斜孔气膜冷却数值模拟分析

本文通过数值模拟分析圆柱孔和扩散孔的单斜孔气膜冷却特性,考察复合角、孔型和吹风比对流场和气膜冷却效果的影响。结果表明,复合角的引入使气膜侧向分布更宽,但冷却效果沿主流方向衰减更快。适中吹风比得到的气膜能更有效的保护壁面。在相同吹风比和复合角条件下,扩散孔的气膜冷却效率比圆柱孔更好,且冷却更为均匀持久。     

湍流黏性修正在不同孔型气膜计算中的应用

燃气轮机气膜冷却流动中的复杂涡系使得其湍流黏性系数体现出很强的各向异性。本文采用作者提出的代数各向异性湍流黏性系数修正方法(AAEV方法),对不同孔型气膜冷却进行了研究。文中结合平板圆孔、扇形孔气膜冷却实验结果,将传统的湍流模型与修正后的湍流模型获得的模拟结果与实验值进行了比较,得到修正后的结果与实验有较好的吻合度。修正后的湍流模型对不同的孔型有很好的适用性,同时揭示了两种孔不同的三维特性。     

新型双射流冷却孔对气膜冷却效率影响的研究

气膜冷却是现代航空燃气轮机涡轮冷却技术的一种重要方法,冷却孔形状的改进是提高气膜冷却效率的重要手段。本文对双射流冷却孔形状进行了改型,并对新型双射流冷却孔在吹风比分别为0．5,1．0,1．5,2．0时的冷却效率进行了数值模拟。模拟结果表明新型双射流冷却孔与原双射流冷却孔相比在各吹风比下均优化了气膜在热表面上的分布,抑制...     

复合冲击和复合旋流冷却特性的对比研究

针对应用旋流冷却和气膜冷却对涡轮叶片前缘区进行冷却系统设计的科学命题,首次建立了包含冷气腔、冲击/旋流腔、气膜孔和燃气主流通道的复合冲击和复合旋流冷却模型,利用数值方法在相同几何和气动条件下对比了复合冲击和复合旋流冷却的流动换热特性.研究结果表明:冲击孔/旋流喷嘴流量沿X方向逐渐增大,吹风比沿X方向先增大后减小.复合冲击冷却的气膜孔流量和吹风比沿X方向略有增大,复合旋流冷却气膜孔流量和吹风比沿X方向减小.复合旋流冷却平均Nu比复合冲击冷却提升13.0%.气膜孔会扰动冷气流动,使附近小范围区域Nu提升.与复合冲击冷却相比,复合旋流冷却气膜孔的冷气流量和速度大,肾型对涡强度高,绝热气膜冷却效率减小.     

不同吹风比下平面叶栅气膜冷却数值模拟

本文对具有多排冷却孔的某叶栅进行了气膜冷却数值模拟,计算了三种湍流模型在不同吹风比下叶片表面的气膜冷却效率。将数值计算结果与采用压力敏感漆实验技术测量的叶片表面气膜冷却效率分布进行了对比,比较了不同湍流模型的预测准确性,并验证了数值计算对平面叶栅气膜冷却定性预测的可行性。     

带肋通道和气膜冷却交互下的绝热和耦合传热研究

燃气轮机透平叶片冷却中,内部肋片扰流对气膜冷却效果有显著影响,当边界条件为金属壁面绝热和金属壁面耦合时,冷却效率会有不同的表现。本文采用数值计算方法,分别计算绝热边界和耦合边界条件下,气膜孔进口与内部冷却扰流肋片不同相对位置条件下的绝热气膜冷却效率和耦合条件下的整体冷却效率进行计算。结果表明当气膜进口位于肋后扰流区时,绝热气膜冷却效率较差。绝热边界和耦合边界条件下流场相似,气膜孔与肋片相对位置对于气膜孔下游整体冷却效率的影响与绝热条件相似。     

气膜和冲击复合冷却结构耦合传热数值研究

本文采用数值方法研究了气膜和冲击复合冷却结构的耦合传热和综合冷效。复合冷却平板模型布置有两个交错气膜孔和若干排冲击孔,气膜孔和冲击孔均采用圆柱孔型。分别研究了吹风比和冷气量分配对综合冷效、流场结构和对流换热特性等的影响规律,结果表明:复合冷却综合冷效明显受到吹风比影响;适当调节冷气量的分配,能够明显提高综合冷效。     

定出流面积条件下气膜冷却孔型的研究

本文采用数值模拟的方法,在保持冷却射流出口面积不变的条件下,分析比较了圆柱形孔、扇形孔、双射流孔和带双肩形孔这几种气膜孔的冷却效果。研究结果表明:对于圆柱形孔,气膜冷却效率在吹风比M=0.5左右效率较高;对于扇形孔,在对应圆柱形孔吹风比M=1.5时的效率要优于低吹风比情况;对于双射流孔和带双肩形孔,在对应圆柱形孔吹风比M=1.0时的冷却效果更好。原因在于高吹风比情况下,圆柱形孔结构中冷却射流与高温主流形成较强的肾形涡,会使冷却气体脱离壁面,并将高温主流卷入冷却气膜层,从而破坏冷却效果,而扇形孔、双射流孔以及带双肩形孔能有效地抑制肾形涡对冷却流的提升作用,从而保持冷却气膜的贴壁性,提高了气膜冷却效率。     

涡轮叶顶冷却布置对叶顶传热冷却性能的影响

本文采用数值模拟的方法,对比分析了1+1/2对转涡轮四种不同的叶顶冷却布置方案对叶顶传热、冷却性能以及气动特性的影响。四种布置方案分别是:靠近压力面垂直叶顶方向、靠近压力面且与叶顶有30°出射角、中弧线位置垂直叶顶方向、中弧线位置有30°出射角。研究表明,气膜孔沿压力面布置与气膜孔沿中弧线布置相比可以降低叶顶传热系数;由于气膜孔倾斜布置气膜射流动量降低,且削弱了肾形涡的影响,气膜的侧向覆盖范围增大。因此气膜孔靠近压力面布置可以提高气膜冷却效率;气膜孔靠近压力面且有30°出射角比垂直布置叶顶热负荷减少2.7%。另外,气膜孔靠近压力面布置可以降低主流的泄漏流量,有利于减小泄漏损失和提高涡轮效率。     

气膜孔内流动结构对冷却效率的影响

涡轮叶片气膜孔内的流场结构对气膜射流下游的流动有着明显的影响。本文应用数值模拟的方法计算了平板上四种气膜冷却结构的孔内涡流场,从而分析气膜孔内涡结构对气膜冷却效率的作用规律。结果表明:当射流进入气膜孔并发生偏转时,气膜孔内会生成不同强度的旋转涡对;此对涡会导致气膜孔内射流能量的损失,并对主流内的肾型涡产生作用。当孔内涡对与主流肾型涡转向相同时,主流肾型涡湍流强度增加,气膜冷却效率下降;反之,当孔内涡转向与主流肾型涡相反时,主流肾型涡湍流强度降低,气膜冷却效率提升。通过对孔内涡结构的优化,文中所提的两种气膜孔改型结构能够有效地提高气膜冷却效率。     

气膜孔角度对动叶前缘冲击/气膜复合冷却的影响

本文针对GE-E3第一级动叶前缘的冲击/气膜复合冷却结构进行了热流耦合数值研究.采用标准k-ω湍流模型,分析了前缘气膜孔对称布置时,其角度对透平动叶前缘冲击/气膜复合冷却特性的影响;在五种冷气质量流量比(MFR=0005,0.010, 0.016, 0.020, 0.025)下,研究了气膜孔在不同角度(β=20°,25...     

Effect of impingement jet on the full-coverage film cooling system with double layered wall

The present study was conducted to evaluate the total cooling effectiveness in combined full-coverage film cooling and impingement jet using an infrared thermographic technique. The effect of film cooling hole angle, blowing ratio, and height to diameter ratio between the film cooling and impingement jet plates was discussed. The total cooling effectiveness increased as impingement jet cooling was added. The angled film cooling holes had approximately 4.6% higher total cooling effectiveness than the normal film cooling holes. The total cooling effectiveness was almost constant regardless of height to diameter ratio, but enhanced as the blowing ratio was increased.     

Interaction Mechanism and Loss Analysis of Mixing between Film Cooling Jet and Passage Vortex

The interaction between the film-cooling jet and vortex structures in the turbine passage plays an important role in the endwall cooling design. In this study, a simplified topology of a blunt body with a half-cylinder is introduced to simulate the formation of the leading-edge horseshoe vortex, where similarity compared with that in the turbine cascade is satisfied. The shaped cooling hole is located in the passage. With this specially designed model, the interaction mechanism between the cooling jet and the passage vortex can therefore be separated from the crossflow and the pressure gradient, which also affect the cooling jet. The loss-analysis method based on the entropy generation rate is introduced, which locates where losses of the cooling capacity occur and reveals the underlying mechanism during the mixing process. Results show that the cooling performance is sensitive to the hole location. The injection/passage vortex interaction can help enhance the coolant lateral coverage, thus improving the cooling performance when the hole is located at the downwash region. The coolant is able to conserve its structure in that, during the interaction process, the kidney vortex with the positive rotating direction can survive with the negative-rotating passage vortex, and the mixture is suppressed. However, the larger-scale passage vortex eats the negative leg of the kidney vortices when the cooling hole is at the upwash region. As a result, the coolant is fully entrained into the main flow. Changes in the blowing ratio alter the overall cooling effectiveness but have a negligible effect on the interaction mechanism. The optimum blowing ratio increases when the hole is located at the downwash region.     

瞬态液晶技术在涡轮叶片内部冷却研究中的应用

瞬态液晶测量技术能有效测量物体表面的换热系数,目前已经在传热研究中得到了广泛的应用。本文重点介绍了该测量方法在高温涡轮叶片内部冷却传热研究中的实验过程及应用。对内部冷却U型通道的传热研究表明:气膜抽吸作用下,通道内孔附近的传热得到强化,但区域平均传热系数变化不大;同时抽吸能使带肋通道中的压力损失有所降低。为了满足叶片冷却设计中对传热和压力损失的不同要求,改变弯头区的结构形式是一种有效的手段。实验结果进一步表明,瞬态液晶测量方法能准确地测量内部冷却通道中的传热分布,能为测量和优化涡轮叶片内部冷却传热特性提供可靠的数据支持。     

A numerical study of rotation effects on jets effusing from inclined holes into a cross-flow

In this work, the complexity of the flow field arising from the impact of the interaction of coolant jets with a hot cross-flow under rotation conditions was numerically simulated using large eddy simulation with artificial inflow boundary condition. The finite-volume method and the unsteady PISO (Pressure Implicit with Splitting of Operators) algorithm were applied on a non-uniform staggered grid. The simulations were performed for four different values of rotation number (Ro) of 0.0, 0.03021, 0.06042, and 0.12084, a jet Reynolds number of 4700, based on the hole width and the jet exit velocity. The air jet was injected at 30° and 90° in the streamwise direction with a density ratio of 1.04 and a velocity ratio of 0.5. The flow fields of the present study were compared with experimental data in order to validate the reliability of the LES technique. It was shown that the rotation has a strong impact on the jet trajectory behaviour and the film cooling effectiveness. The film trajectory always inclines centrifugally. Under rotating conditions, the film trajectory departs from the centreline to the left boundary. The deflection becomes greater as Ro increases. Furthermore, it was also found that the injection angle has a strong impact on separation and reattachment behaviour as well as the strength of the penetration into the cross-flow. As it increases, the distribution of the film cooling downstream the jet exit is more non-uniform and the film cooling effectiveness level slightly decreases.     

湍流度对单排圆孔及后扩孔气膜冷却的影响

通过传热-传质类比法研究了湍流度对单排圆柱孔及后扩孔气膜冷却效率的影响.计算结果表明,小吹风比M=0.5时,圆柱孔与后扩孔的壁面冷却效率相当,湍流度趋向于在整个下游区域使冷却效果恶化;大吹风比M=2时,后扩孔产生的壁面气膜冷却效率的提高明显,而湍流度的提高强化了冷却剂向壁面的扩散,削弱了冷却气膜脱离壁面的现象,趋向于在整个下游区域提升冷却效率.     

Shape optimization of multi-chamber cross-flow mufflers by SA optimization

It is essential when searching for an efficient acoustical mechanism to have an optimally shaped muffler designed specially for the constrained space found in today's plants. Because the research work of optimally shaped straight silencers in conjunction with multi-chamber cross-flow perforated ducts is rarely addressed, this paper will not only analyze the sound transmission loss (STL) of three kinds of cross-flow perforated mufflers but also will analyze the optimal design shape within a limited space.In this paper, the four-pole system matrix used in evaluating acoustic performance is derived by using the decoupled numerical method. Moreover, a simulated annealing (SA) algorithm, a robust scheme in searching for the global optimum by imitating the softening process of metal, has been adopted during shape optimization. To reassure SA's correctness, the STL's maximization of three kinds of muffles with respect to one-tone and dual-tone noise is exemplified. Furthermore, the optimization of mufflers with respect to an octave-band fan noise by the simulated algorithm has been introduced and fully discussed. Before the SA operation can be carried out, an accuracy check of the mathematical model with respect to cross-flow perforated mufflers has to be performed by Munjal's analytical data and experimental data.The optimal result in eliminating broadband noise reveals that the cross-flow perforated muffler with more chambers is far superior at noise reduction than a muffler with fewer chambers. Consequently, the approach used for the optimal design of noise elimination proposed in this study is certainly easy and efficient.     

光学薄膜自动设计的多目标优化方法

光学薄膜中已使用的优化方法郜是单目标寻优的,通过分析光学薄膜优化设计的原理,将薄膜设计的物理问题归结为混合离散变量的多目标优化设计的数学模型,并认为这是薄膜设计的一般性模型,现行的单目标优化算法只是这个模型的简化.基于这一新思路,并结合多目标优化算法的研究现状,采用了一种基于免疫应答原理的智能型多目标优化算法.该算法隐含并行处理能力,原理上是具备全局搜索能力的自适应随机性算法.将此算法运用到光学薄膜设计中,给出了一些优化的设计实例.结果表明,将多目标优化算法引入薄膜设计的新思路是可行的,将来会有较好的发展前景.     

叶顶单一气膜孔位置传热特性的数值研究

本文采用数值模拟的方法对凹槽叶顶前缘气膜孔的位置进行了研究,通过改变前缘第一气膜孔位置来分析叶顶区传热。数值模拟结果表明,由于冷却气对该区域没有提供足够的保护,肩壁表面的平均绝热效率远低于凹槽底面,平均传热系数远高于凹槽底面。叶顶第一气膜孔向前缘移动使肩壁表面的平均传热系数先升高再降低,叶顶前缘低绝热冷却效率区逐渐消失...