The performance evaluation for thermal protection of turbine vane with film cooling and thermal barrier coating

Abstract

• An expression of temperature-independent overall cooling effectiveness is obtained. • The external convective heat transfer is effected by the internal cooling flow. • Increasing convective heat transfer can increase overall cooling effectiveness. • Four parameters need to be similar when conducting heat transfer experiments. When conducting wind tunnel heat transfer test to evaluate the cooling performance of the turbine, it is difficult and costly to simulate the extremely high temperature gas of the real working conditions, and small temperature difference and room temperature test is usually used instead. In order to evaluate the cooling performance under real working conditions from the experimental results at room temperature, the corresponding evaluation method needs to be studied. In this paper, a turbine vane with film cooling and thermal barrier coating (TBC) is used as the study object. By introducing an improved driving temperature and adopting one-dimensional heat transfer analysis, an improved analytical expression of overall cooling effectiveness, which is independent of temperature, is derived and analyzed. Through numerical calculation, the overall cooling effectiveness defined by different reference temperatures are compared. The results show that the heat transfer of the turbine vane with film cooling and TBC is complicated. The influence of the internal cooling should be considered when calculating the external convective heat transfer. The temperature-independent overall cooling effectiveness on the TBC surface and the superalloy surface are obtained, respectively. The improved overall cooling effectiveness is more sensitive to the thermal resistance of the superalloy compared with the thermal resistance of the TBC. The overall cooling effectiveness can be improved by increasing the internal or external convective heat transfer coefficient. In order to obtain an accurate overall cooling effectiveness (dimensionless wall temperatures), it is necessary to satisfy similarities of four dimensionless parameters, including the Biot numbers ( B i TBC , B i w ), the ratio of external and internal convective heat transfer coefficients ( h e / h i ) and the ratio of gained convective heat transfer coefficient and external convective heat transfer coefficient ( h e , i / h e ).