Abstract
This study investigated the effect of adding two sister holes placed downstream the main hole on film cooling by employing large eddy simulation. Here, film-cooling flow fields from a triple-hole system inclined by 35° to a flat plate at blowing ratios of M = 0.5 and unity were simulated. Each sister hole supplies a cooling fluid at a flow rate that is a quarter of that for the main hole. The simulations were conducted using the Smagorinsky–Lilly model as the subgrid-scale model, and the results were compared with those for a single-hole system for the same amount of total cooling air and same cross-sectional area of the holes. Relative to the single-hole system, the spanwise-averaged film-cooling effectiveness in the triple-hole configuration at M = 1.0 increased by as much as 345%. The subsequent proper orthogonal decomposition analysis showed that the kinetic energy of a counter-rotating vortex pair in the triple-hole system dropped by 30–40% relative to that of the single-hole system. This indicates that the additional sister holes promoted the suppression of the mixing of the coolant jet with the mainstream flow, thus keeping the temperature of the latter low. Cross-sectional views of the root-mean-square temperature contours were also analyzed; with the results confirming that the effect of the sister holes on the jet trajectory greatly contributes in promoting film-cooling effectiveness as compared to the effect of the reduced mixing.
Highlights
The principle of idealized Brayton cycle states that gas turbine efficiency can be improved by increasing the inlet temperature of the turbine [1]
Considering the above, this paper aims to investigate the effect of a triple-hole system on film-cooling performance on a flat plate at blowing ratios of 0.5 and 1.0
The centerline effectiveness decreased as the main flowevaluated traveled on the the adiabatic film-cooling effectiveness in the single-hole system was downstream
Summary
The principle of idealized Brayton cycle states that gas turbine efficiency can be improved by increasing the inlet temperature of the turbine [1]. Various cooling methods can be employed, among which the film-cooling technique has been widely used. In this technique, the cooling air which is bled from the compressor is injected through holes on the turbine blade surface—this reduces the surface temperature and protects the surface from the main flow. Substantial investigations of the physics of film cooling in such a cylindrical hole system have revealed that a single cylindrical hole can be relatively vulnerable to the generation of the jet liftoff [2] and that a specific hole arrangement could produce film cooling that provides better thermal protection than single cylindrical holes do. Specific hole arrangements make the intended vortex interactions between film cooling jets to increase film-cooling effectiveness
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