Flow and heat transfer characteristics of double-wall cooling with multi-row short film cooling hole arrangements

The double-wall cooling systems with internal jet impingements and external film cooling are greatly applicable in modern turbine blades, providing enhanced cooling capabilities compared to the conventional passage cooling. This paper presents experimental and numerical results of flow and heat transfer characteristics of a double-wall cooling configuration, which has an inline short film cooling hole arrangement. A transient infrared thermography technique was used in this study, and managed to obtain the external-wall adiabatic film cooling effectiveness and heat transfer coefficients during a single transient test. A series of steady-state Reynolds Averaged Navier-Stokes (RANS) simulations adopting polyhedral meshes and the Shear-Stress Transport (SST) k−ω turbulence model were conducted to characterize internal heat transfer as well as overall cooling effectiveness. Of interest are the influences of blowing ratio on flow and heat transfer, the characteristics with the inline short film cooling hole arrangement, and the effects of wall thickness on film cooling effectiveness. On the basis of validations with experiments, the numerical computations revealed that the internal heat transfer dominants double-wall cooling performance with the inline short hole arrangement. Comparing to the staggered arrangement, the inline arrangement can achieve comparable cooling performance with a lower pressure loss for the coolant, which is due to the better complementarity between internal and external heat transfer, as well as a less deteriorated parameter of net heat flux reduction (NHFR) at the high blowing ratio. Moreover, the short hole effect in the double-wall cooling leads to the decreased adiabatic film cooling effectiveness on the external surface especially when the BR is higher than 0.3 and the L/Df is lower than 1.5, and this is caused by the in-hole anti-vortex interacting with the mainstream flow. Additionally, the correspondences between the flow structure and heat transfer characteristics in the double-wall cooling are described in this paper.