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。这给燃气轮机制造商带来了越来越大的压力，要求它们提高发动机效率，以保持产品的竞争力。提高燃气轮机效率的一种方法是提高涡轮入口温度(Tet)。现代发动机的TET高达2000K，远远高于制造第一级涡轮叶片的合金的熔点。采用了两种冷却技术来防止高TETS对叶片的损坏：气膜冷却，在叶片外表面引入一层薄薄的冷却剂以降低热传递的驱动温度；以及内部冷却，冷却剂通过叶片内的一系列通道来对流来自内表面的热量。用于冷却的空气是从压缩机中取出的，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%。研究气膜和内部冷却耦合的实验研究相对较少；因此，没有足够的公开数据来验证用于预测叶片金属温度的模型。这些预测几乎没有错误的余地：如果叶片运行的温度比预测的高出10K，那么它的寿命可能会减少一半。因此，叶片经常被过多地冷却，而牺牲了发动机的效率。经过验证的型号将使刀片冷却方案的设计更有信心。这将降低设计的保守性，使设计能够更有效地冷却设计，并相关地提高发动机效率。这也将降低重新设计或在使用中更换冷却不足的叶片的昂贵风险。拟议的项目将设计和建造一个高度模块化的试验台，以获得受膜和内冷却耦合作用的试件的流体动力学和热传递信息。该试验台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换热系数和温度，以及气膜冷却孔上方流体体积中的浓度场和三种成分的速度。该设施的灵活性与VFMS提供的无与伦比的测量技术保真度相结合，将使其成为研究薄膜-内部冷却组合的高度新颖和极其有用的平台。该项目的发现将为研究问题的基础科学提供独特的见解，并将为西门子-本提案中的工业合作伙伴-提供数据，以验证他们的模型和提供设计方法。这些数据还将提供给更广泛的燃气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.