Unsteady adiabatic film cooling effectiveness behind shaped holes

Abstract

Gas turbine as a vital component requires higher inlet temperature to improve its thermal efficiency, and thus a thin coolant film spreads over the blade surface to isolate it from hot gases. However, such coolant intensively interacts with the mainstream, leading to highly unsteady coolant coverage, which damages structural integrity, challenging its reliable and sustainable operations. Consequently, fast-response pressure-sensitive paint technique (fast-PSP) was used to measure the coolant unsteadiness behind the shaped holes, considering plenum and crossflow feeds. A steady-RANS simulation was performed to predict the large-scale flow structures and explain the mean results. The measured standard deviation (SD) and fluctuating components were used to uncover the spatial-temporal features associated with the predicted vortical structures. The mean effectiveness was dramatically influenced by the blowing ratios (M), showing attached flow at a low M and lift-off at a high M. The internal crossflow showed asymmetric spreading, resulting in deteriorated performance behind the holes. The unsteadiness was highly influenced by the energetic vortical structures, which originated from the hole entrance, forming in-hole counter-rotating vortex pair (CRVP) and vortex-tube structures. Meanwhile, the vortex-tube formed a swirl-vortex signature downstream of the hole-trailing-edge, leading to asymmetric CRVP. The swirl-vortex interacted with the CRVP windward-leg and reduced the spreading behind the holes, leading to mainstream ingestions. The combined results suggested considering the internal flow effects, which could help the designers understand the characteristics of unsteady effectiveness; promoting advanced cooling strategies for enhanced protection of future gas turbines.

Keywords

• Film cooling
• Unsteady flow structure
• Fast-PSP
• Internal crossflow
• Shaped holes