Highly Turbulent Mainstream Effects on Film Cooling of a Simulated Airfoil Leading Edge

Abstract

The influence of a high mainstream turbulence was examined in an experimental study of film cooling on a simulated turbine blade leading edge. Detailed heat transfer coefficient and adiabatic effectiveness values were measured under conditions representative of actual environments in a gas turbine engine. The two parameters were also combined for a net heat flux reduction analysis. Turbulence levels of Tu = 17% were achieved by modifying a cross-jets turbulence generator with a large cylinder element. A quarter cylinder geometry was used to simulate the turbine blade leading edge. Two staggered rows of nine holes each were incorporated with a geometry consistent with current industry design practices. One row was positioned nominally on the stagnation line, x/d = 0, while the other was located 25° from the stagnation line. The holes were spaced at S/d = 7.64 with a shallow injection angle of 20° and oriented at 90° to the streamwise direction. Comparisons were made to previous studies of heat transfer rates and adiabatic effectiveness values under low turbulence (Tu < 0.5%) conditions. Adiabatic effectiveness was generally decreased by about 20% due to the high mainstream turbulence, although a much greater decrease occurred at the stagnation line at lower blowing rates. The relative increase in heat transfer coefficient due the coolant injection was found to be significantly smaller for the high mainstream turbulence case compared to the low mainstream turbulence case. This was particularly important when evaluating the overall performance of this film cooling hole configuration, since the much smaller relative increase in heat transfer coefficient resulted in good performance in terms of net heat flux reduction.

CFD Predictions of Heat Transfer Coefficient Augmentation on a Simulated Film Cooled Turbine Blade Leading Edge

“…Since one of the purposes of the present study was to compare the computational prediction of heat transfer coefficients with experimental data, the geometry of the leading edge used in these simulations was identical to the computational study carried out by Dobrowolski et al (2009) and as close as possible to the physical model employed by Yuki et al (1998) and Johnston et al (1999). However it should be pointed out that these studies had a quarter circle model with a suction slot on the bottom whereas the present study used a half cylinder model.…”

“…In this section, computational predictions of the heat transfer coefficient augmentation were compared with experimental data from Yuki et al (1998) and Johnston et al (1999) because these studies are the only experimental data that had the same commonly used round hole configuration. However it should be acknowledged that their model was not a full leading edge thus this was not a perfect comparison.…”

“…York and Leylek (2002) conducted realizable k-ε heat transfer coefficient simulations on a leading edge model identical to the one used by Yuki et al (1998) and Johnston et al (1999), i.e. a quartercylinder with a flat afterbody.…”

Effects of High Intensity, Large-Scale Freestream Combustor Turbulence on Heat Transfer in Transonic Turbine Blades

“…Factors such as the film cooling blowing rate, freestream turbulence level and curvature will have a large effect on the results. This is evidenced by the ratios of film DATA ANALYSIS AND RESULTS cooled heat transfer coefficient and baseline heat transfer coefficient (h o,c /h o ), which in the work of Johnston, et al (1999) are between 1.3 and 1.5 in areas of curvature, where in Smith, et al (2000) this ratio is between 1.06 and 1.26. …”

“…As a comparison with this data, if the low, turbulence no film-cooling data on the suction surface (Table 3.1 and Smith, et al, 2000) is compared to the high turbulence, suction surface film cooling data in Table 3.10, the result would be a ratio (h t,c /h o ) of approximately 1.16-1.34. Johnston, et al (1999) reported data of this type for heat transfer data with film cooling and high freestream turbulence on a quarter cylinder model. They reported ratios as high as 1.6 on areas with curvature, which is significantly higher than the predicted data in the current work.…”