Designing against severe stresses at compound cooling holes of double wall transpiration cooled engine components

Abstract

Advanced thermal protection technology is key for allowing hotter gas turbine cycle temperatures towards minimising fuel consumption and emissions. While effusion holes are essential for reducing heat flux into the structure through the formation of an air cool layer between the hot gas flow and the solid, they can shorten component life due to local stress raising effects. Through Finite Element (FE) analysis, we evaluate the severity of these effects in double wall transpiration cooling (DWTC) systems under thermal loading and identify how mechanical performance can be improved by modifying global and local geometric features. Increasing effusion hole inclination to 60∘ to the surface normal leads to extreme stress concentration factors (SCFs), which can exceed 5. Eliminating ellipticity in the effusion hole surface is shown to offer enormous performance benefits, by decreasing the SCF by 50%. A narrow spacing between the wall-connecting pedestals implies shorter hole-hole and hole-pedestal distances, which also leads to a reduction of SCFs. Our elastic solutions can be readily used in fatigue life calculations based on Neuber type local strain approaches. They also establish the basis for understanding the response of the new systems under combined thermal-mechanical loading.