Abstract
The objective of this study is to investigate the effects of oscillations in the main flow and the coolant jets on film cooling at various frequencies (0 to 2144 Hz) at low and high average blowing ratios. Numerical simulations are performed using LES Smagorinsky–Lilly turbulence model for calculation of the adiabatic film cooling effectiveness and using the DES Realizable k-epsilon turbulence model for obtaining the Stanton number ratios (St/Sto). Additionally, multi-frequency inlet velocities are applied to the main and coolant flows to explore the effects of multi-frequency unsteady flows and the results are compared to those at single frequencies. The results show that at a low average blowing ratio (M = 0.5) if the oscillation frequency is increased from 0 to 180 Hz, the effectiveness decreases and the Stanton number ratio increases. However, when the frequency goes from 180 to 268 Hz, the effectiveness sharply increases and the Stanton number ratio increases slightly. If the frequency changes from 268 to 1072 Hz, the film cooling effectiveness decreases and the Stanton number ratio increases slightly. If the frequency goes from 1072 to 2144 Hz, the film cooling effectiveness climbs up and the Stanton number ratio decreases. The results show that at high average blowing ratio (M = 1.0) the trends of the film cooling effectiveness are similar to those at low blowing ratio (M = 0.5) except from 0 to 90 Hz. If the frequency goes from 0 to 90 Hz at M = 1.0, the film cooling effectiveness increases and the Stanton number ratio decreases. It can be said that it is important to include the effects of oscillating flows when designing film cooling systems for a gas turbine.
Highlights
The gas turbine industry made an effort to increase the turbine inlet temperature and modern advanced gas turbines have a turbine inlet temperature near 1600 ◦ C [1], which is about 200 degrees hotter than the melting point of nickel-iron alloys which are frequently used as the material of gas turbines [2]
The current study investigates the effects of oscillations in the main flow and coolant jet on film cooling on a flat plate geometry with an inline cylindrical hole with a 35◦ inclined injection angle for average blowing ratios of M = 0.5 and 1.0 using numerical simulations
Cooling effectiveness the investigated andcells the descriptions thesame grids usedfor arethe shown in Table
Summary
The gas turbine industry made an effort to increase the turbine inlet temperature and modern advanced gas turbines have a turbine inlet temperature near 1600 ◦ C [1], which is about 200 degrees hotter than the melting point of nickel-iron alloys which are frequently used as the material of gas turbines [2]. The coolant is injected through holes on the turbine blade surface or the inner surface of the combustion chamber as shown in Figures 1 and 2. The injected coolant is bent by the main flow momentum and forms a thin coolant film on the surface resulting in the protection of the surface from the hot main flow. The film cooling reduces the adiabatic wall temperature, the temperature of the Inventions 2018, 3, 73; doi:10.3390/inventions3040073 www.mdpi.com/journal/inventions
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