (Rajah 1a)
At transonic speeds, the flow field around the object includes both sub- and supersonic parts. The transonic period begins when first zones of Ma>1 flow appear around the object. In case of an airfoil (such as an aircraft's wing), this typically happens above the wing. Supersonic flow can decelerate back to subsonic only in a normal shock; this typically happens before the trailing edge. (Fig.1a)
 
Apabila halaju meningkat, aliran zon ''Ma''>1 akan meningkat ke arah pinggir depan dan hujung ekor. Setelah ''Ma''=1 dicapai dan dilepasi, kejutan normal mencecah hujung ekor dan menjadi kejutan oblik lemah : aliran nyah-pecut berbanding kejutan, tetapi masih dalam keadaan supersonik. Kejutan normal terbentuk di hadapan objek, dan hanya zon subsonik dalam medan aliran adalah kawasan kecil di sekeliling pinggir depan onjek. (Rajah 1b)
As the velocity increases, the zone of ''Ma''>1 flow increases towards both leading and trailing edges. As ''Ma''=1 is reached and passed, the normal shock reaches the trailing edge and becomes a weak oblique shock: the flow decelerates over the shock, but remains supersonic. A normal shock is created ahead of the object, and the only subsonic zone in the flow field is a small area around the object's leading edge. (Fig.1b)
 
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'''Fig.Rajah 1.''' ''Nombor Mach numberdalam inaliran transonicudara airflowtransonik arounddi ansekeliling ''airfoil''; Ma<1 (a) anddan Ma>1 (b).''
 
Apabila kelajuan pesawat melepasi Mach 1 (iaitu [[tabir bunyi]]) perbezaan tekanan besar terbentuk betul-betul di hadapan [[pesawat]]. Perbezaan tekanan secara tiba-tiba ini, dikenali sebagai [[gelombang kejutan]], merebak kebelakang dan ke arah luar pesawat dalam bentuk kon (juga di kenali sebagai kon Mach). Gelombang kejutan ini akan menghasilkan bunyi [[dentuman sonik]] apabila sebuah pesawat terbang dengan laju. Seseorang yang duduk di dalam pesawat tidak akan mendengar bunyi ini. Lebih tinggi kelajuan pesawat, lebih sempit kon yang terhasil; pada kelajuan sedikit melebihi ''Ma''=1 ia bukan berbentuk seolah-olah kon, tetapi lebih hampir kepada satah cembung.
When an aircraft exceeds Mach 1 (i.e. the [[sound barrier]]) a large pressure difference is created just in front of the [[aircraft]]. This abrupt pressure difference, called a [[shock wave]], spreads backward and outward from the aircraft in a cone shape (a so-called Mach cone). It is this shock wave that causes the [[sonic boom]] heard as a fast moving aircraft travels overhead. A person inside the aircraft will not hear this. The higher the speed, the more narrow the cone; at just over ''Ma''=1 it is hardly a cone at all, but closer to a slightly concave plane.
 
Pada kelajuan supersonik penuh, gelombang kejutan mula membentuk kon, dan aliran sama ada supersonik sepenuhnya, atau (dalam kes objek tumpul), hanya kawasan aliran subsonik kecil kekal di antara muncung objek dan gelombang kejutan terbentuk di hadapannya. (Bagi kes objek berbentuk tajam, tiada udara di antara muncung dan gelombang kejutan: gelombang kejutan bermula daripada muncung.)
At fully supersonic velocity the shock wave starts to take its cone shape, and flow is either completely supersonic, or (in case of a blunt object), only a very small subsonic flow area remains between the object's nose and the shock wave it creates ahead of itself. (In the case of a sharp object, there is no air between the nose and the shock wave: the shock wave starts from the nose.)
 
Apabila nombor Mach meningkat, kekuatan [[gelombang kejutan]] juga meningkat dan kon Mach akan menjadi semakin mengecil. Setelah aliran bendalir melintasi gelombang kejutan, kelajuannya menurun manakala suhu, tekanan dan ketumpatan pula akan meningkat. Semakin kuat gelombang kejutan, semakin besar perubahannya. Pada nombor Mach yang tinggi, kenaikan suhu yang tinggi berbanding kejutan akan memulakan proses mengionkan dan memisahkan molekul-molekul gas di belakang kejutan gelombang. Aliran sebegini dikenali sebagai hipersonik.
As the Mach number increases, so does the strength of the [[shock wave]] and the Mach cone becomes increasingly narrow. As the fluid flow crosses the shock wave, its speed is reduced and temperature, pressure, and density increase. The stronger the shock, the greater the changes. At high enough Mach numbers the temperature increases so much over the shock that ionization and dissociation of gas molecules behind the shock wave begin. Such flows are called hypersonic.
 
Secara jelas, sebarang objek yang merentasi bendalir pada kelajuan hipersonik mungkin akan terdedah pada suhu terlampau yang sama dikenakan pada gas di belakang gelombang kejutan di muncung, oleh itu pemilihan bahan yang mempunyai ketahanan terhadap suhu menjadi amat penting.
It is clear that any object traveling at hypersonic velocities will likewise be exposed to the same extreme temperatures as the gas behind the nose shock wave, and hence choice of heat-resistant materials becomes important.
 
== High-speed flow in a channel ==
Diambil daripada "https://ms.wikipedia.org/wiki/Nombor_Mach"