CFD investigations of turbine rim seal physics

这个博士研究项目涉及牛津大学和劳斯莱斯ICORE项目的合作，主要目的是提高对轴向涡轮轮辋密封相关的流体动力学现象的理解。这在航空发动机和发电用燃气轮机的设计中很重要。特别是，设计人员希望以最小的计算成本准确地预测边缘密封空腔现象对涡轮气动扰流和传热的影响。在过去的几十年里，计算流体动力学（CFD）模型的应用与实验相比，结果喜忧参半。在某些情况下，CFD和测量之间已经证明了良好的定性和/或令人鼓舞的定量一致性。在一些测试用例的研究中，发现实验数据与数值数据明显不匹配。这通常归因于建模错误，但应该指出，实验不确定性也可能是一个重要因素。这在最近发表的实验工作中得到了证实。最近发表的计算和实验工作也证实了边缘密封腔的流动是由复杂的物理和混合流动现象所控制的，这对目前工业上的理解和设计方法提出了挑战。在本研究项目的第一部分，将通过URANS模拟对三种不同配置（无叶片和叶片的动-静系统、带叶片的动-静系统和带叶片和叶片的动-静系统）的主环空流动效应进行系统评估。特别关注非定常的敏感性和密封有效性的主环空和内腔流动条件，轴向和环空间隙将给出。通过求解被动标量浓度方程，采用物种浓度来估计密封效果，并考虑密封类型的影响。将与牛津大学的测量结果进行比较。由于大规模模拟的计算费用，以前没有尝试过这种系统的研究。该结果将直接引起劳斯莱斯工程师的兴趣，并与免费的实验计划相结合，将进一步阐明CFD模型的优缺点。研究的第二部分可能取决于最初研究和实验计划的结果。例如，可能需要进一步的CFD研究来研究可能导致与实验不同的实验因素（如转子偏心），或者研究设计中特别感兴趣的几何变化。为了研究建模效果，将考虑更多的计算要求技术，如大涡流模拟，并与热流体系统大学技术中心的其他研究人员合作开发。

This PhD research project , involving collaborations with the University of Oxford and the Rolls-Royce ICORE program, has the main aim to improve understanding of fluid-dynamic phenomena associated with the sealing of axial turbine rims. This is important in the design of gas turbines for aeroengines and power generation. In particular, designers would like to accurately predict the effects of rim seal cavity phenomena on turbine aerodynamic spoiling and heat transfer at minimum computational cost. The employment in the last decades of computational fluid dynamics (CFD) models has shown mixed results when compared to experiments. In some cases good qualitative and/or encouraging quantitative agreement between CFD and measurement has been demonstrated. In studies of some test cases a clear mismatch between experimental and numerical data has been identified. This is often attributed to modeling errors but it should be noted that experimental uncertainties may also be a strong factor. This has been confirmed in recently published experimental work. Recent publications of both computational and experimental work also confirm that rim seal cavity flows are ruled by complex physics and mixed flow phenomena, challenging current understanding and design methods in industry. In the first part of this research project, a systematic assessment of the main annulus flow effect through URANS simulations for three different configurations (rotor-stator system without blades and vanes, rotor-stator system with vanes and rotor-stator system with blades and vanes) will be carried out. A particular focus on sensitivity of the unsteadiness and the sealing effectiveness to the main annulus and inner cavity flow conditions, axial and annulus gap will be given. Species concentrations through the solution of a passive scalar concentration equation will be employed for the estimation of the sealing effectiveness and the effect of seal type will also be considered. Comparison will be made to measurements taken at the University of Oxford. Owing to the computational expense of large scale simulations no such systematic study has previously been attempted. The results will be of direct interest to Rolls-Royce engineers and in combination with the complimentary experimental programme will further clarify the strengths and weakness of CFD models. The second part of the research may depend on the outcomes of the initial study and experimental programme. For example further CFD studies may be required to investigate experimental factors (such as rotor eccentricity) that could lead to differences with experiments, or to investigate geometrical changes that would be of particular interest in design. To investigate modeling effects, more computationally demanding techniques, such as large-eddy-simulation will be considered and developed in collaboration with other researchers in the Thermo-Fluid Systems University Technology Centre.