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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Pitot tube ： ウィキペディア英語版 Pitot tube A pitot ( ) tube is a pressure measurement instrument used to measure fluid flow velocity. The pitot tube was invented by the French engineer Henri Pitot in the early 18th century and was modified to its modern form in the mid-19th century by French scientist Henry Darcy. It is widely used to determine the airspeed of an aircraft, water speed of a boat, and to measure liquid, air and gas flow velocities in industrial applications. The pitot tube is used to measure the local flow velocity at a given point in the flow stream and not the average flow velocity in the pipe or conduit. ==Theory of operation== The basic pitot tube consists of a tube pointing directly into the fluid flow. As this tube contains fluid, a pressure can be measured; the moving fluid is brought to rest (stagnates) as there is no outlet to allow flow to continue. This pressure is the stagnation pressure of the fluid, also known as the total pressure or (particularly in aviation) the pitot pressure. The measured stagnation pressure cannot itself be used to determine the fluid flow velocity (airspeed in aviation). However, Bernoulli's equation states: Stagnation pressure = static pressure + dynamic pressure Which can also be written :$p\_t\; =\; p\_s\; +\; \backslash left(\backslash frac\backslash right)$ Solving that for flow velocity: :$u\; =\; \backslash sqrt\}$ NOTE: The above equation applies only to fluids that can be treated as incompressible. Liquids are treated as incompressible under almost all conditions. Gases under certain conditions can be approximated as incompressible. See Compressibility. where: * $u$ is flow velocity to be measured in m/s; * $p\_t$ is stagnation or total pressure in pascals; * $p\_s$ is static pressure in pascals; * and $\backslash rho$ is fluid density in $kg/m^3$. The dynamic pressure, then, is the difference between the stagnation pressure and the static pressure. The dynamic pressure is then determined using a diaphragm inside an enclosed container. If the air on one side of the diaphragm is at the static pressure, and the other at the stagnation pressure, then the deflection of the diaphragm is proportional to the dynamic pressure. In aircraft, The static pressure is generally measured using the static ports on the side of the fuselage. The dynamic pressure measured can be used to determine the indicated airspeed of the aircraft. The diaphragm arrangement described above is typically contained within the airspeed indicator, which converts the dynamic pressure to an airspeed reading by means of mechanical levers. Instead of separate pitot and static ports, a pitot-static tube (also called a Prandtl tube) may be employed, which has a second tube coaxial with the pitot tube with holes on the sides, outside the direct airflow, to measure the static pressure.〔("How Aircraft Instruments Work." ) ''Popular Science'', March 1944, pp. 116.〕 If a liquid column manometer is used to measure the pressure difference $p\_t$ – $p\_s$, or $\backslash Delta\; p$, :$\backslash Delta\; h\; =\; \backslash frac$ where: * $\backslash Delta\; h$ is the height difference of the columns in meters. * $\backslash rho\_l$ is the density of the liquid in the manometer; * g is the acceleration of gravity in $m/s^2$ Therefore :$V\; =\; \backslash sqrt\}$ 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pitot tube」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.