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Experiments in Fluids

, 56:211 | Cite as

Focusing-schlieren visualization in a dual-mode scramjet

  • Toshinori KouchiEmail author
  • Christopher P. Goyne
  • Robert D. Rockwell
  • James C. McDaniel
Research Article

Abstract

Schlieren imaging is particularly suited to measuring density gradients in compressible flowfields and can be used to capture shock waves and expansion fans, as well as the turbulent structures of mixing and wake flows. Conventional schlieren imaging, however, has difficulty clearly capturing such structures in long-duration supersonic combustion test facilities. This is because the severe flow temperatures locally change the refractive index of the window glass that is being used to provide optical access. On the other hand, focusing-schlieren imaging presents the potential of reduced sensitivity to thermal distortion of the windows and to clearly capture the flow structures even during a combustion test. This reduced sensitivity is due the technique’s ability to achieve a narrow depth of focus. As part of this study, a focusing-schlieren system was developed with a depth of focus near ±5 mm and was applied to a direct-connect, continuous-flow type, supersonic combustion test facility with a stagnation temperature near 1200 K. The present system was used to successfully visualize the flowfield inside a dual-mode scramjet. The imaging system captured combustion-induced volumetric expansion of the fuel jet and an anchored bifurcated shock wave at the trailing edge of the ramp fuel injector. This is the first time successful focusing-schlieren measurements have been reported for a dual-mode scramjet.

Keywords

Shock Wave Turbulent Structure Stagnation Temperature Fresnel Lens Shock Cell 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

a

Unobstructed source image height

C

Contrast of image

f#

f-Number of lens

F

Focal length of the schlieren lens

H

Ramp injector-surface-normal height

Iij

Local image intensity

\(\hat{I}\)

Spatial-average intensity in an interrogation area of a schlieren image

l

Distance from schlieren lens to object

l

Distance from schlieren lens to imaging plane

L

Distance from schlieren lens to source grid

L

Distance from schlieren lens to cutoff grid

pk

Kernel size for Gaussian filter

P0

Stagnation pressure

PW

Static wall pressure

T0

Stagnation temperature

x, y, z

Streamwise, heightwise, and spanwise directions

α

Filter control parameter

ε

Refraction angle due to density gradient

Φ

Fuel equivalence ratio

σg

Standard deviation for Gaussian filter

\(\hat{\sigma }\)

Standard deviation of image intensity in an interrogation area of a schlieren image

Notes

Acknowledgments

The authors appreciate the assistant of Dr. Roland Krauss and Mr. Roger Reynolds in operating the supersonic combustion facility. This work was supported by Young Researcher Oversea Study Program of the Japan Society for the Promotion of Science. This research was also supported by the National Center for Hypersonic Combined Cycle Propulsion Grant FA 9550-09-1-0611. The technical monitors on the Grant were Chiping Li (AFOSR), and Aaron Auslender and Rick Gaffney (NASA).

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Toshinori Kouchi
    • 1
    Email author
  • Christopher P. Goyne
    • 2
  • Robert D. Rockwell
    • 2
  • James C. McDaniel
    • 2
  1. 1.Department of Mechanical and System EngineeringOkayama UniversityOkayamaJapan
  2. 2.Department of Mechanical and Aerospace EngineeringUniversity of VirginiaCharlottesvilleUSA

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