【作者】 尹冬梅；

【导师】 钱林方；

【作者基本信息】 南京理工大学 ， 机械设计及理论， 2009， 博士

【摘要】 高速旋转的叶轮机械叶片常受到随气流吸入的金属物、砂石、冰雹等外物的损伤,从而使叶轮机械性能下降,影响正常使用,甚至导致灾难性事故。本文结合国内外叶片外物损伤的实验研究及数值分析方面的成果,借助现代先进的计算技术、分析方法,针对外物的形状、材料、叶片的运动及结构预应力等不同撞击环境因素的影响下,高速旋转叶片的外物损伤问题,进行研究和讨论,旨在建立一个较完整、系统的高速旋转叶片外物损伤的分析框架和分析方法,并取得了一些有用的结论,从而为高速旋转叶片的结构抗撞设计与优化提供相应的参考依据。首先对平板叶片进气边的钢球撞击试验在LS-DYNA中进行了数值模拟,获得可靠的相关参数。综合运用显、隐式有限元算法进行了叶片进气边受不同形状外物撞击的瞬态显式分析和受撞击后叶片中残余应力场的静态计算,得出了不同的外物形状对叶片受撞击后的损伤的影响规律。基于能量分析的方法和板壳理论对叶片曲率对叶片外物撞击损伤的相关特征的影响进行分析,重点研究了叶片变形能与叶片曲率之间的关系。采用不同曲率半径的悬臂板模拟叶片,研究了外物撞击不同曲率的叶片凹面和凸面的撞击特征,获得了叶片曲率半径对叶片外物撞击损伤的一些影响规律。分别采用能量守恒、弹性应力波的传播及基本水动力学的原理分析了硬体、超弹性软体及塑性软体外物撞击叶片时的撞击载荷。对超弹性软体(橡胶)和塑性软体(明胶)低速撞击刚性墙进行数值模拟与验证。并对这两种软体撞击叶片进气边进行了数值分析,仿真结果表明,撞击过程中这两种软体外物均出现了被切割的现象,并且在同一撞击条件下,橡胶撞击明显比明胶撞击对叶片的损伤大。在相同的初始撞击能量及入射角度下,以砂石、橡胶和明胶分别作为硬体、超弹性软体及塑性软体外物进行外物撞击叶片的数值分析与比较,得到了相同撞击条件下,叶片受不同材料的外物撞击的有关撞击特征规律。采用显-隐式的转换算法,对叶片受不同材料的外物撞击损伤前后的模态特性进行了研究,结果表明外物损伤对叶片的固有频率影响较大,对其模态振型影响不大。基于Lamb问题的应力波分析理论对叶片外物撞击瞬间,叶片内激发的应力波种类、先后顺序及其对叶片可能产生的损伤进行分析；结合数值方法对叶片中应力波的传播与作用特征及其影响的因素(撞击载荷模型和应变率效应)进行了研究,结果表明撞击载荷模型的不同,导致叶片所受的入射应力波的幅值和波长不一样；应变率效应的存在,使得叶片中应力波的幅值明显提高,而衰减速度减小,反射应力波幅值也相应地变大。基于终点弹道学中运动靶的弹丸非理想撞击的分析原理,建立了旋转运动的叶片受外物撞击损伤的分析模型,研究了叶片的旋转运动对叶片受外物损伤的影响规律。建立了结构预应力(主要是离心预应力)作用下叶片外物撞击的非线性动力学模型。提出采用动力松弛的方法在撞击分析之前对叶片结构进行应力和位移场的初始化。结合应力波传播的相关理论,对不同转速下的实际叶片模型进行外物撞击的数值分析,获得了不同离心预载作用下外物损伤的一些规律。最后,以M20螺栓和橡胶残骸分别作为硬体外物和软体外物的代表,进行多个旋转叶片的外物撞击损伤分析,比较了两者撞击多个旋转叶片时的撞击特征的区别。更多还原

【Abstract】 The blades of impeller machinery with high rotating speed are often damaged by foreign objects such as metal,sandstone,hailstone,which are ingested with airflow. It can lead to a degradation in the machine’s performance and affect its normal working, even cause catastrophic accidents.According to the research findings of foreign objects damage(FOD) of blades on experiments and numerical analysis, analysis for the FOD of blades under various impact conditions is conducted by using the advanced computing techniques and analytical procedures. These impact conditions include various shapes and materials of foreign objects,motion and structural prestress of blades. The present dissertation aims at exploring a suit of integrated and systematic method for FOD of blades, and obtaining some useful conclusions, thus offering an important reference for the investigation of anti-impacting damage of blades under foreign object damage and structure optimization of blades.Firstly,the experiment for the steel sphere impacting on the leading edge of flat blade is simulated in the LS-DYNA.It provides reliable correlative parameters for the following analysis.Dynamic analysis for the leading edge of blades impacted with foreign objects with different shapes and static calculation for residual stress of the blades after impacting are done by combining Explicit and implicit analysis. An analysis based on energy method and the theory for plate and shell is conducted to explain the influence of blade’s curvature on the impact damage characteristics. It emphasizes on the relationship between blade’s deformation energy and its curvature.Cantilever panels with different curvature radii are used to simulate blades to investigate the foreign objects damage characteristics of impacting on the convex sides and concave sides of blades with different curvature radii. And some rules on the effects of blade curvature on the characteristics of foreign objects damage are obtained.The energy balance model, elastic stress wave propagation and the fundamental hydrodynamics are respectively used to analyse the impact load for hard body, hyperelastic soft body and plastic soft body impacting on the blades.Hyperelastic soft body(rubber) and plastic soft body(gelatine) impacting on the rigid walls are analysed by numerical simulation. The two kinds of soft bodys impacting on the leading edges of blades are also simulated.The results suggest the two kinds of soft bodys are sliced by blades during impacting.And the impact damage for blade caused by rubber impacting is greater than the one caused by gelatine impacting under the same impacting conditions. With the same initial impacting energy and impacting angle, sandstone, rubber and gelatine,which are respectively considered as hard body, hyperelastic soft body and plastic soft body, are used to analyze foreign objects damage of blades. And rules for impacting characteristics of blades under different material objects impacting are gained. Modal analysis for blades before and after different material foreign objects damage is conducted through the method for explicit algorithmic switch to implicit algorithmic. The results indicate that natural frequencies of the blade are more influenced by the foreign objects damage,but the mode shapes are less influenced.Variety and the producing sequence of stress wave in the blade during impacted by foreign objects are investigated by using stress wave theory for Lamb’s problem.The possible damage to the blade caused by stress wave are also analyzed. Combined with numerical method, propagation and action characteristics of stress wave are researched.And the effects of impact load and strain rate on the propagation and action of stress wave are also analyzed.The results suggest that different impact load may lead to different crest values and wave lengths of incident wave in the blade. And the existing of strain rate increases the crest values of incident and reflected wave, decrease the attenuation velocity of stress wave.On the basis of theory of non-ideal impacting on the motion target in the terminal ballistics, an analysis model for foreign objects damage of blade with rotating motion is established to study the effects of blade’s rotating motion on the foreign objects damage of blade.Nonlinear dynamics model for FOD of blade with structural prestress is founded to analyze the effects of centrifugal prestress on the FOD of blade. And the dynamic relaxation method is used to obtain the initial stress and displacement field of blades in the beginning of the analysis of impacting.Combined with the theory for stress wave, numerical analysis for foreign objects damage of real blade with different rotating speeds is carried out.Then, rules for FOD of blade under different centrifugal loads are acquired.Finally,M20 bolt and rubber debris,which are respectively considered as hard body and soft body,are used to investigate the foreign objects damage of multi-blades with rotating speed.Differences of impacting characteristics between the two kinds of foreign objects are compared.更多还原