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A robust conjugate heat transfer methodology with novel turbulence modeling applied to internally-cooled gas turbine airfoils.

机译：一种稳健的共轭传热方法，具有适用于内部冷却燃气轮机翼型的新型湍流模型。

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摘要

Computational fluid dynamics and heat transfer (CFD) has become a viable, physics-based analysis tool for complex flow and/or heat transfer problems in recent years due, in large part, to rapid advances in computing power. CFD based on the Reynolds-averaged Navier-Stokes (RANS) equations is starting to enter the mainstream design environment in certain industries where rapid and reliable predictive capability is necessary. One such application is the gas turbine industry, where thermal management of airfoils at extremely high temperatures is one of the most critical components in engine design for reliability. The problem is complicated by the need for advanced airfoil cooling techniques, which typically includes internal convection cooling.; Current turbine aerothermal design practice involves separate simulations or empirical correlations for the airfoil external aerodynamics and heat transfer, the internal heat transfer, and conduction in the metal part. This approach is time-consuming and quite inefficient when design iterations are required, and accuracy is lost in the decoupling of the heat transfer modes. The physically-realistic approach is a single CFD simulation in which the convective heat transfer (fluid zones) and heat diffusion in the solid are fully coupled. This is known as the conjugate heat transfer (CHT) method, and it is ideally suited to the rigors of design. An obstacle to the adoption of the CHT method is difficulty in the accurate prediction of heat transfer coefficients on both external and internal surfaces, which is usually attributed to performance of the turbulence models used to close the RANS equations.; The present study develops a comprehensive, "best-practice" RANS-based conjugate heat transfer methodology for application to the aerothermal problem of an internally-cooled gas turbine airfoil at realistic operating conditions. With the design environment in mind, attention is given to high-quality mesh generation, efficient solution initialization, and solution-based adaption for grid-independence. Matching the conditions of the only experimental test case available in the literature, the simulations consist of a linear cascade of C3X vanes cooled by air flowing radially through ten smooth-walled cooling channels. Initially, popular "off-the-shelf" k-epsilon turbulence models are employed. Predictions for vane external surface temperature distribution at the midspan generally agree well with experimental data. The only exception is along a portion of the suction (convex) surface of the airfoil, where the predicted temperature is significantly greater than measured. This indicates an overprediction in the local heat transfer coefficient, and it corresponds to the region of strong curvature of the surface.; In an effort to correct the excessive heat transfer coefficients predicted on the vane suction surface, a new eddy-viscosity-based turbulence model is developed to include correct sensitivity to the effects of streamline curvature (and, by analogy, system rotation). The novel feature of the model is the elimination of second derivatives in the formulation of the eddy-viscosity, making it much more robust than other curvature-sensitive models when implemented in general-purpose solvers with unstructured meshes. A new dynamic two-layer near-wall treatment is included for integration of the flow to the wall. The new model is proven to exhibit physically-accurate results in several fundamental test cases. When the C3X vane conjugate heat transfer simulation is revisited with the new model, the heat transfer coefficients in the region of strong convex iv curvature are correctly attenuated, and the wall temperature predictions are much closer to measurements.; Cooling channels in many hot-section turbine airfoils have ribs machined on their walls to augment heat transfer, and they make multiple passes through the airfoil, meaning sharp turns are present. In order to extend the CHT methodology to the
机译：近年来，计算流体动力学和热传递（CFD）已成为一种可行的基于物理的分析工具，用于解决复杂的流动和/或热传递问题，这在很大程度上是由于计算能力的飞速发展。基于雷诺平均Navier-Stokes（RANS）方程的CFD开始进入某些需要快速而可靠的预测能力的行业的主流设计环境。燃气轮机行业就是这样的一种应用，其中在极高的温度下对翼型进行热管理是确保可靠性的发动机设计中最关键的组件之一。需要先进的机翼冷却技术使问题变得复杂，该技术通常包括内部对流冷却。当前的涡轮机空气热设计实践涉及翼型外部空气动力学和热传递，内部热传递以及金属零件中的传导的单独的模拟或经验相关性。当需要进行设计迭代时，这种方法既耗时又效率低下，并且在传热模式的去耦中失去了精度。物理逼真的方法是单个CFD模拟，其中对流传热（流体区域）和固体中的热扩散完全耦合。这称为共轭传热（CHT）方法，非常适合严格的设计。采用CHT方法的一个障碍是难以准确预测内外表面的传热系数，这通常归因于用于关闭RANS方程的湍流模型的性能。本研究开发了一种综合的，“最佳实践”的基于RANS的共轭传热方法，用于在实际运行条件下应用到内部冷却的燃气轮机翼型的空气热问题。考虑到设计环境，我们将注意力集中在高质量网格生成，有效的解决方案初始化以及基于解决方案的网格独立适应性上。匹配文献中唯一的实验测试用例的条件，模拟包括线性C3X叶片级联，这些叶片由径向流经十个光滑壁冷却通道的空气冷却。最初，使用流行的“现成”k-ε湍流模型。中跨叶片外表面温度分布的预测与实验数据基本吻合。唯一的例外是沿着机翼的吸力（凸面）表面的一部分，该处的预测温度明显高于实测温度。这表明对局部传热系数的预测过高，并且它对应于表面的强曲率区域。为了纠正在叶片吸入表面上预测的过多的传热系数，开发了一种新的基于涡流粘度的湍流模型，以包括对流线曲率影响的正确敏感性（以此类推，对系统旋转也是如此）。该模型的新颖之处在于消除了涡流粘度公式中的二阶导数，使其在具有非结构化网格的通用求解器中实现时，比其他曲率敏感模型更加健壮。包括新的动态两层近壁处理，可将流整合到壁上。事实证明，新模型在几个基本测试案例中均能显示出精确的物理结果。当使用新模型重新考虑C3X叶片共轭传热模拟时，在强凸iv曲率区域内的传热系数将被正确衰减，并且壁温的预测值将更接近于测量值。许多热切面涡​​轮机翼型的冷却通道的壁上都加工有肋条，以增加热量传递，并且使翼型多次通过翼型，这意味着存在急转弯。为了将CHT方法学扩展到

著录项

  • 作者

    York, William David.;

  • 作者单位

    Clemson University.;

  • 授予单位 Clemson University.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2006
  • 页码 224 p.
  • 总页数 224
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

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