The Effect of Meter-Diffuser Offset on Shaped Film Cooling Hole Adiabatic Effectiveness

[+] Author and Article Information
Shane E. Haydt

Mechanical and Nuclear Engineering Department The Pennsylvania State University University Park, PA 16802, USA

Stephen Lynch

Mechanical and Nuclear Engineering Department The Pennsylvania State University University Park, PA 16802, USA

Scott D. Lewis

Turbine Durability United Technologies-Pratt & Whitney 400 Main Street East Hartford, CT 06108, USA

1Corresponding author.

ASME doi:10.1115/1.4036199 History: Received November 18, 2016; Revised February 28, 2017


Shaped film cooling holes are used extensively in gas turbines to reduce component temperatures. These holes generally consist of a metering section through the material and a diffuser to spread coolant over the surface. These two hole features are created separately using electrical discharge machining, and occasionally an offset can occur between the meter and diffuser due to misalignment. The current study examines the potential impact of this manufacturing defect to the film cooling effectiveness for a well-characterized shaped hole known as the 7-7-7 hole. Five meter-diffuser offset directions and two offset sizes were examined, both computationally and experimentally. Adiabatic effectiveness measurements were obtained at a density ratio of 1.2 and blowing ratios ranging from 0.5 to 3. The detriment in cooling relative to the baseline 7-7-7 hole was worst when the diffuser was shifted upstream (aft meter-diffuser offset), and least when the diffuser was shifted downstream (fore meter-diffuser offset). At some blowing ratios and offset sizes, the fore meter-diffuser offset resulted in slightly higher adiabatic effectiveness than the baseline hole, due to a reduction in the high-momentum region of the coolant jet caused by a separation region created inside the hole by the fore meter-diffuser offset. Steady RANS predictions did not accurately capture the levels of adiabatic effectiveness or the trend in the offsets, but it did predict the fore offset's improved performance.

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