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本帖最后由 choi 于 12-26-2018 17:02 编辑
This article is interesting. But if you are not into aerospace, you need not read the entire article; the quotations are enough.
Aerospace | Second Time Lucky? A new engine could herald the return of supersonic air travel. Economist, Dec 15, 2018/
https://www.economist.com/scienc ... personic-air-travel
Quote:
(a) "Supersonic passenger travel came to an end in 2003. The crash three years earlier of a French Concorde had not helped, but the main reasons were wider. One was the aircraft’s Rolls-Royce/Snecma Olympus engines, afterburners and all, which gobbled up too much fuel for its flights to be paying propositions. The second was the boom-causing shock wave it generated when travelling supersonically. That meant the overland sections of its route had to be flown below Mach 1. For the Olympus, an engine optimised for travel far beyond the sound barrier, this was commercial death. That, however, was then. And this is now. Materials are lighter and stronger. Aerodynamics and the physics of sonic booms are better understood.
(b) "General Electric (GE) * * * has teamed up with one of the groups of engineers , at Aerion, a company based in Reno, Nevada, to design an engine called affinity * * * [whose] prototypes have [not] been built and tested [and which aims for a top speed of Mach 1.4,] slower than Concord, which could belt along at just over Mach 2.
(c) "Force majeure [(which is sectional heading):] Like all jet engines, Affinity relies for its propulsion on Newton's third law of motion (to every action there is an equal and opposite reaction). The action comes from the mass of air drawn into the engine's front opening being thrust out of the back at far greater velocity. The reaction against thia action propels the engine, and anything attached to it, in the opposite direction -- ie, forward.
"In a simple jet the injected air is first squeezed by a compressor, and then mixed with fuel and ignited in the engine's core to create a fast-moving exhaust. Modern fan jets, however, use some of the exhaust energy to drive a shaft which turns a fan near the engine's intake. That fan pushes a proportion of the incoming air, known as the 'bypass,' around the engine's hot core and out of the back, thus providing additional thrust. Bypass thrust os more economical to create than core thrust, but it i slower moving. A supersonic aircraft can therefore afford only a small bypass ratio (1:1 in the case of many military jets). In a civil airliner the bypass ratio (which, if high, brings not only efficiency but also quietude) may be as great as 10:1.
"Affinity is a compromise between the two approaches, combining technologies from military and civil engines, Though its designers have not revealed its actual ratio(and much else, too, is secret at the moment), they describe it as a 'medium bypass' engine, and have said that it has a bigger fan than any other supersonic engine. Nor does it require an afterburner.
(d) "A particular design challenge, observes Brad Mottier, one of the GE executives leading the project, was that unlike conventional civil jet engines, which hang from an aircraft's wings, Affinity has to blend into a plane's airframe. The law of aerodynamics requires this if it is to perform efficiently. Blending also helps damp down the generation of a sonic boom. Sonic booms are caused by air piling up in front of various parts of the plane, particularly its nose, wings and engine inlets. This air turns into a shock wave that contains a huge amount of energy, which offends the ears when it reaches the ground. Blending engine and body, together design tweaks such as a specially shaped long, thin nose, can muffle a sonic boom befre it gets going. To mute it [sonic boom] after it has happened [there are ways] * * *
My comment:
(a)
(i) I am not interested in sonic boom.
(ii) The discussion will focus on jet engines only, especially how they work.
(iii) More than a decade ago at Mitbbs.com, I had posting about jet engines, who tried his best to comprehend them. One asked what made fan blowing backward rather than forward. It was easy to answer: just like the house fan, whose shape and curvature determine airflow direction. Another asked: in a turbofan, which contributed to engine performance -- was it bypass or hot air created by burned fuel? Now I can answer "both."
(iv) Upon reading the quotations in the Economist, I was awed. Further study shows they (quotations) are ordinary stuff, which, however, will serve as inspiration to understand jet engines.
(b)
(i) turbine (n; First Known Use mid 19th century; from French [noun of the same spelling], from Latin [noun masculine] turbō, turbin- spinning top, whirl [as in tornado, whirlwind]):
"a machine for producing continuous power in which a wheel or rotor, typically fitted with vanes, is made to revolve by a fast-moving flow of water, steam, gas, air, or other fluid"
https://en.oxforddictionaries.com/definition/turbine
(ii) en.wikipedia.org for turbine: section 1 Operational theory: "A working fluid contains potential energy [位能 in Taiwan] (pressure head) and kinetic energy (velocity head)."
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发表于 12-26-2018 15:39:30
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riya JL, Foodie!!!! 