當『螺旋槳』
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid (such as air or water) is accelerated behind the blade. Propeller dynamics, like those of aircraft wings, can be modelled by Bernoulli’s principle and Newton’s third law. Most marine propellers are screw propellers with fixed helical blades rotating around a horizontal (or nearly horizontal) axis or propeller shaft.
History
Early developments
The principle employed in using a screw propeller is used in sculling. It is part of the skill of propelling a Venetian gondola but was used in a less refined way in other parts of Europe and probably elsewhere. For example, propelling a canoe with a single paddle using a“pitch stroke” or side slipping a canoe with a “scull” involves a similar technique. In China, sculling, called “lu”, was also used by the 3rd century AD.
In sculling, a single blade is moved through an arc, from side to side taking care to keep presenting the blade to the water at the effective angle. The innovation introduced with the screw propeller was the extension of that arc through more than 360° by attaching the blade to a rotating shaft. Propellers can have a single blade, but in practice there are nearly always more than one so as to balance the forces involved.
The origin of the screw propeller starts with Archimedes, who used a screw to lift water for irrigation and bailing boats, so famously that it became known as Archimedes’ screw. It was probably an application of spiral movement in space (spirals were a special study of Archimedes) to a hollow segmented water-wheel used for irrigation by Egyptians for centuries. Leonardo da Vinci adopted the principle to drive his theoretical helicopter, sketches of which involved a large canvas screw overhead.
In 1661, Toogood and Hays proposed using screws for waterjet propulsion, though not as a propeller.[1] Robert Hook in 1681 designed a horizontal watermill which was remarkably similar to the Kirsten-Boeing vertical axis propeller designed almost two and a half centuries later in 1928; two years later Hook modified the design to provide motive power for ships through water.[2] In 1752, the Academie des Sciences in Paris granted Burnelli a prize for a design of a propeller-wheel. At about the same time, the French mathematician Alexis-Jean-Pierre Paucton, suggested a water propulsion system based on the Archimedean screw.[3] In 1771, steam-engine inventor James Watt in a private letter suggested using “spiral oars” to propel boats, although he did not use them with his steam engines, or ever implement the idea.[4]
The first practical & applied use of a propeller on a submarine dubbed the Turtle which was designed in New Haven, Connecticut, in 1775 by Yale student and inventor David Bushnell, with the help of the clock maker, engraver, and brass foundryman Isaac Doolittle, and with Bushnell’s brother Ezra Bushnell and ship’s carpenter and clock maker Phineas Pratt constructing the hull in Saybrook, Connecticut.[5][6] On the night of September 6, 1776, Sergeant Ezra Lee piloted the Turtle in an attack on the HMS Eagle in New York Harbor.[7][8] The Turtle also has the distinction of being the first submarine used in battle. Bushnell later described the propeller in an October 1787 letter to Thomas Jefferson: “An oar formed upon the principle of the screw was fixed in the forepart of the vessel its axis entered the vessel and being turned one way rowed the vessel forward but being turned the other way rowed it backward. It was made to be turned by the hand or foot.”[9] The brass propeller, like all the brass and moving parts on the Turtle, was crafted by the “ingenious mechanic” Issac Doolittle of New Haven.[10]
In 1785, Joseph Bramah in England proposed a propeller solution of a rod going through the underwater aft of a boat attached to a bladed propeller, though he never built it.[11] In 1802, Edward Shorter proposed using a similar propeller attached to a rod angled down temporarily deployed from the deck above the waterline and thus requiring no water seal, and intended only to assist becalmed sailing vessels. He tested it on the transport ship Doncaster in Gibraltar and at Malta, achieving a speed of 1.5 mph.[12]
The lawyer and inventor John Stevens in the USA, built a 25-foot boat with a rotary stem engine coupled to a four-bladed propeller, achieving a speed of 4 mph, but he abandoned propellers due to the inherent danger in using the high-pressure steam engines, and instead built paddle-wheeled boats.[13]
By 1827, Czech-Austrian inventor Josef Ressel had invented a screw propeller which had multiple blades fastened around a conical base. He had tested his propeller in February 1826 on a small ship that was manually driven. He was successful in using his bronze screw propeller on an adapted steamboat (1829). His ship “Civetta” with 48 gross register tons, reached a speed of about six knots (11 km/h). This was the first ship successfully driven by an Archimedes screw-type propeller. After a new steam engine had an accident (cracked pipe weld) his experiments were banned by the Austro-Hungarian police as dangerous. Josef Ressel was at the time a forestry inspector for the Austrian Empire. But before this he received an Austro-Hungarian patent (license) for his propeller (1827). He died in 1857. This new method of propulsion was an improvement over the paddlewheel as it was not so affected by either ship motions or changes in draft as the vessel burned coal.[14]
John Patch, a mariner in Yarmouth, Nova Scotia developed a two-bladed, fan-shaped propeller in 1832 and publicly demonstrated it in 1833, propelling a row boat across Yarmouth Harbour and a small coastal schooner at Saint John, New Brunswick, but his patent application in the United States was rejected until 1849 because he was not an American citizen.[15] His efficient design drew praise in American scientific circles[16] but by this time there were multiple competing versions of the marine propeller.
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遇上
白努利定律
白努利原理（英語：Bernoulli’s principle），又稱柏努利定律、白努利定律（英語：Bernoulli’s Law）[1]，是流體力學中的一個定律 ，由瑞士流體物理學家丹尼爾·白努利於1738年出版他的理論《Hydrodynamica》，描述流體沿著一條穩定、非黏性、不可壓縮的流線移動行為。[2]
在流體動力學，白努利原理指出，無黏性的流體的速度增加時，流體的壓力能或位能（位能）總和將減少。
白努利原理可以應用到不同類型的流體流動，從而是可廣泛套用的白努利方程式表示式。事實上，有不同類型的流的白努利方程式的不同形式的。白努利原理的簡單形式是有效的不可壓縮流動（如最液體流動），也為移動可壓縮流體（如氣體）在低馬赫數（通常小於0.3）。更先進的形式可被應用到在某些情況 下，在更高的馬赫數（見白努利方程式的推導）可壓縮流。
白努利定律可以從能量守恆定律來推演。說明如下：在一個穩定的水流，沿著直線流向的所有點上，各種形式的流體機械能總和必定相同。也就是說，動能，位能，與內能的總和保持不變。換言之，任何的流體速度增加，即代表動態壓力和單位體積動能的增加，而在同時會導致其靜態壓力，單位體積流體的位能、內能等三者總和的減少。如果液體流出水庫，在各方向的流線上，各種形式的能量的總和是相同的；因為每單位體積能量的總和（即壓力和單位體積流體的重力位能 
的總和 ）在水庫內的任何位置都相同。
白努利原理，也可以直接由牛頓第二定律推演。說明如下：如果從高壓區域往低壓區域，有一小體積流體沿水平方向流動，小體積區域後方的壓力自然比前方區域的壓力更大。所以，此區域的力量總和必然是沿著流線方向向前。在此假設，前後方區域面積相等，如此便提供了一個正方向淨力施於原先設定的流體小體積區域，其加速度與力量同方向。此假想環境中，流體粒子僅受到壓力和自己質量的重力之影響。先假設如果流體沿著流線方向作水平流動，並與流體流線的截面積垂直，因為流體從高壓區域朝低壓區域移動，流體速度因此增加；如果該小體積區域的流速降低，其唯一的可能性必定是因為它從低壓區朝高壓區移動。因此 ，任一水平流動流體之內，壓力最低處有最高流速，壓力最高處有最低流速。
水流進入文丘裡計。在不計流體壓力下而增加動能，如圖中兩列管的高度差。
物理量及定律
原表達形式
其中：
定理假設
使用白努利定律必須符合以下假設，方可使用；如沒完全符合以下假設，所求的解也是近似值。
- 定常流動（或稱穩定流，Steady flow）：在流動系統中，流體在任何一點之性質不隨時間改變。
- 不可壓縮流（Incompressible flow）：密度為常數，在流體為氣體適用於馬赫數
小於0.3的情況。 - 無摩擦流（Frictionsless flow）：摩擦效應可忽略，忽略黏滯性效應。
- 流體沿著流線流動（Flow along a streamline）：流體元素（element）沿著流線而流動，流線間彼此是不相交的。
快慢流速激發『轉子』產生了『推進力』！
默然咀嚼阿基米德提水器其中味？
回旋反思，就算『數理完備』
Blade element momentum theory
Blade element momentum theory is a theory that combines both blade element theory and momentum theory. It is used to calculate the local forces on a propeller or wind-turbine blade. Blade element theory is combined with momentum theory to alleviate some of the difficulties in calculating the induced velocities at the rotor.
This article emphasizes application of BEM to ground-based wind turbines, but the principles apply as well to propellers. Whereas the streamtube area is reduced by a propeller, it is expanded by a wind turbine. For either application, a highly simplified but useful approximation is the Rankine–Froude “momentum” or “actuator disk” model (1865,1889). This article explains the application of the “Betz limit” to the efficiency of a ground-based wind turbine.
A development came in the form of Froude’s blade element momentum theory (1878), later refined by Glauert (1926). Betz (1921) provided an approximate correction to momentum “Rankine–Froude actuator-disk” theory to account for the sudden rotation imparted to the flow by the actuator disk (NACA TN 83, “The Theory of the Screw Propeller” and NACA TM 491, “Propeller Problems”). In blade element momentum theory, angular momentum is included in the model, meaning that the wake (the air after interaction with the rotor) has angular momentum. That is, the air begins to rotate about the z-axis immediately upon interaction with the rotor (see diagram below). Angular momentum must be taken into account since the rotor, which is the device that extracts the energy from the wind, is rotating as a result of the interaction with the wind.
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如何『傳播大眾』？？普照於人呀！！
