Investigations on the aerothermal performance of the turbine blade winglet squealer tip within an uncertainty framework

Abstract

A improved efficient uncertainty quantification analysis framework is proposed by the combination of sparse Polynomial Chaos Expansion (PCE) and Universal Kriging (UK) metamodel to obtain the surrogate model. Meanwhile a challenging analytical test function and an engineering test are considered to investigate the response performance of UK-PCE method. The results show that the UK-PCE method reduces the computational cost by more than 70% in comparison to the typical PCE method. Then this method was applied to the uncertainty quantification of the effect of the Conventional Squealer Tip (CST) and Winglet Squealer Tip (WST) on the aerodynamic and heat transfer performance of GE-E3 rotor blade tip. Additionally, the Sobol Indice method is carried out as a global parameter sensitivity analysis to identify the key parameters for aerothermal performance of the CST and WST. Wherein, the inlet total pressure, inlet total temperature and inlet flow angle is considered as flow condition uncertainty parameters and tip clearance are considered as geometrical uncertainty parameters. The influence mechanisms of the uncertainty parameters on the aerothermal performance of the CST and WST are investigated by detailed flow and thermal field analysis. According to the results of the uncertainty quantification calculation, the mean values of leakage flow rate of both CST and WST have increased remarkably compared with the design values, and it is worth nothing that the increase of the mean value and the standard deviation of leakage flow rate of WST is much larger than that of CST. Therefore, in actual operation, the ability of WST to control the leakage flow rate will be much lower than expected. Further, the study of heat transfer performance uncertainty quantification shows that the mean value and standard deviation of the heat flux of WST are larger than that of CST, indicating that the use of winglet structure will instead make the heat transfer performance of the blade tip worse in actual operation. The result of sensitivity analysis reveals that the tip clearance is the parameter that contributes most to the uncertainty of the aerothermal performance of CST and WST, so the geometric accuracy of the tip clearance should be strictly ensured in the turbine blade assembly and marching process. What needs to be noted is that the influence of the inlet total temperature on the uncertainty of the heat transfer performance of the CST and WST is also not negligible, hence a satisfactory control system should be designed in the actual operation of gas turbine so the fluctuation of inlet total temperature can be attenuated rapidly.