Theoretical analysis method of fluid-thermal-structural coupling and its influence mechanism analysis for double wall turbine blade

Double wall cooling is regarded as one of the most promising technologies to raise turbine inlet temperature required by the next-generation aeroengines. However, intense fluid-thermal-structural coupling induced by numerous dense micro cooling features severely hinders its practical application. In this study, a basic theoretical analysis model is established to clarify the coupling mechanism, verified and discussed in detail with engineering practice. Numerical simulation is then performed on typical turbine blades with single and double wall structures, and the coupling characteristics of flow, heat transfer, and strength are analyzed and discussed. Theoretical analysis indicates that the double wall structure achieves high cooling effectiveness but generates large temperature difference between the inner and outer walls, mainly ranging from 100 K to 300 K. Under large temperature difference, incompatible thermal expansion of inner and outer walls causes mutual constraint and produces high thermal stress, with outer wall undergoing compressive stress while inner wall undergoes tensile stress. Numerical results confirm these characteristics that there is an average temperature difference of 159 K between inner and outer wall, increasing their thermal stress by 86% and 21% respectively compared with single wall blade. Combined with the tensile centrifugal stress, the mechanism of double wall structure, caused by the fluid-thermal-structural coupling, can be summarized: the outer wall mainly bears high temperature while the inner wall mainly bears mechanical load. This study provides a better understanding of the rationale of double wall structure to improve the design and optimization of double wall turbine blade.