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Research Papers

Computational Fluid Dynamics Evaluations of Film Cooling Flow Scaling Between Engine and Experimental Conditions

[+] Author and Article Information
James L. Rutledge

Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH 45433
e-mail: james.rutledge@us.af.mil

Marc D. Polanka

Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH 45433

Nathan J. Greiner

Air Force Research Laboratory,
Wright-Patterson Air Force Base, OH 45433

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 3, 2016; final manuscript received August 17, 2016; published online September 27, 2016. Editor: Kenneth Hall.This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Turbomach 139(2), 021004 (Sep 27, 2016) (7 pages) Paper No: TURBO-16-1186; doi: 10.1115/1.4034557 History: Received August 03, 2016; Revised August 17, 2016

The hostile turbine environment requires testing film cooling designs in wind tunnels that allow for appropriate instrumentation and optical access, but at temperatures much lower than in the hot section of an engine. Low-temperature experimental techniques may involve methods to elevate the coolant to freestream density ratio to match or approximately match engine conditions. These methods include the use of CO2 or cold air for the coolant while room temperature air is used for the freestream. However, the density is not the only fluid property to differ between typical wind tunnel experiments so uncertainty remains regarding which of these methods best provide scaled film cooling performance. Furthermore, matching of both the freestream and coolant Reynolds numbers is generally impossible when either mass flux ratio or momentum flux ratio is matched. A computational simulation of a film cooled leading edge geometry at high-temperature engine conditions was conducted to establish a baseline condition to be matched at simulated low-temperature experimental conditions with a 10× scale model. Matching was performed with three common coolants used in low-temperature film cooling experiments—room temperature air, CO2, and cold air. Results indicate that matched momentum flux ratio is the most appropriate for approximating adiabatic effectiveness for the case of room temperature air coolant, but matching the density ratio through either CO2 or cold coolant also has utility. Cold air was particularly beneficial, surpassing the ability of CO2 to match adiabatic effectiveness at the engine condition, even when CO2 perfectly matches the density ratio.

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Figures

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Fig. 1

Coordinate system and hole geometry

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Fig. 2

Computational domain

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Fig. 3

Surface mesh near coolant hole

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Fig. 4

Fluid region mesh on constant x–z plane bisecting intersection of the coolant hole with the leading edge

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Fig. 5

M = 1.0 adiabatic effectiveness, η, with unit density ratio air coolant (arrows indicate direction of coolant and freestream)

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Fig. 6

Experimental validation of spanwise-averaged adiabatic effectiveness

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Fig. 7

M = 1.0 adiabatic effectiveness, η, at engine conditions, DR = 2

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Fig. 8

Adiabatic effectiveness at x/d = 3 for engine-scale conditions and experimental conditions with various coolant flow rate parameters matched for room temperature air and cold air coolants

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Fig. 9

Spanwise-averaged adiabatic effectiveness for engine-scale conditions and experimental conditions with various coolant flow rate parameters matched for room temperature air and cold air coolants

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Fig. 10

Adiabatic effectiveness at x/d = 3 for engine-scale conditions and experimental conditions with various coolant flow rate parameters matched for CO2 and cold air coolants

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Fig. 11

Adiabatic effectiveness at x/d = 3 for engine-scale conditions (with DR = 1.5) and experimental conditions with various coolant flow rate parameters matched for CO2 and cold air coolants (note change in scale)

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Fig. 12

Adiabatic effectiveness at x/d = 3 for engine-scale conditions (with DR = 1.5) and experimental conditions with cold air coolant, CO2 coolant, and a fictitious gas that provides matching of all property ratios

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Fig. 13

Normalized density as a function of nondimensional temperature or species concentration

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