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Measurements in discrete hole film cooling behavior with periodic freestream unsteadiness

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Abstract

Magnetic resonance imaging (MRI) techniques were used to investigate a discrete, \(30^{\circ }\)-inclined round jet in crossflow subjected to periodic freestream unsteadiness. The freestream perturbations were generated by an oscillating airfoil upstream of the jet. The experiment operated at a Strouhal number of 0.014, channel Reynolds number of 25,000, hole Reynolds number of 2900, and jet blowing ratio of unity. 3D phase locked velocity measurements were obtained over the entire channel using magnetic resonance velocimetry (MRV). 3D time-averaged temperature measurements were acquired using magnetic resonance thermometry (MRT), along with phase-locked temperature measurements in the 2D centerplane of the channel and jet. The freestream flow just upstream of the jet was characterized by streamwise velocities ranging from \(0.88 U_\text {bulk}\) to \(1.23 U_\text {bulk}\) and wall-normal velocities from \(-0.11 U_\text {bulk}\) to \(0.02 U_\text {bulk}\). Flow inside the hole was observed to be insensitive to the freestream fluctuations, as velocities and temperatures in the hole remained largely unchanged throughout the cycle. Outside the hole, changes to the streamwise velocity produced an oscillating jet blowing ratio that led to the lengthening and shortening of the counter-rotating vortex pair (CVP) as well as a varying degree of coolant separation from the film cooled wall. During one portion of the cycle, downwashing freestream flow (i.e., flow with negative wall-normal velocities) promoted strong re-attachment and lateral spreading of the jet. Mean, spanwise-averaged film cooling effectiveness values were compared to those of an earlier experiment with a steady freestream and identical geometry, Reynolds number, and blowing ratio. Film cooling performance in the near-hole region was higher with steady freestream flow. However, at downstream locations, the downward transport of coolant by the periodic downwashing flow led to a higher mean surface effectiveness than in the steady case.

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Acknowledgements

Research funding was provided by Honeywell International Inc. Daniel Borup is supported by an Office of Technology Licensing Stanford Graduate Fellowship and a National Science Foundation Graduate Research Fellowship (Grant No. DGE-114747). The authors are grateful for the use of MRI facilities at the Richard M. Lucas Center for Imaging at Stanford University.

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  1. Flow Physics and Computational Engineering Group, 488 Escondido Mall, Bldg. 500, Stanford, CA, 94305, USA

    Danyang Fan, Daniel D. Borup, Christopher J. Elkins & John K. Eaton

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  1. Danyang Fan
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  2. Daniel D. Borup
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  3. Christopher J. Elkins
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  4. John K. Eaton
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Correspondence to Daniel D. Borup.

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Fan, D., Borup, D.D., Elkins, C.J. et al. Measurements in discrete hole film cooling behavior with periodic freestream unsteadiness. Exp Fluids 59, 37 (2018). https://doi.org/10.1007/s00348-018-2493-4

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  • DOI: https://doi.org/10.1007/s00348-018-2493-4

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