Numerical Analysis of Film Cooling Due to Simple/Compound Angle Hole Combination

Abstract

Film cooling technique is one of the gas turbine components saving from thermal failure. This article presents a numerical study of film cooling effectiveness due to two rows of simple and compound angle holes. The holes are inclined with 30° on a flat surface for all studied cases. Two orientation angles of the film cooling holes are applied (0° and 30°). Six cases are used to represent different configurations for the two rows. Three different values of velocity ratios (namely 0.5, 1.0 and 2.0) are represented during this study. The numerical model is validated through comparing the results of single row with simple holes with the available experimental works in the literature. As an interesting observation, it is found that the staggered arrangement provides better film cooling effectiveness than the in-line one for zero orientation angle configurations, while the in-line arrangement represents the highest effectiveness if all holes in the two rows have 30° orientation angle. The enhancement ratio of overall effectiveness corresponding to averaged film cooling has been calculated. The maximum enhancement ratio has been achieved with compound/compound in-line configuration with about 336.5% at velocity ratio equal 2. Using compound angle holes enhances the film cooling effectiveness with inline arrangement, while using it with staggered arrangement reduces the overall averaged film cooling effectiveness, especially at high velocity ratio. Keywords Film cooling • Gas turbine • Two rows • Compound angle • CFD List of Symbols D Film cooling hole diameter (m) VR Velocity ratio = U c /U m M Blowing ratio = (ρ c U c /ρ m U m ) ER Enhancement ratio MR Momentum ratio = (ρ c U c 2 /ρ m U m 2 ) DR Density ratio = ρ c /ρ m Re x Freestream Reynolds number = U m × x/ν m Re D Injectant Reynolds number = U c × D/ν c P Distance between two consecutive holes T aw Adiabatic wall temperature (K) T c Coolant air temperature (K) T f Local film temperature (K) T m Mainstream air temperature (K) Tu Turbulence intensity U c Coolant air velocity (m/s) U m Mainstream air velocity (m/s) x Distance from the upstream row centerline (m) ν Kinematic viscosity of the fluid (m 2 /s) Average film cooling effectiveness Overall film cooling effectiveness SSI

Effect of protrusion shape on film cooling performance for the cylindrical hole embedded in a contoured crater

“…The discrete hole with a cylindrical shape was suggested as the appropriate one and then commonly applied in practice due to its simplicity and lower manufacturing cost. The early studies [2][3][4][5] revealed that the blowing ratio significantly influences the cylindrical hole's cooling performance. They concluded that the effectiveness tends to increase with the increase of blowing ratio when the blowing ratio is lower than 0.5 but deteriorates sharply when the blowing ratio exceeds 0.5.…”

“…cooling effectiveness profile Fig.4Grid independence test for the cratered hole with arc protrusion at M=0 5. …”

Numerical study of film cooling effectiveness of a gas turbine blade under variable blowing ratio and turbulence intensity

“…Most research has been done by the RANS approach with the k –$$\varepsilon $$ turbulence method to simulate the film cooling of the typical blades 12 . The main parameters involved in the film cooling phenomena (blowing ratio, turbulence intensity, hole angle, hole geometry, in stagger and in‐line hole arrangement, hole to hole distance, coolant velocity, and temperature) are examined in various studies 13–25 …”

“…The results revealed that the film cooling efficiency was significantly enhanced by changing a single hole with a multi‐hole shape. Abdelmohimen et al 21 numerically investigated the effect of film cooling on a flat plate by applying two rows of simple and compound angle holes in stagger an in‐line arrangement. They found that applying compound angle holes with in‐line configuration increase the film cooling performance but applying it in staggered configuration at a high‐velocity ratio decrease the film cooling performance.…”

“…12 The main parameters involved in the film cooling phenomena (blowing ratio, turbulence intensity, hole angle, hole geometry, in stagger and in-line hole arrangement, hole to hole distance, coolant velocity, and temperature) are examined in various studies. [13][14][15][16][17][18][19][20][21][22][23][24][25] Leylek et al [13][14][15][16] performed their studies in film cooling physics in four-part complement papers. In Part I, Walters and Leylek 13 analyzed the flow structures discover in film cooling holes and the area of the jet's interaction in the cross-flow.…”