Please use this identifier to cite or link to this item:
Applying the Blade Element Momentum Theory to the Computations of Propeller and Current Turbine Forces
|Authors: ||Jian, Xiu-Ting|
|Contributors: ||NTOU:Department of Systems Engineering and Naval Architecture|
propeller;current turbine;momentum theory;blade element method;blade element momentum theory;RANS
|Issue Date: ||2017-11-02T09:04:54Z
|Abstract: ||船用螺槳與洋流渦輪機若應用於黏性流方法進行計算，通常需要耗費較長的 計算時間，尚且還牽涉到網格生成，計算條件設定等等問題，本論文的目的即是 發展一有效率且實用的方法，可以計算螺槳與洋流渦輪機的性能，在未來且可以 應用於在大攻角時的受力，而葉片元素動量法是我們所選擇的方法。葉片元素動 量理論本身為一發展成熟之理論，且已廣泛被應用於風車性能的計算，但對於螺 槳而言，由於螺槳葉片幾何具有較大的面積比，相較於風車之細長型葉片，其三 維效應較強烈，加上所使用之翼型升阻力缺乏一套完整的資料，因此較少人將葉 片元素法應用於螺槳性能計算。本論文一方面推導螺槳之葉片元素動量法理論， 同時也推導洋流渦輪機之理論，我們花費了相當多的時間應用黏性流RANS 方 法建立Modified NACA66 與a = 0.8 拱高翼型的升阻力資料庫。其困難處首先在 於當應用到船用螺槳與洋流渦輪機，計算往往牽涉許多不同厚度，不同拱高的翼 型，建立資料庫需要能夠完整涵蓋這些幾何。其次大攻角與負攻角的計算更是二 維翼型受力計算的挑戰。升阻力資料的不正確會影響葉片元素動量法所計算的結 果之準確性，本論文中應用此資料庫，透過十顆不同螺槳幾何之正車計算，以探 討此資料庫的可信度與缺點所在之處。論文中我們將十顆螺槳的葉片元素動量法 計算值與實驗值進行比較，為了瞭解其誤差，我們將計算值與實驗值之誤差所需 要的修正倍數(係數)進行反算，發現在螺槳正車時，其升力項之修正係數幾乎接 近常數1 倍，表示二維翼型升力的計算較為準確。然而，阻力項之修正係數則不 接近常數1 倍，表示二維翼型阻力計算具有較大的誤差，需要進行更準確的計算。 我們也發現葉片元素法對於單一葉片的面積比較為敏感，表示當螺槳單一葉片面 積比太大時，葉片元素動量法計算的準確度會受到影響。最後，應用此方法於洋 流渦輪機的計算，獲得相同的結論，在大部份的葉尖速度比下，獲得可以接受的 計算結果。|
It is time consuming and complicated to simulate the propeller and current turbine performances by viscous flow RANS method. The objective of this thesis is to develop an efficient and applicable method for the computations of propeller and current turbine performance, and later can be extended to the cases of large angles of attack. The blade element momentum theory (BEMT) is selected as the method in this thesis. The BEMT has been developed for some time, and it is widely used to the evaluation of wind turbine performance. The BEMT is seldom used in evaluating marine propeller performance, and one of the reason is that they usually have stronger three-dimensional effects due to larger area ratios. Also it is not easy to find a complete database of the lift and drag coefficients of two dimensional foils used on propellers. In this thesis, we have first derived formulations of BEMT for both marine propellers and current turbines, and we then spent a lot of time to establish a lift and drag database for modified NACA66 and a=0.8 mean-line sections by using RANS method. The difficulties of establishing this database are first the variations of thickness and camber ratio on propeller and current turbine geometries, and secondly the accurate computations of forces at larger angles of attack. The accuracy of this database directly determine the accuracy of BEMT. In order to understand and investigate the accuracy of our database and BEMT, we have applied the BEMT to the computations of 10 different propeller geometries, and the BEMT results are compared to experimental data. “Correction factors” are defined for both the lift and drag forces, and it is found that the correction factors of the lift are mostly 1 for these 10 propellers, which means the lift coefficients are computed quite accurately. On the other hand, it is not true for drag coefficient computations. The accuracy of drag coefficients has to be improved. It is also found that the BEMT is sensitive to the single blade area ratio, and it is not accurate for propellers with large single blade area ratios. Finally, we have applied BEMT to the computations of current turbine, and similar conclusions are obtained as for the marine propellers. The presented BEMT is feasible for marine propellers and current turbine in forward conditions; however, more efforts are necessary for improving the database accuracies, especially at large angles of attack.
|Appears in Collections:||[系統工程暨造船學系] 博碩士論文|
Files in This Item:
All items in NTOUR are protected by copyright, with all rights reserved.