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research-article

Experimental Study of Periodic Free Stream Unsteadiness Effects on Discrete Hole Film Cooling in Two Geometries

[+] Author and Article Information
Daniel Borup

Dept. of Mechanical Engineering, Stanford University, Stanford, California 94305
borup@stanford.edu

Danyang Fan

Dept. of Mechanical Engineering, Stanford University, Stanford, California 94305
danfan17@stanford.edu

Dr. Christopher J. Elkins

Dept. of Mechanical Engineering, Stanford University, Stanford, California 94305
celkins@stanford.edu

Dr. John Eaton

Dept. of Mechanical Engineering, Stanford University, Stanford, California 94305
eatonj@stanford.edu

1Corresponding author.

ASME doi:10.1115/1.4041866 History: Received October 09, 2018; Revised October 22, 2018

Abstract

Accurate prediction of the heat transfer near film cooling holes is critical, and high-fidelity experimental data sets are needed for validation of new computational models. Relatively few studies have examined the effects of periodic main flow unsteadiness resulting from the interaction of turbine blades and vanes, with a particular lack of data for shaped hole configurations. Periodic unsteadiness was generated in the main flow over a laidback, fan-shaped cooling hole at a Strouhal number (St = fD/U) of 0.014 by an airfoil oscillating in pitch. Magnetic Resonance Imaging (MRI) was used to obtain full-field, phase-resolved velocity and scalar concentration data for a hole Reynolds number of 2900, channel Reynolds number of 25,000, and blowing ratio of unity. Both mean and phase-resolved data are compared to previous measurements with steady main flow. The periodic unsteadiness was characterized by alternating periods of slow main flow, which allowed coolant to penetrate into the freestream along the centerplane, and fast, hole-impinging main flow, which deflected coolant towards the laidback wall and caused coolant ejection away from the centerplane. Mean adiabatic surface effectiveness was reduced up to 23% inside the hole, while mean laterally-averaged effectiveness outside the hole fell 28- 36% over the entire measurement domain. A brief comparison to a round jet with and without unsteadiness is included; for the round jet, no disturbance was observed inside the hole, and some fluctuations directed coolant towards the wall, which increased mean film cooling effectiveness.

Copyright (c) 2018 by ASME
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