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Effect of surface cooling on second-mode dominated hypersonic boundary layer transition

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Abstract

Experiments were performed in the low-enthalpy AFRL Mach 6 Ludwieg Tube to investigate the effects of surface temperature on hypersonic boundary layer transition. The test article for all experiments was a 7-degree half-angle cone with a sharp nose tip. The model was designed with a large internal cavity, capable of containing pressurized cryogenic fluids. A cooling system utilizing liquid nitrogen was designed and integrated with the test section of the Ludwieg Tube, allowing for significant surface cooling of the test article while maintaining all other conditions, such as tunnel noise spectra. The reduction of the surface temperature to values below 110 K led to a wall-to-boundary layer edge temperature ratio of 1.4, while this ratio was 4.3 for the uncooled case. Boundary layer transition behavior was observed between freestream unit Reynolds numbers ranging from 2.2 million per meter to 25.9 million per meter. Instability waves within the boundary layer were captured via time-resolved Schlieren visualization using a continuous light source. The images confirmed Mack's second mode was present for both uncooled and cooled model experiments. Turbulence intermittency statistics and frequency content of the instabilities were computed via several image processing techniques. Reducing the surface temperature of the test article decreased the boundary layer thickness and subsequently increased the frequency of the most unstable waves. Overall, the cooling delayed the boundary layer transition to turbulence for all cases observed.

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adapted from Hill (2020)

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Abbreviations

\(M_{\infty }\) :

Freestream Mach number

\(P_{{DT}}\) :

Initial driver tube pressure

\(P_{0}\) :

Freestream stagnation pressure

QS:

First quasi-steady period of flow

QS2:

Second quasi-steady period of flow

\(\text{Re} _{\infty }\) :

Freestream unit Reynolds number

\(\text{Re} _{{x\_e,Tr}}\) :

Reynolds number at onset of transition, based on boundary layer edge conditions

\(T_{{DT}}\) :

Initial driver tube temperature

\(T_{0}\) :

Freestream stagnation temperature

\(T_{w} /T_{e}\) :

Wall-to-boundary layer edge temperature ratio

\(U_{\infty }\) :

Freestream velocity, m/s

x:

Axial distance along the centerline

\(\mu _{\infty } {\text{~}}\) :

Freestream dynamic viscosity, kg/(m·s)

\(\rho _{\infty }\) :

Freestream density, kg/m3

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Acknowledgements

The authors would like to thank Dr. Roger Kimmel of AFRL/RQHF for sponsoring this research and Lieutenant Braeden Sheets for operating the Ludwieg Tube. We also thank Dr. Ross Wagnild of Sandia Laboratories for insightful discussions. Additionally, the authors would like to thank Brian Crabtree and Chris Harkless of the AFIT Model Shop for their outstanding work in fabricating the test article, as well as Michael Ranft of AFIT for providing valuable guidance regarding working with cryogenics. The first six authors would like to acknowledge the support of the Hypersonic Vehicle Simulation Institute and the oversight of Dr. Russ Cummings.

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Authors and Affiliations

  1. Air Force Institute of Technology, WPAFB, Dayton, OH, USA

    Ryan Oddo, Jonathan L. Hill, Mark F. Reeder, Daniel Chin, Joshua Embrador & Jeffrey Komives

  2. Air Force Research Laboratory, WPAFB, Dayton, OH, USA

    Matthew Tufts & Matthew Borg

  3. Purdue University, West Lafayette, IN, USA

    Joseph S. Jewell

Authors
  1. Ryan Oddo
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  2. Jonathan L. Hill
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  3. Mark F. Reeder
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  4. Daniel Chin
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  5. Joshua Embrador
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  6. Jeffrey Komives
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  7. Matthew Tufts
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  8. Matthew Borg
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  9. Joseph S. Jewell
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Correspondence to Mark F. Reeder.

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Oddo, R., Hill, J.L., Reeder, M.F. et al. Effect of surface cooling on second-mode dominated hypersonic boundary layer transition. Exp Fluids 62, 144 (2021). https://doi.org/10.1007/s00348-021-03237-0

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  • DOI: https://doi.org/10.1007/s00348-021-03237-0

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