Abstract

An application of speckle photography techniques to unsteady gas flow measurements is presented. The instrumentation developed for the analysis of double-exposure photographs by digital signal processing is described. It is shown that 2-D velocity fields can be measured even when the flow is not perfectly 2-D. Accuracy and limitations of these techniques are discussed.

© 1983 Optical Society of America

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References

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  1. P. E. Dimotakis, F. D. Debussy, M. M. Koochesfahani, Phys. Fluids 24, 995 (1981).
    [CrossRef]
  2. R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).
  3. P. G. Simpkins, T. Dudderar, J. Fluid Mech. 89, 665 (1978).
    [CrossRef]
  4. R. Meynart, Appl. Opt. 19, 1385 (1980) and references contained therein.
    [CrossRef] [PubMed]
  5. R. Meynart, Rev. Phys. Appl. 17, 301 (1982).
    [CrossRef]
  6. D. E. Fitzjarrald, J. Phys. E 15, 911 (1982).
    [CrossRef]
  7. R. Meynart, Rev. Sci. Instrum. 53, 110 (1982).
    [CrossRef]
  8. G. E. Maddux, S. L. Moorman, R. R. Corwin, Air Force Flight Dynamics Laboratory report AFFDL-TM-78-109-FBE (1978).
  9. H. Kreitlow, T. Kreis, Proc. Soc. Photo-Opt. Instrum. Eng. 210, 18 (1980).
  10. B. Ineichen, P. Eglin, R. Dandliker, Appl. Opt. 19, 2191 (1980).
    [CrossRef] [PubMed]
  11. G. H. Kaufmann, A. E. Ennos, B. Gale, D. J. Pugh, J. Phys. E 13, 579 (1980).
    [CrossRef]
  12. A. Oppenheim, R. Schafer, Digital Signal Processing (Prentice-Hall, Englewood Cliffs, N.J., 1975).

1982 (3)

R. Meynart, Rev. Phys. Appl. 17, 301 (1982).
[CrossRef]

D. E. Fitzjarrald, J. Phys. E 15, 911 (1982).
[CrossRef]

R. Meynart, Rev. Sci. Instrum. 53, 110 (1982).
[CrossRef]

1981 (1)

P. E. Dimotakis, F. D. Debussy, M. M. Koochesfahani, Phys. Fluids 24, 995 (1981).
[CrossRef]

1980 (4)

H. Kreitlow, T. Kreis, Proc. Soc. Photo-Opt. Instrum. Eng. 210, 18 (1980).

G. H. Kaufmann, A. E. Ennos, B. Gale, D. J. Pugh, J. Phys. E 13, 579 (1980).
[CrossRef]

R. Meynart, Appl. Opt. 19, 1385 (1980) and references contained therein.
[CrossRef] [PubMed]

B. Ineichen, P. Eglin, R. Dandliker, Appl. Opt. 19, 2191 (1980).
[CrossRef] [PubMed]

1978 (1)

P. G. Simpkins, T. Dudderar, J. Fluid Mech. 89, 665 (1978).
[CrossRef]

1977 (1)

R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).

Corwin, R. R.

G. E. Maddux, S. L. Moorman, R. R. Corwin, Air Force Flight Dynamics Laboratory report AFFDL-TM-78-109-FBE (1978).

Dandliker, R.

Debussy, F. D.

P. E. Dimotakis, F. D. Debussy, M. M. Koochesfahani, Phys. Fluids 24, 995 (1981).
[CrossRef]

Dimotakis, P. E.

P. E. Dimotakis, F. D. Debussy, M. M. Koochesfahani, Phys. Fluids 24, 995 (1981).
[CrossRef]

Dudderar, T.

P. G. Simpkins, T. Dudderar, J. Fluid Mech. 89, 665 (1978).
[CrossRef]

Eglin, P.

Elkins, R. E.

R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).

Ennos, A. E.

G. H. Kaufmann, A. E. Ennos, B. Gale, D. J. Pugh, J. Phys. E 13, 579 (1980).
[CrossRef]

Fitzjarrald, D. E.

D. E. Fitzjarrald, J. Phys. E 15, 911 (1982).
[CrossRef]

Gale, B.

G. H. Kaufmann, A. E. Ennos, B. Gale, D. J. Pugh, J. Phys. E 13, 579 (1980).
[CrossRef]

Ineichen, B.

Jackman, G. R.

R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).

Johnson, R. R.

R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).

Kaufmann, G. H.

G. H. Kaufmann, A. E. Ennos, B. Gale, D. J. Pugh, J. Phys. E 13, 579 (1980).
[CrossRef]

Koochesfahani, M. M.

P. E. Dimotakis, F. D. Debussy, M. M. Koochesfahani, Phys. Fluids 24, 995 (1981).
[CrossRef]

Kreis, T.

H. Kreitlow, T. Kreis, Proc. Soc. Photo-Opt. Instrum. Eng. 210, 18 (1980).

Kreitlow, H.

H. Kreitlow, T. Kreis, Proc. Soc. Photo-Opt. Instrum. Eng. 210, 18 (1980).

Lindgren, E. R.

R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).

Maddux, G. E.

G. E. Maddux, S. L. Moorman, R. R. Corwin, Air Force Flight Dynamics Laboratory report AFFDL-TM-78-109-FBE (1978).

Meynart, R.

R. Meynart, Rev. Sci. Instrum. 53, 110 (1982).
[CrossRef]

R. Meynart, Rev. Phys. Appl. 17, 301 (1982).
[CrossRef]

R. Meynart, Appl. Opt. 19, 1385 (1980) and references contained therein.
[CrossRef] [PubMed]

Moorman, S. L.

G. E. Maddux, S. L. Moorman, R. R. Corwin, Air Force Flight Dynamics Laboratory report AFFDL-TM-78-109-FBE (1978).

Oppenheim, A.

A. Oppenheim, R. Schafer, Digital Signal Processing (Prentice-Hall, Englewood Cliffs, N.J., 1975).

Pugh, D. J.

G. H. Kaufmann, A. E. Ennos, B. Gale, D. J. Pugh, J. Phys. E 13, 579 (1980).
[CrossRef]

Schafer, R.

A. Oppenheim, R. Schafer, Digital Signal Processing (Prentice-Hall, Englewood Cliffs, N.J., 1975).

Simpkins, P. G.

P. G. Simpkins, T. Dudderar, J. Fluid Mech. 89, 665 (1978).
[CrossRef]

Yoo, J. K.

R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).

Appl. Opt. (2)

J. Fluid Mech. (1)

P. G. Simpkins, T. Dudderar, J. Fluid Mech. 89, 665 (1978).
[CrossRef]

J. Phys. E (2)

D. E. Fitzjarrald, J. Phys. E 15, 911 (1982).
[CrossRef]

G. H. Kaufmann, A. E. Ennos, B. Gale, D. J. Pugh, J. Phys. E 13, 579 (1980).
[CrossRef]

Phys. Fluids (1)

P. E. Dimotakis, F. D. Debussy, M. M. Koochesfahani, Phys. Fluids 24, 995 (1981).
[CrossRef]

Proc. Soc. Photo-Opt. Instrum. Eng. (1)

H. Kreitlow, T. Kreis, Proc. Soc. Photo-Opt. Instrum. Eng. 210, 18 (1980).

Rev. Phys. Appl. (1)

R. Meynart, Rev. Phys. Appl. 17, 301 (1982).
[CrossRef]

Rev. Sci. Instrum. (2)

R. E. Elkins, G. R. Jackman, R. R. Johnson, E. R. Lindgren, J. K. Yoo, Rev. Sci. Instrum. 48, 7, 738 (1977).

R. Meynart, Rev. Sci. Instrum. 53, 110 (1982).
[CrossRef]

Other (2)

G. E. Maddux, S. L. Moorman, R. R. Corwin, Air Force Flight Dynamics Laboratory report AFFDL-TM-78-109-FBE (1978).

A. Oppenheim, R. Schafer, Digital Signal Processing (Prentice-Hall, Englewood Cliffs, N.J., 1975).

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Figures (8)

Fig. 1
Fig. 1

Experimental setup: A, air flow; G, aerosol generator; B, beam from double-pulsed ruby laser; L1, spherical lens; L2, cylindrical lens; L3, camera lens.

Fig. 2
Fig. 2

Double-exposure photograph of pairing event.

Fig. 3
Fig. 3

Image processing system: L1,L2, lenses for beam size adjustment; P, photograph; L3, Fourier transform lens; F, Fourier plane with stop for undiffracted beam; C, video camera; A/D, video interface.

Fig. 4
Fig. 4

Photographs (negative print) of TV monitor showing an example of processed image. (A) Center, I(m,n) intensity distribution of Young’s fringes oriented at~18° with respect to the vertical axis; top left, averaged line f(m) 0 ≤ m ≤ 127; bottom left, |FFT f(m)| (80 points of a 256-point FFT); top right, logf(m); bottom right, |FFT logf(m)|. (B) See caption of (A); top right, k(m) = sin2(πm/127) · [logf(m)]; bottom right, |FFT k(m)|.

Fig. 5
Fig. 5

Photograph of TV monitor for same fringes as in Fig. 4 processed by the autocorrelation technique. Top left, averaged autocorrelation g(u) 0 ≤ u ≤ 127; bottom left, FFT g(u) (80 points of a 256-point FFT); top right, g′(u) = g(u)/(1 + exp − u2/p2) where p is an adjustable parameter; bottom right, |FFT g′(u)|.

Fig. 6
Fig. 6

(A) In-plane velocity field of interacting vortices. (B) Velocity field obtained after subtraction of constant velocity (0.81 Ue) along the x axis.

Fig. 7
Fig. 7

Spatial filter: L1,L2, beam expander; P, photograph; FP, Fourier plane with filtering hole; L3,L4, transform lenses (focal length: f); I, image plane.

Fig. 8
Fig. 8

Example of filtered image Δυx = 1.09 m/sec. (A) Flow contours and numeration of fringes observed in (B) and (C). (B) Photograph (positive print) of TV monitor showing the optically filtered image after digital contrast enhancement; note that the tiny vertical lines in the isovelocity fringes are due to the TV monitor. (C) Photograph of TV monitor showing the isovelocity fringes after digital low-pass filtering of the image in (B) and further contrast enhancement.

Equations (4)

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f ( m ) = n = 0 127 I [ m + ( n 63 ) tan α , n ] 0 m 127
g ( u ) = n = 0 127 { m [ I ( m , n ) I ( m + u , n ) ] m [ I ( m , n ) ] 2 } 127 u 127.
g ( u ) = g ( u ) / [ 1 + exp ( u 2 / p 2 ) ] ,
I ( m , n ) = 0 I ( m , n ) I min = 255 [ I ( m , n ) I min ] / ( I max I min ) = 255 I ( m , n ) I max , I min I ( m , n ) I max

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