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Time-Resolved Piv Measurements for Pressure Distributions around 2d Hydrofoils at Different Cavitation Numbers
|Contributors: ||NTOU:Department of Systems Engineering and Naval Architecture|
|Keywords: ||非侵入式的流體壓力測量;物質加速度;高速PIV;二維水翼;空化;水動力 學|
non-intrusive fluid pressure measurement;material acceleration;Time-Resolved Particle Image Velocimetry;2D hydrofoil;cavitation;hydrodynamics
|Issue Date: ||2013-10-07T02:20:54Z
|Abstract: ||在流體力學中，流體所蘊含的力量與能量，以及與物體或固體邊界的力之關係與交 互作用，一直是在工程上或科學上極重要的課題。舉例來說，航空器與船舶的推進與航 行都是奠基在翼型(foil section)的發展上。翼型為產生升力(lift force)的升力面(lifting surface)，其升力來源為流體通過翼型產生上下表面的壓力差，因此翼型的表現在於其設 計是否能掌握周圍流體的動力特性。另外，在水動力學(hydrodynamics)中有一獨特現 象，即為與液態流體壓力密切相關的空化(cavitation)現象，對水翼(hydrofoil)的表現影響 甚鉅，故使得水翼周圍的流體壓力分佈成為重要的研究議題。 然而測量流體中的壓力是相當不容易的，其困難點在於1.壓力感測器進入流體中皆 會造成侵入性(intrusive)的影響而改變原有的壓力場；2.壓力感測器的尺寸造成其無法解 析特別是紊流場的壓力空間變化。因此，人們開始發展以非侵入式的流場測量技術(PIV) 來測得流體的物質加速度(material acceleration)，再根據Navier-Stokes 方程式推得壓力梯 度的方式獲得流體壓力場分佈。這項技術已在一些具有簡單幾何，或是不會產生空化的 流場中獲得成功，但是還未應用到水翼的水動力學問題上。 回應以上所述之需求，我們計畫用兩年的時間來發展以高速PIV 為主體的流體壓力 測量技術並應用在二維水翼的問題上。第一年先在空蝕水槽中架設一圓柱體，以流通過 圓柱之經典流場來發展、調校並驗證此流體壓力測量技術；第二年則將此技術實際應用 在本實驗室探討過的螺槳，其設計所根據的翼型上，測量這些翼型在不同的空化係數下 的周圍壓力分佈。我們可合理地預期本計畫的成果對於水動力學以及造船工業會有明顯 的助益。|
In fluid mechanics, the force and energy of fluid as well as the forcing interactions between fluid and objects or solid boundaries, are extremely important subjects in engineering and science. For instance, the propulsion and maneuvering of aircrafts and ships has its root on the development of foil sections. Foil sections are lifting surfaces which generate lift forces resulting from the pressure differences between the upper and lower surfaces due to the fluid passing by. Therefore, the performance of a foil section depends on whether its design is capable of harnessing the dynamical characteristics of its surrounding fluid. In addition, a unique phenomenon in hydrodynamics called “cavitation”, which is closely related to the liquid fluid pressure, has huge impacts on the performances of hydrofoils. As a result, pressure distributions around hydrofoils become an important research topic. It is, however, not easy to measure the pressure distribution in a flow field. Its difficulties lie in two major points: 1. that pressure sensors are positioned into flows is intrusive and its consequence is the modification of the original pressure field; 2. the size of pressure sensors is too large to resolve the spatial variations of pressure distributions in especially turbulent flows. Consequently, researchers have started developing techniques of measuring the material acceleration of fluid based on non-intrusive flow measurement techniques (PIV). Once the material acceleration of fluid is obtained, the pressure can be deduced from the pressure gradient term using the balance of the Navier-Stokes equation. This technique has been applied successfully to non-cavitating flow cases of simple geometries. To the best of our knowledge, to date this technique has never been used to address the hydrodynamic problems of hydrofoils. To answer the research demands aforementioned, a two-year project is proposed to develop such a measurement technique of fluid pressure based on the Time-Resolved Particle Image Velocimetry (TR-PIV) and apply it to the flow cases of 2D hydrofoils. In the first year, we will place a round cylinder in our cavitation tunnel and use this canonical flow case to develop, calibrate, and validate our pressure measurement technique. In the second year, this technique will be applied to the flow cases of foil sections at different cavitation numbers. These foil sections are the design basis for the marine propellers we’ve tested before. We are confident that the outcome of this project is able to significantly advance the knowledge of hydrodynamics and the technology of naval architecture.
|Appears in Collections:||[系統工程暨造船學系] 研究計畫|
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