Film Cooling Effectiveness Measurements on Trailing Edge Cutback Surface and Lands Following Novel Cross Corrugated Slot Geometry

Abstract

The trailing edge of the high pressure turbine blade presents significant challenges to the turbine cooling engineer. A novel cooling design using cross corrugated slots for the trailing edge has been proposed. This geometry allows blade designers to finely tune pressure loss and consequently coolant flow through the slot, but potentially results in poor film cooling performance downstream of the slot exit, an effect that could be mitigated with exit shaping. The current study is focused on comparing film cooling effectiveness on the cutback surface and lands with a plain rectangular slot under the same conditions. A set of nine cross corrugated internal slot geometries has been investigated in a large scale model of the trailing edge pressure side ejection slot exit. Four geometries used a 90° included angle with variations to the channel alignment at slot exit. Four used a 120° included angle, with the same variations to the exit alignment. The final geometry used a 90° included angle with exit shaping. Pressure sensitive paint was used to measure adiabatic film cooling effectiveness at five blowing ratios ranging from 0.6 to 1.4 in increments of 0.2. High resolution 2D distributions of film cooling effectiveness both on the cutback surface and the top of the lands were recorded. It was found that unmodified cross corrugated slots do result in poor film effectiveness on the cutback surface compared to a plain rectangular slot. However, land cooling is slightly improved, and applying exit shaping to the cross corrugated slot results in effectiveness levels at the trailing edge on par with or even superior to the rectangular slot at blowing ratios of 0.8 or below. Therefore, in this respect, the novel cross corrugated slot design proposed is a viable candidate for blade design, provided exit shaping is used and low blowing ratios are expected.

High Resolution Experimental and Computational Methods for Modelling Multiple Row Effusion Cooling Performance

“…As noted by Wong et al [19], PtTFPP is a luminophore that responds when exposed to light of a certain wavelength. This response is quenched by the interaction with oxygen, and consequently, the intensity of the emitted light decreases as the partial pressure of oxygen in contact with the PSP increases.…”

“…This drops to around 1.4% for effectiveness values greater than 0.8. For further details on the uncertainty associated with this PSP experimental rig setup, please see Wong et al [19], where this is discussed in greater detail.…”

“…A brief overview of the pressure sensitive paint (PSP) measurement technique is provided here, but the reader is referred to Wong et al [19], Gurram et al [20] and Han and Rallabandi [21] for further details.…”

“…Intensity images of the experiments were captured using a 1928 × 1452 resolution, monochromatic CCD camera (Allied Vision Technologies Bigeye G-283B, supplied by Stemmer Imaging, Tongham, UK) with a 610 nm-long pass filter. The in-house MATLAB (version R2015b, MathWorks, Cambridge, UK) post-processing method developed by Wong et al [19] was utilised in calculating film effectiveness from the raw image data. It is noted that, following the perturbation method discussed by Moffat [22], the greatest uncertainty in film effectiveness values occur at lower effectiveness where for an effectiveness of around 0.14, the associated uncertainty is 3.1%.…”

High Resolution Experimental and Computational Methods for Modelling Multiple Row Effusion Cooling Performance

“…A brief overview of the PSP measurement technique is provided here, but the reader is referred to Wong et al (2016), Gurram et al (2016), and Han and Rallabandi (2010) for further details.…”