The effect of turbulence intensity on film cooling of gas turbine blade from trenched shaped holes

This paper reports a computational investigation on the effects of mainstream turbulence intensity on film cooling effectiveness from trenched holes over a symmetrical blade. Computational solutions of the steady, Reynolds-Averaged Navier–Stokes equations are obtained using a finite volume method with k − ε Turbulence model. Whenever possible, computational results are compared with experimental ones from data found in the open literature. Computational results are presented for a row of 25° forward-diffused film hole within transverse slot injected at 35° to AGTB symmetrical blade. Four blowing ratios, M = 0.3, 0.5, 0.9 and 1.3 are studied together with four mainstream turbulence intensities of Tu = 0.5, 2, 4 and 10%. Results indicate that the trenched shaped holes tend to give better film cooling effectiveness than that obtained from discrete shaped holes for all blowing ratios and all turbulence intensities. The trenching of shaped holes has changed the optimum blowing ratio and also the location of re-attachment of separated jet at high blowing ratios. Moreover, it has been found that the effect of mainstream turbulence intensity for trenched shaped holes is similar to that obtained for discrete shaped holes with the exception that the sensitivity of film cooling effectiveness to turbulence intensity has decreased for trenched shaped holes.     

含有非圆形双孔的无限平板中应力的解析解研究

无限平板中含有任意形状单个孔的问题可以使用复变函数方法获得其应力解析解.对于无限平板中含有两个圆孔或两个椭圆孔的双连通域问题,也可以利用多种方法进行求解,比如双极坐标法、应力函数法、复变函数法以及施瓦茨交替法等.其中复变函数中的保角变换方法是获得应力解析解的一个重要方法.但目前尚未见到用此方法求解无限板中含有一个正方形孔和一个椭圆孔的问题.当板在无穷远处受有均布载荷和孔边作用垂直均布压力时,利用保角变换方法可以求解板中含有两个特定形状孔的问题.该方法将所讨论的区域映射成象平面里的一个圆环,其中最关键的一步是找出相应的映射函数.基于黎曼映射定理,提出了该映射函数一般形式,并利用最优化方法,找到了该问题的具体映射函数,然后通过孔边应力边界条件建立了求解两个解析函数的基本方程,获得了该问题的应力解析解.运用ANSYS有限单元法与结果进行了对比.研究了孔距、椭圆形孔大小和两孔布置方位对边界切向应力的影响,以及不同载荷下两孔中心线上应力分布规律.      

Shape optimization of two equal holes in an infinite elastic plate

Abstract

The optimal design of the stress state in elastic plate structures with openings is a problem of great significance in engineering practice. Achieving proper shape of hole can reduce stress concentration around the boundaries remarkably. The optimal shape of a single hole in an infinite plate under uniform stresses has been obtained by complex variable method based on different optimal criteria. The complex variable method is particularly suitable for the hole shape optimization in infinite plate, in which the continuous hole boundary can be represented by the mapping function. It can also be used to solve the shape optimization problems of two or more holes. However, because of the difficulty of finding the mapping function for multi connected domain, the holes are mapped onto slits or separately mapped onto a circle. In this article, the two symmetrical and identical holes are mapped onto an annulus simultaneously by the newly found mapping function, which has a general form. The maximum tangential stress around the boundaries is minimized to achieve the optimal hole shape. And the coefficients of mapping function which describe the boundary are calculated by differential-evolution algorithm.     

自由面变化条件下隧道电子雷管爆破参数确定方法

电子雷管的技术潜力目前仍未在隧道工程中得以充分发挥,一个重要原因是没有严密理论支撑的爆破参数计算方法,药量、孔间延时等核心参数多沿用普通矿山法设计;其次是不能解决第二自由面形成后爆破参数计算准确性问题。以重庆观音桥隧道为研究背景,基于Anderson理论和电子雷管延时特性,提出隧道爆破在单自由面形成双自由面过程中,不同自由面条件下电子雷管爆破参数设计的新方法。现场获取不同药量单自由面单孔爆破振动曲线,逐一计算各孔间延时下的多孔合成振动,对比不同药量、不同延时合成振动曲线后确定单自由面爆破参数;根据电子雷管特点设计短延时掏槽爆破现场试验,获得起爆48 ms后已形成第二自由面;据此设计第二自由面形成后单孔爆破试验并计算双自由面下的合成振速、爆破参数,最终形成爆破全过程爆破参数计算方法。对计算结果进行综合分析后,现场设计主掏槽单孔药量1.2 kg,辅助掏槽单孔药量1.4 kg,孔间延时为5 ms;主掏槽与辅助掏槽间最小时差为35 ms;采用上述优化参数进行现场试验,在低振速控制的同时实现高效进尺。     

Film cooling effectiveness from trenched shaped and compound holes

This paper presents a comparative-numerical investigation on film cooling from a row of simple and compound-angle holes injected at 35° on a flat plate with four film cooling configurations: (1) cylindrical film hole; (2) 15° forward diffused film hole; (3) trenched cylindrical film hole; (4) trenched 15° forward-diffused film hole. All simulations are at fixed density ratio of 1.6, blowing ratio of 1.25, length-to-diameter L/D = 4 and pitch-to-diameter ratio of 3.0. The effect of length-to-diameter ratio on film cooling has been also investigated using L/D in the range of 1–8. Computational solutions of the steady, Reynolds-averaged Navier–Stokes equations have been obtained using a finite volume method. It has been found that the shape of the hole and the trenched holes can significantly affect the film cooling flow over the protected surface. Further, it has been shown that the film cooling effectiveness by trenched shaped holes is higher than all other configurations both in spanwise and streamwise specially downstream of the injection. Also, a trenched compound angle injection shaped hole produces much higher film cooling protection than the other configurations investigated in the present paper. The length-to-diameter ratio of trenched holes was found to have a significant effect on film cooling effectiveness and the spread of the coolant jets.     

基于均匀化理论的多孔板弯曲问题新解

由于密集型分布孔的存在,通常的有限元法不能有效地分析多孔板的弯曲问题.该文基于均匀化理论建立了该类问题的新解法.对含密集型分布的阶梯型圆孔板的分析结果,说明了该文方法是有效的.     

Hole-shape optimization in a finite plate in the presence of auxiliary holes

Minimizing the stress concentration around holes in uniaxially loaded finite plates is an important consideration in engineering design. One method for reducing the stress concentration around a central circular hole in a uniaxially loaded plate is to introduce smaller auxiliary holes on either side of the original hole to help smooth the flow of the tensile principal-stress trajectories past the original hole. This method has been demonstrated by Heywood and systematically studied by Erickson and Riley. Erickson and Riley show that for a central-hole diameter-to-plate width ratio of 0.222, the maximum stress reduction is up to 16 percent. In recent work, Durelliet al. show that the stress concentrations around holes in uniaxially loaded plates can be minimized by changing the hole shape itself till an optimum hole profile with constant stress values respectively on the tensile and compressive segments of the hole boundary is reached. By this technique the maximum stress reduction obtained for the above case is up to 20 percent. In the present work, starting with the optimum sizes and locations of central and auxiliary circular holes for a finite plate given by Erickson and Riley, a systematic study of the hole-shape optimization is undertaken. A two-dimensional photoelastic method is used. For a central-hole diameter-to-plate width ratio of 0.222, the reduction in stress-concentration factor obtained after hole-shape optimization is about 30 percent. It is also shown that it is possible to introduce the ‘equivalent ellipse’ concept for optimized holes.     

基于自适应泡泡法的薄壳结构拓扑优化设计

为有效解决薄壳结构拓扑优化设计难题,并满足其对分析模型精度和优化结果质量的高要求,结合等几何壳体分析方法提出一种基于自适应泡泡法的新型拓扑优化设计框架.等几何分析技术在薄壳分析方面具有天然的优势:一方面可为薄壳结构建立起精确的NURBS分析模型,避免了模型转换操作及误差;另一方面还可保证待分析物理场的高阶连续性,无需设置转角自由度等.为了在给定壳面上实现结构的拓扑演化,借助NURBS曲面(即等几何分析中的薄壳中面)的映射关系,仅需在规则的二维参数区域内改变结构拓扑即可.鉴于此,采用自适应泡泡法在壳面参数区域内开展拓扑优化,该方法包含孔洞建模、孔洞引入和固定网格分析3个模块,其在当前工作中分别基于闭合B样条、拓扑导数理论和有限胞元法实现.其中,闭合B样条兼具参数和隐式两种表达形式,参数形式便于在CAD系统中直接生成精确的结构模型;隐式形式不仅便于开展孔洞的融合/分离操作,还能与有限胞元法有机结合以替代繁琐的修剪曲面分析方法.理论分析和数值算例表明,所提优化设计框架将复杂的薄壳结构拓扑优化问题转化为简单的二维结构拓扑优化问题,在保证足够分析精度的基础上使用相对很少的设计变量就可得到具有清晰...     

基于声学超材料的穿孔板缺陷态俘能特性研究

论文提出了一套适用于在低频段区间工作的声学超材料俘能装置.通过在含孔的声学超材料结构中制造一个局域共振缺陷态,进而将入射声波的弹性应变能集中在缺陷区域中,并利用压电晶片实现能量的转化.论文采用有限元的方法研究了元胞含孔的声学超材料在共振频率下俘获功率与电压的性能.进一步地,通过逐渐改变孔的尺寸,探究了孔径大小对俘能效果的影响.数值计算结果表明:相比于元胞不含孔的声学超材料俘能装置,通过在元胞上打孔可以明显地提高装置在低频段的俘能特性.论文提出的装置具有易加工,实用性强等优点,进一步提高了其在低频区间俘能的工作能力,具有潜在的应用前景.     

动载荷下含空气泡的TNT装药安全性能的实验研究

本文采用自行设计加工的应力发生器装置,对被试验炸药施加上升时间为1030ms的压力加载;应用数理统计的方法(试验设计的正交法和感度试验的上下法),实验研究了含有各种空气泡的压装TNT在此压力加载下的安全性规律,并由此外推得到了不含空气泡的压装TNT在此压力加载下的安全性能。     

考虑嵌入移动孔洞的多相材料布局优化

工程结构设计问题中经常需要预先嵌入一个或多个固定形状的孔洞以满足某些功能性或者制造性设计要求.为了有效求解这种带有嵌入可移动孔洞的多相材料连续体结构布局优化问题,通常需要同时优化这些嵌入孔洞的位置和方向及多相材料结构的拓扑构型,以改善结构的整体性能.为此,本文采用参数化的水平集函数描述嵌入孔洞的几何形状,并将定义多相材料结构拓扑的材料密度以及描述嵌入孔洞的位置和方向的几何参数视为所考虑优化问题的设计变量.为了避免由于孔洞移动造成的重新划分网格的繁琐及改善计算效率,使用平滑化的Heaviside函数将所有嵌入孔洞映射为固定网格上的密度场.同时,提出了一种在有限元水平上调用的类SIMP材料插值格式,用于优化问题的材料参数化,进而实现多相材料结构拓扑构型和嵌入孔洞位置和方向的同步优化.这种材料插值格式便于几何变量的解析灵敏度分析,使得当前的优化问题可以用基于梯度的优化算法求解.优化算例证明所提方法可以有效地处理带有多个嵌入孔洞的多相材料结构布局优化问题.      

缝合复合材料层板刚度预报

提出了缝合复合材料层板的刚度预报模型,该模型考虑了缝合针脚处的孔洞对刚度的影响,描述了缝合孔洞的几何形态,建立了孔洞形态与纤维弯曲的关系,采用平均刚度法和经典层合板理论进行了刚度预报,获得了与试验数据相吻合的预报结果,表明了该模型的有效性,详细探讨了缝合孔洞对缝合层板刚度的影响规律,得到一些有益结论。     

FATIGUE LIFE PREDICTION OF SUS 630 （H900） STEEL UNDER HIGH CYCLE LOADING

The fatigue life prediction of high strength steel SUS 630 （H900） under high cycle loading is conducted with consideration of a characteristic fatigue length of material. Based on the WShler curve of smooth materials, a modified method for fatigue life prediction is approached. The characteristic fatigue length of material under cyclic loading is associated with the polycrystalline material. Rather than the stress at a point, the average stress within the characteristic fatigue length is implemented for the fatigue life prediction. The method can be applied to both the smooth and the defected material. The fatigue life prediction is also verified experimentally by specimens with various small circular holes. Through the comparison, it is found that the method can be adopted to predict the fatigue lives with different size effects.     

具有内部特征约束的四边形网格生成方法

提出一种具有内部特征约束的四边形网格自动生成方法,可以处理内部具有孔洞、约束线、约束点以及密度线、密度点等特征约束,满足数值分析中对网格生成的特殊要求。以区域分解法为基础,提出了确定最佳切割线的方法以及在切割线上生成过渡均匀网格节点的方法;将约束线、约束点以及密度线、密度点作为面积为零的孔洞,提出了对特征约束的处理方法;针对特征约束分隔区域的情况,提出了自动确定各子区域边界的方法。基于本文提出的方法已开发出具有特征约束的四边形网格自动生成程序,并成功应用于洪水分析系统和楼面设计分析系统。     

局部正交无网格伽辽金法的研究及其在含多裂纹多孔结构中的应用

通过对无网格法中正交基函数的研究,提出局部正交无网格伽辽金法,局部正交基函数保持原正交基函数的性质,但其导数具有了通式,简洁明了,易于编程实现,计算效率高,并将其应用到求解含多裂纹多孔均匀拉伸板的应力强度因子中,计算结果与用正交无网格伽辽金法和有限元法得到的结果进行比较,证明了局部正交无网格伽辽金法的可行性和正确性。     

深孔控制卸压爆破机理和防突试验研究

针对当前各种局部防突措施的优缺点和局限性,对兼有松动爆破与大直径卸压钻孔爆破两种措施优点的局部防突措施—深孔控制卸压爆破进行了研究。在理论上和利用实验室模型实验对深孔控制卸压爆破中的控制孔的作用进行了研究分析。深孔控制卸压爆破的现场防突试验表明:该法效果明显、工艺简单、经济效益好、安全且适应性强,是一种易于推广的局部防突措施,有着广阔的应用前景。     

含孔平板弹性波散射问题的复变函数方法

本文采用平板弯曲波动理论及复变函数方法，对平板开孔弹性波的散射及动应力集中问题进行了分析研究，得到了传播急剧记波时此种平板弯曲波动问题的分析解。若同时采用保角射技术，就为主解平板任意形状开孔弹性波的散射及动应力集中问题提供了一种统一规范的方法。作为算例，本文给出了平板开圆孔和椭圆孔附近的动应力集中系数的数值结果，并对其进行了讨论。     

Surface finish of open holes on fatigue life

In this paper, the effect of surface finish of open holes on the fatigue life has been studied. Four defects of the surface finish are simulated. They are scratch, void, inclusion and roundness. Firstly, the effect of the four defects on the stress distributions around the holes has been studied by the finite element method (FEM). The fatigue lives are determined based on the stress distributions by the method of nominal stress approach. The results show that the fatigue lives are dependent on the quantity of the surface finished. There are the critical defect values of scratch, void and inclusion, smaller than which there is no effect of the surface finish on the fatigue life. For these three defects, the fatigue lives decrease with the increasing of the values of the defects. It is the same to the defect of roundness, e.g. the bigger roundness tolerance is, the shorter the life is. Further, an approximate quadratic curve has been found for the relationship between the roundness tolerances and their logarithmic fatigue lives.     

Homogenization-based method for bending analysis of perforated plate

Owing to the existence of distributed holes, it is difficult to solve the bending problem of perforated plates by the conventional finite element method. A homogenization-based method for this problem is presented in this paper. As an example, the bending analysis of a circular perforated plate with distributed step-wise cylindrical holes is made. The deflection and the fundamental frequency obtained by present method are in good agreement with experimental data, this implies that the method is effective. This project is supported by the National Natural Science Foundation (19602007) and National Outstanding Youth Foundation (19525206).     

Scattering of flexural wave in a thin plate with multiple circular holes by using the multipole Trefftz method

The scattering of flexural wave by multiple circular holes in an infinite thin plate is analytically solved by using the multipole Trefftz method. The dynamic moment concentration factor (DMCF) along the edge of circular holes is determined. Based on the addition theorem, the solution of the field represented by multiple coordinate systems centered at each circle can be transformed into one coordinate system centered at one circle, where the boundary conditions are given. In this way, a coupled infinite system of simultaneous linear algebraic equations is derived as an analytical model for the scattering of flexural wave by multiple holes in an infinite plate subject to the incident flexural wave. The formulation is general and is easily applicable to dealing with the problem containing multiple circular holes. Although the number of hole is not limited in our proposed method, the numerical results of an infinite plate with three circular holes are presented in the truncated finite system. The effects of both incident wave number and the central distance among circular holes on the DMCF are investigated. Numerical results show that the DMCF of three holes is larger than that of one, when the space among holes is small and meanwhile the specified direction of incident wave is subjected to the plate.