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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52512

Title: 螺槳片狀空化之實驗探討與模式調校
Experimental Study and Model Calibration on Propeller's Sheet Cavitation
Authors: Lee, Yaw-Huei
李耀輝
Contributors: NTOU:Department of Systems Engineering and Naval Architecture
國立臺灣海洋大學:系統工程暨造船學系
Keywords: 空化發生機率;相位鎖定拍攝;水蒸汽體積分率;非定常片狀空化;螺槳;空化模式
cavitation occurrence probability;phase-locked imaging;vapor volume fraction;unsteady sheet cavitation;propeller;cavitation model
Date: 2017
Issue Date: 2019-11-18T08:16:25Z
Abstract: 船舶螺槳運轉下容易產生多種空化現象(cavitation),而空化現象會影響螺槳的推進效率,甚至可能造成螺槳浸蝕(erosion)損壞與船艙振動噪音等等問題,因此船舶螺槳設計以避免發生空化為主要目標。隨著計算流體力學(computational fluid dynamics)的蓬勃發展,螺槳設計皆會採用其進行螺槳空化的數值模擬與分析,其中最常用的數值模式為RANS (Reynolds-Averaged Navier–Stokes Equation Solver )。然而因為目前的空化實驗方法還是以定性地描述為主,故螺槳空化的實驗結果目前沒有辦法能對數值結果進行量化驗證。 為了達成能對螺槳空化數值結果之量化驗證,本論文首先建立一套相位鎖定拍攝 (phase-locked imaging)系統,應用於一模型螺槳之單獨實驗(open water test) ,拍攝其非定常(unsteady)片狀空化(sheet cavitation)的影像,並經由影像處理及分析程序(image processing and analysis procedure),將空化影像轉化為有物理意義的量化數據:空化發生機率(cavitation occurrence probability, COP);其次,本論文推論RANS數據中的水蒸汽體積分率(vapor volume fraction, VVF)近似於COP。因此,可以直接將RANS所解出的VVF與實驗所獲得的COP進行比對,明確地對數值模式進行量化驗證與修正,解決以往的定性比對之缺陷。 本論文進一步針對相同螺槳進行RANS計算,搭配商用軟體ANSYS FLUENT內建之三種空化數值模式:Singhal 模式、ZGB 模式和SS模式,產生三組VVF分佈。針對VVF與COP量化比對提出兩種量化指標:相關係數(correlation coefficient,CORR)與VVF平均值,其中,相關係數呈現空化分佈上數值VVF與實驗COP結果之相似程度,而VVF平均值與COP平均值的對比則呈現空化數量上之差異。結果得到:Singhal模式的VVF分佈可以達成最大的相關係數值(0.69),其次為ZGB 模式(0.60),而SS模式則差別甚大(0.14);然而三者的VVF平均值皆遠高過COP平均值(0.011)。 最後,再針對三種空化模式的各項可調整係數對結果之影響,進行敏感度分析(sensitivity analysis),作為係數設定依據與調整方向。結果發現:除了SS 模式中的微氣泡數量密度(bubble number density)以外,只要設定值偏離其預設值(default value),所產生的VVF分佈與COP分佈的相關係數就會降低;除了ZGB 模式中的微氣泡直徑(bubble diameter)以外,設定值增加則VVF平均值增加。
Propellers generate multiple types of cavitation when operating. Cavitation affects propulsion efficiency, and even causes erosion and vibration problems. Therefore, avoiding cavitation becomes the main design objective for a propeller. As the CFD (computational fluid dynamics) advances significantly, propeller designers often adopt it for numerically simulating and analyzing cavitation problems of propellers. Nowadays, the RANS (Reynolds-Averaged Navier–Stokes Equation Solver) is the mostly-used computational model in CFD. Due to the fact that the most of propeller experiments of cavitation are qualitative, however, there are no experimental data to quantitatively validate the numerical results. This dissertation firstly establishes a phase-locked imaging system to take images of unsteady sheet cavitation generated by a propeller during its open water test, and then develops an image processing and analysis procedure to transform the cavitation images to quantitative data with physical meaning: the cavitation occurrence probability (denoted as COP). Secondly, the fact that the vapor volume fraction (denoted as VVF) in the RANS can be approximated by the experimental COP is shown, enabling quantitative validation and calibration for numerical models that can’t be achieved with qualitative comparisons between numerical and experimental results. The RANS computations for the same propeller are further conducted with the commercial code ANSYS FLUENT. Three distributions of VVF are generated using three corresponding cavitation models: the models of Singhal, ZGB and SS. They are quantitatively compared with the corresponding COP based on two indicators: the correlation coefficient (the similarity level between distributions) and the average value of VVF (the overall value difference to the COP). The results show that the VVF distribution of the Singhal model has the highest correlation coefficient value of 0.69, while that of the ZGB model has the value of 0.60 and that of the SS model has the lowest value of 0.14. Their average values of VVF are all much larger than that of COP (0.011). Finally, A sensitivity analysis for the adjustable parameters in these three cavitation models is performed to assess their impacts on the results. The results show that except the bubble number density of the SS model, all other parameters yield VVF distributions less correlated with the COP distribution as their values deviate from the default values; except the bubble diameter of the ZGB model, the average value of VVF increases with the values of all other parameters.
URI: http://ethesys.lib.ntou.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=G0D98510003.id
http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52512
Appears in Collections:[系統工程暨造船學系] 博碩士論文

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