Influence of Coolant Density on Turbine Blade Film-Cooling With Compound-Angle Shaped Holes

Abstract

Adiabatic film-cooling effectiveness is examined systematically on a typical high pressure turbine blade by varying three critical flow parameters: coolant blowing ratio, coolant-to-mainstream density ratio, and freestream turbulence intensity. Three average coolant blowing ratios 1.0, 1.5, and 2.0; three coolant density ratios 1.0, 1.5, and 2.0; two turbulence intensities 4.2% and 10.5%, are chosen for this study. Conduction-free pressure sensitive paint (PSP) technique is used to measure film-cooling effectiveness. Three foreign gases — N2 for low density, CO2 for medium density, and a mixture of SF6 and Argon for high density are selected to study the effect of coolant density. The test blade features 45° compound-angle shaped holes on the suction side and pressure side, and 3 rows of 30° radial-angle cylindrical holes around the leading edge region. The inlet and the exit Mach number are 0.27 and 0.44, respectively. Reynolds number based on the exit velocity and blade axial chord length is 750,000. Results reveal that the PSP is a powerful technique capable of producing clear and detailed film effectiveness contours with diverse foreign gases. As blowing ratio exceeds the optimum value, it induces more mixing of coolant and mainstream. Thus film-cooling effectiveness reduces. Greater coolant-to-mainstream density ratio results in lower coolant-to-mainstream momentum and prevents coolant to lift-off; as a result, film-cooling increases. Higher freestream turbulence causes effectiveness to drop everywhere except in the region downstream of suction side. Results are also correlated with momentum flux ratio and compared with previous studies. It shows that compound shaped hole has the greatest optimum momentum flux ratio, and then followed by axial shaped hole, compound cylindrical hole, and axial cylindrical hole.

A Review of Hole Geometry and Coolant Density Effect on Film Cooling

“…22). However, Liu et al (2012) reported that the density ratio effect on turbine blade film cooling with compound angled shaped-hole (see Fig. 21) is not as significant as that with compound angled cylindrical hole reported by Narzary et al (2012).…”

“…Blades with leading-edge film-cooling array and suction-side film cooling were Fig. 21 Details of the test film-cooled blade with shaped cooling holes on the pressure and suction surfaces studied by studied by Liu et al (2012).…”

“…Dittmar et al (2002) studied different film cooling hole configurations on the suction (convex) surface and concluded that shaped holes provide better coverage at higher blowing ratios by resisting jet penetration into the mainstream. The effect of coolant to mainstream density ratio and an unsteady wake was studied by Rallabandi et al (2012) and Narzary et al (2012) or Liu et al (2012) using the pressure sensitive paint measurement method. Foreign gases with variable density (Nitrogen for DR = 1.0, CO2 for DR = 1.5 and a mixture of Ar + SF6 for DR = 2.5) were used to simulate realistic engine density ratios.…”