Turbine (II)

choi

(1) Jet Engine Types. Aerospaceweb.org, undated
https://www.aerospaceweb.org/question/propulsion/q0033.shtml
("The key to making a jet engine work is the compression of the incoming air. If uncompressed, the air-fuel mixture won't burn [which is unexplained, but see next sentence] and the engine can't generate any thrust. Most members of the jet family employ a section of compressors, consisting of rotating blades, that slow the incoming air to create a high pressure [it turns out that compressing air creates heat]. * * *  further variation on the turbojet is the turbofan. Although most components remain the same, the turbofan introduces a fan section in front of the compressors. The fan, another rotating series of blades, is also driven by the turbine, but its primary purpose is to force a large volume of air through outer ducts that go around [immediately outside] the engine core [but still within the duct or nacelle]. Although this 'bypassed' air flow travels at much lower speeds * * * A concept similar to the turbofan is the turboprop. However, instead of the turbine driving a ducted fan [fan within a duct], it drives a completely external propeller [outside the nacelle]. * * * In a typical turboprop, the jet core produces about 15% of the thrust while the propeller generates the remaining 85% [the two numbers give you an idea that each contributes to propulsion")

Note:
(a) Home page of this Web site says, "Aerospaceweb.org is a non-profit site operated by engineers and scientists in the aerospace field. The goal of this site is to provide educational information on a variety of subjects ranging from aviation to space travel to aerospace technology."
(b) Please read the entire Web page. Quotation above highlights pitfalls one may encounter.
(c) ducted fan's "primary purpose is to force a large volume of air through outer ducts that go around the engine core. Although this 'bypassed' air flow travels at much lower speeds * * * "
(i) turbofan
https://en.wikipedia.org/wiki/Turbofan

Only watch the animation (at the top of the Wiki page; where single arrow denotes airflow outside nacelle and double arrows, inside nacelle but outside engine core) and two illustrations (whose captions read, respectively, "Schematic diagram illustrating a 2-spool, low-bypass turbofan engine * * * " and "Schematic diagram illustrating a 2-spool, high-bypass turbofan engine * * * ")

Therefore, both low- and high-bypass are housed within the nacelle, though an illustration in the preceding link (www.aerospaceweb.org) shows only the front end of the nacelle that houses high-bypass turbofan.
(ii) nacelle (n; "French, literally, small boat, from Late Latin [noun feminine] navicella ['small ship, boat': Wiktionary], diminutive of Latin [noun feminine] navis ship")
https://www.merriam-webster.com/dictionary/nacelle
(iii) ducted fan
https://en.wikipedia.org/wiki/Ducted_fan

This duct -- outside the fan -- is not called nacelle; I do not know why.
(d) In English, propulsion is the noun of propel. Check their etymology; both English words came from the same Latin verb..


(2) Jet Life with Maggy Blog/Vlog Series. Blazing Trails
https://www.blazingtrails.info/blog

Note: The blog started from the bottom, with the last blog at the top. There is no need to read either (a) to (c) inclusive.
(a) The first blog, dated Aug 31, 2020 and titled "Jet Life with Maggy" started with: "Hey! My name is Maggy Szymanski. I am a new intern here at Larsen Motorsports."

The blog series exemplified General Electric J85
https://en.wikipedia.org/wiki/General_Electric_J85
(turbojet engine; table: First run: 1950s; "The United States Air Force plans to continue using the J85 in aircraft through 2040")
(b) The second blog was dated Sept 16, 2020 and titled "The Jet Age."
(c) The third blog was dated Oct 2, 2020 and titled "Planes to Race Cars."
(d) The fourth blog was dated Oct 28, 2020 and "Anatomy of a Jet Engine: The Compressor Section."
(e) The fifth and last blog was dated Nov 11, 2020 and titled "Combustion Section."

Although the last clause of this blog said "stay tuned for the next vlog and blog about the turbine section!" she did not write it (turbo section).

The fourth and fifth blogs are gems, which are quantitative. However, there is no need to watch videos in the blogs, which is not informative.


(3)
(a) compressor
https://en.wikipedia.org/wiki/Compressor
("A compressor is a mechanical device that increases the pressure of a gas by reducing its volume". section 1 Types: positive displacement and dynamic/ section 3 Temperature: "Compression of a gas increases its temperature"/ section 4 Staged compression)

There is no need to read the text f this Wiki page. A picture is worth a thousand words.
(b) How Air Compressors Work: An Animated Guide. BigRentz, Inc, Jan 3, 2020
https://www.bigrentz.com/blog/how-air-compressors-work

Under the section "Positive Displacement," there is no need to read subsections: "1. Rotary Screw," "2. Rotary Vane" or "3. Reciprocating/Piston Type."

The figure in "Axial Compressors," has step 3 that says, "As the space between fans [of a compressor] get smaller, the high kinetic energy of air causes it to pressurize." HOWEVER, the figure does NOT demonstrate smaller and smaller, but constant, space. This is an error on the part of the figure.

Return to (1) (c)(i) in this blog and you will see in all three (1 animation and 2 illustrations) show the compressor tapers off.

(4) Return to the original question about chicken and egg. When a pilot starts the engine, the process p[rovides energy to turn on compressor, which is then self-perpetuating as long as fuel is injected into the turbine.