2D and 3D thermoelastic phenomena in double wall transpiration cooling systems for gas turbine blades and hypersonic flight

Multiscale analysis of thermomechanical stresses in double wall transpiration cooling systems for gas turbine blades

“…All the above indicate that several effects need to be considered when minimising stresses through changing geometry for combined T-CF loading. Most of the effects however arise in the general case of flat walls with free ends where non-zero wall rotations can occur [34], which is not the case in a turbine blade [34].…”

“…We now analyse a particular 3D case of more relevance to the turbine blade of Fig 3, which consists of cylindrical double walls [34] with sufficient length and constant external radius of curvature, 𝑅. By updating the kinematic equations (Eqs (1a-b)) to account for the Poisson's ratio, 𝜈, effect and by postulating zero total bending curvatures, the theoretical 2D solution (Eqs (1)) for flat walls, based on classical beam theory, can be extended into an approximate 3D solution for cylindrical walls, based on flat plate theory; the solution is provided in Appendix D [34]. The solution is exact for flat systems (and cylindrical systems of 𝑅/𝑡 → ∞) and remains an accurate approximation for cylindrical systems of low curvature, i.e.…”

“…In contrast to the aerothermal aspects of DWTC, systematic studies of the mechanical performance is limited to a few recent studies [12,[32][33][34], mainly conducted by the authors. These studies indicate that DWTC systems can experience severe thermal stresses [34] as significant stress concentration factors (SCF) occur at holes and pedestals [12]. Values of SCF ≈ 4 at the acute wedge (Fig 1b) of inclined film holes have been shown to cause severe local cyclic plasticity and low cycle fatigue failure (LCF) [13].…”

“…-In [34] it was assumed that a thermal gradient develops only across the outer hot wall. The thermal gradient which in practise occurs across the pedestal [7], will enhance the wall temperature mismatch, increasing the thermal stresses in both walls.…”

“…-Centrifugal (CF) loading has been ignored so far [12,[32][33][34], despite its significance in turbine blades [36]. Since CF loading is generally tensile, the thermally (T) induced compressive film hole stresses can eventually reduce and the tensile stresses at internal features may increase.…”