An investigation into combined film and internal cooling of turbine blades

燃气轮机的主要用户正受到化石燃料价格上涨和政府严格的二氧化碳减排目标的影响。这给燃气涡轮机制造商带来了越来越大的压力，要求他们提高发动机效率，以使其产品保持竞争力。提高燃气涡轮机效率的一种方法是提高涡轮机入口温度（泰特）。当今发动机的TET高达2000 K，远高于制造第一级涡轮机叶片的合金的熔点。采用两种冷却技术来防止高Tclose对叶片的损坏：薄膜冷却，其中引入到叶片的外表面的冷却剂薄膜降低用于热传递的驱动温度;以及内部冷却，其中冷却剂通过叶片内的一系列通道以对流来自内表面的热量。用于这种冷却的空气从压缩机中取出，这对发动机效率是不利的：从压缩机中每抽出1%的空气，等熵效率就会下降1%。相对较少的实验研究已经调查了耦合膜和内部冷却，因此，有不足的公布的数据用于预测叶片金属温度的模型的验证。这些预测几乎没有误差：如果叶片工作的温度比预测的高10 K，叶片的寿命可能会减少一半。结果，叶片经常以发动机效率为代价被过度冷却。经过验证的模型将使叶片冷却方案的设计更有信心。这将减少设计保守性，从而实现更有效的冷却设计，并提高发动机效率。这也将减少重新设计或在服务中更换冷却不充分的叶片的昂贵风险。拟议的项目将设计和建造一个高度模块化的试验台，用于获得受耦合膜和内部冷却的试验件的流体动力学和传热信息。该装置将利用巴斯大学最先进的EPSRC资助的多功能流体测量系统（VFMS），能够高精度测量试件表面的传热系数和温度，以及薄膜冷却孔上方流体体积中的浓度场和三个分量速度。该设备的灵活性与VFMS提供的无与伦比的测量技术的保真度相结合，将使其成为研究组合膜内冷却的一个非常新颖和非常有用的平台。该项目的研究结果将为研究问题的基础科学提供独特的见解，并将为西门子-该提案的工业合作伙伴-数据来验证他们的模型并为设计方法提供信息。这些数据也将提供给更广泛的燃气涡轮机技术界和学术界的工作人员。

The primary users of gas turbines are being impacted by rising fossil fuel prices and stringent government targets for reducing carbon-dioxide emissions. This is putting increasing pressure on gas turbine manufacturers to improve engine efficiencies so that their products remain competitive. One way of improving the efficiency of a gas turbine is to raise the turbine entry temperature (TET). Present-day engines operate with TETs as high as 2000K, which is well above the melting point of the alloys from which first-stage turbine blades are made. Two cooling techniques are employed to prevent damage to the blades from high TETs: film cooling, where a thin film of coolant introduced to the external surface of the blade reduces the driving-temperature for heat transfer; and internal cooling, where coolant is passed through a series of passages within the blade to convect heat from the internal surfaces. The air for this cooling is taken from the compressor at a penalty to engine efficiency: for every 1% of air drawn from the compressor a 1% drop in isentropic efficiency follows. Relatively few experimental studies have investigated coupled film and internal cooling; consequently there are insufficient published data for validation of the models used to predict blade metal temperatures. There is little margin for error in these predictions: the life of a blade can be reduced by half if the temperature at which it operates is 10K higher than predicted. As a result, blades are often superfluously cooled at the expense of engine efficiency. Validated models would enable blade cooling schemes to be designed with more confidence. This would reduce design conservatism, enabling more efficiently cooled designs with an associated improvement in engine efficiency. It would also reduce the costly risk of re design or in-service replacement of inadequately cooled blades.The proposed project will design and build a highly-modular rig for obtaining fluid dynamic and heat transfer information on test pieces subjected to coupled film and internal cooling. The rig will make use of the University of Bath's state-of-the-art EPSRC funded Versatile Fluid Measurement System (VFMS), enabling high-precision measurements of heat transfer coefficients and temperatures on the surface of the test pieces, and the concentration field and three component velocities in the fluid volume above the film cooling holes. The flexibility of the facility combined with the unparalleled fidelity of measurement techniques offered through the VFMS will make it a highly novel and extremely useful platform for studying combined film-internal cooling.Findings from the project will provide unique insight into the fundamental science of the research problem and will supply Siemens - the industrial partner in this proposal - with data to validate their models and inform design methodology. The data will also be made available to workers in the wider gas turbine technical community and academia.