桨叶几何对梢涡空泡起始影响及其机理研究

发布时间：2018-05-26 13:34

本文选题：梢涡 + 梢涡空泡　；参考：《中国舰船研究院》2014年博士论文

【摘要】：随着舰船航速的增加，螺旋桨将先后出现各种不同类型的空泡，舰船的临界航速是指空泡最先起始时的航速，而螺旋桨梢涡空泡由于其尺度效应非常显著，通常是最先起始的空泡。空泡一旦产生，螺旋桨的辐射噪声会显著增加，有时甚至会引起船尾的振动。水面舰船的临界航速是低噪声船舶的重要性能参数，因此，推迟梢涡空泡的起始对于提高舰船的安静性是非常有必要的。在螺旋桨设计中，采用梢部卸载是一种典型的抑制梢涡空泡的有效措施。然而，该措施是以牺牲推进效率为代价的，而且其主要改变的是随边梢涡的强度，对导边涡和局部梢涡的影响不明显。研究桨叶梢部的几何形状，比如侧斜形式、纵倾和厚度分布等参数对推迟梢涡空泡起始的影响也受到了螺旋桨设计者的关注，其工程应用性较强。因此，本文研究的目的是建立一种能够对梢涡空泡起始进行评估的方法，该方法可以对几何变化影响梢涡空泡的起始进行有效性分析，可适用于多方案的相对比较；然后，从梢涡结构和涡核压力等流动机理出发，分析梢部几何形状对梢涡和梢涡空泡起始的影响。目前的研究主要包含了以下几个方面：首先，为了便于分析梢涡的流动结构细节，设计了一只具有现代水面船螺旋桨叶片几何轮廓及负荷特征的三维扭曲水翼，为研究螺旋桨梢涡特征的流动结构提供了很好的对象。并且在中国船舶科学研究中心的空泡水筒利用LDV开展了梢涡区域的流场结构、梢涡轨迹测量和梢涡空泡观测试验，获得了丰富的梢涡速度场分布的数据，也为梢涡流动的数值模拟方法提供了丰富的试验验证数据。其次，采用数值RANS方法模拟了水翼和螺旋桨的梢涡流动，对比分析了不同计算模型对计算结果的影响，认为采用边界层网格和梢涡区域局部加密网格相结合的计算模型更有利于捕捉梢部区域的局部梢涡、导边分离涡等不同类型涡的流动细节。然后，利用这样的计算模型分析了梢部几何参数对梢涡形成和涡流场特征的影响。为了定量评估梢涡空泡的起始，基于CFD计算结果，应用了一个简化的涡模型来计算涡核内的压力分布。针对三维扭曲水翼，通过涡模型计算结果和空泡起始试验测量结果的相关分析，获得了修正系数‘K’。这个修正系数也被应用在了螺旋桨的算例中，与试验结果的比较认为该评估方法可以用来分析评估梢涡空泡抑制效果的有效性，提供了一种可相对比较的方法。在本文的研究中，通过梢部几何的变化来实现抑制和推迟梢涡空泡的起始是最终的研究目标。为此，首先基于所设计的三维扭曲水翼，独立分析了梢部局部的厚度分布变化、侧斜和纵倾形式的变化对梢涡的影响。从流动变化上研究了推迟梢涡空泡起始的机理。梢部几何的变化能够延缓导边分离涡卷入局部梢涡，使得梢部的横向流动减弱。这些变化可以帮助减弱梢涡的强度，延迟梢涡空泡的起始。最后，以三维扭曲水翼的研究结果为基础，针对一个已有的参考螺旋桨，在保持原桨负荷分布不变的条件下，通过改变梢部的几何参数重新设计了一个螺旋桨方案，该梢部几何的变化包括了侧斜形式、纵倾分布和梢部的厚度分布变化。这样的改变目的是为了能够相比于参考桨方案推迟梢涡空泡的起始。在空泡水筒中完成了参考桨和新设计桨的模型试验，，设计目的实现了试验结果的验证，新设计桨的梢涡空泡起始得到了有效的推迟。数值计算结果也反映出了与试验结果相同的趋势，但数值计算结果仍然采用了三维水翼数值分析中相同的经验修正系数，这个修正系数的实用性问题还需要在未来的研究中更进一步的验证。本文的研究指出了一种通过几何变化来推迟梢涡空泡起始的技术方向，根据数值分析结果，在螺旋桨设计阶段能够有效的评估梢涡空泡起始延迟效果的有效性，本文所提出的几何变化措施具有较好的工程应用前景。
[Abstract]:With the increase of ship speed, the propeller will appear a variety of different types of vacuoles. The critical speed of the ship is the first speed when the cavitation first begins, and the propeller tip vortex cavitation is usually the first initiating bubble because of its very significant scale effect. Once the cavitation is produced, the radiation noise of the propeller will increase significantly, sometimes even even if the propeller is produced. It will cause the vibration of the ship's tail. The critical speed of the surface ship is an important performance parameter for the low noise ship. Therefore, it is necessary to postpone the start of the tip vortex vacuole to improve the quietness of the ship. In the design of propeller, the tip unloading is an effective measure to suppress the tip vortex cavitation. However, this measure is sacrificed. The influence of the tip vorticity on the edge vortex and the local tip vortex is not obvious at the cost of advancing efficiency, and the effect of the geometry of the tip of the paddle, such as the lateral form, the longitudinal tilt and the thickness distribution, on the delay of the tip vortex cavitation is also concerned by the propeller designers, and its engineering application Strong.
Therefore, the purpose of this study is to establish a method to evaluate the initiation of tip vortex cavitation. This method can be used to analyze the effect of geometric change on the initiation of tip vortex cavitation, and can be applied to the relative comparison of multiple schemes. Then, the tip geometry of the tip is analyzed from the tip vortex structure and the flow mechanism of the vortex core pressure. The influence of vortex and tip vortex cavitation initiation is studied.
First, in order to facilitate the analysis of the details of the flow structure of the tip vortices, a three-dimensional twisted hydrofoil with the geometric contour and load characteristics of the propeller blade of a modern surface ship is designed. It provides a good object for the study of the flow structure of the tip vortex characteristics of the propeller. The flow field structure of the vortex region, the tip vortex path measurement and the tip vortex cavitation observation test have obtained the abundant data of the tip vortex velocity field distribution, and also provide the abundant experimental verification data for the numerical simulation method of the tip vortex flow.
Secondly, the numerical RANS method is used to simulate the tip vortex flow of hydrofoil and propeller, and the influence of different calculation models on the calculation results is compared and analyzed. It is considered that the combination of boundary layer grid and local encrypted mesh in tip vortex region is more beneficial to capture the local tip vortices in the tip region and the flow of different types of vortices, such as the leading edge separation vortex and other types of vortices. Then, the effect of the geometric parameters of the tip on the tip vortex formation and the characteristics of the eddy current field is analyzed. In order to quantify the initiation of the tip vortex cavitation, a simplified vortex model is applied to calculate the pressure distribution in the vortex core based on the CFD results. The results are calculated by the eddy model for the three-dimensional twisted hydrofoil. The correction coefficient 'K' is obtained by correlation analysis of the measurement results of the initial cavitation test. The correction coefficient is also applied to the example of a propeller. Compared with the experimental results, the method can be used to evaluate the effectiveness of the effect of tip vortex cavitation suppression, and a relative comparison method is provided.
In this study, the ultimate objective of the study is to suppress and delay the initiation of tip vortex vacuoles through the variation of the tip geometry. First, based on the designed three-dimensional twisted hydrofoil, the influence of the variation of the thickness distribution on the tip part of the tip, the variation of the lateral and longitudinal forms on the tip vortices is independently analyzed. The mechanism of the initiation of the tip vortex cavitation. The variation of the tip geometry can delay the involvement of the leading edge vortex into the local tip vortices, making the lateral flow of the tip weakened. These changes can help to weaken the strength of the tip vortices and delay the initiation of the tip vortex vacuoles.
Finally, on the basis of the research results of the three-dimensional twisted hydrofoil, a propeller scheme is redesigned by changing the geometric parameters of the tip of an existing reference propeller to keep the load distribution of the original propeller unchanged. The variation of the tip geometry includes the side slope, the longitudinal inclination distribution and the thickness distribution of the tip. The purpose of the change is to delay the initiation of the tip vortex cavitation in comparison with the reference propeller scheme. The model test of the reference paddle and the newly designed paddle is completed in the vacuolar water tube. The design aims to verify the test results. The tip vortex cavitation in the newly designed paddle has been effectively pushed late. The numerical results also reflect the test knot. The same trend has been achieved, but the numerical results still use the same empirical correction coefficient in the three-dimensional hydrofoil numerical analysis. The practical problem of this correction factor needs to be further verified in future research.
In this paper, a technical direction to delay the initiation of tip vortex cavitation by geometric change is pointed out. According to the results of numerical analysis, the effectiveness of the effect of the initial delay effect on the tip vortex cavitation can be effectively evaluated in the design stage of the propeller. The geometric change measures proposed in this paper have a good prospect for engineering application.
【学位授予单位】：中国舰船研究院
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U664.33;U661.1

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