Method and apparatus for determining the direction of motion in multiple exposure velocimetry

• US 4,866,639 A
• Filed: 03/09/1987
• Issued: 09/12/1989
• Est. Priority Date: 03/09/1987
• Status: Expired due to Term

• Current Assignee: University of Illinois
• Original Assignee: University of Illinois
• Inventors: Adrian, Ronald J.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Dixon, Joseph L.
• Application Number:
  US07/023,773
• Time in Patent Office: 918 Days
• Field of Search: 364/560, 364/561, 364/565, 364/550, 364/551, 364/554, 364/555, 364/442, 364/525, 340/703, 340/720, 340/729, 340/794, 340/795, 340/755, 358/88, 358/89, 382/47, 382/48, 73/861.05, 73/861.06, 356/28, 356/27
• US Class Current: 356/28
• CPC Class Codes: G01P 13/045 with speed indication
• CPC Class Codes: G01P 5/001 Full-field flow measurement, e.g. determining flow velocity and direction in a whole region at the same time, flow visualisation

Abstract

The present invention is in the context of the measurement of velocity fields of fluid flows containing many small scattering sites, which exist either in the form of particles or optically activated, discrete fluid volumes. The invention is directed to a method and apparatus for resolving ambiguity with respect to the direction of displacement of particle images recorded by multiple exposures on film or videographic media. The invention enables the elimination of directional ambiguity by means of shifting the image field between exposures by an amount that is greater than any negative displacement occurring in the image field. In this way, all recorded displacements are positive, and negative displacements are obtained from the measurements by mathematically subtracting the artificial shift after the measurements.

Claims

1. In a velocimetry system in which photographic images, involving first and subsequent exposures, are created by accurately times pulses of light from a light source, and multiple particle images displaced by the motion of a fluid are recorded, such that the fluid velocity is inferred from the displacement of the image field between exposure, the improvement which comprises:

means for determining unambiguously the direction of displacement, and hence velocity in said system, said means including means for shifting successive particle images of each scattering site with respect to the first image so that all image displacements are positive even through physical displacements of the scatterers may be negative, said means for shifting being operative during the photographic process between the first exposure and subsequent exposures.

2. A system as defined in claim 1, in which said means for image shifting comprises a rotating mirror.

3. A system as defined in claim 2, in which second images are displaced in the image plane by a constant amount X_s and subsequent images are shifted by amounts proportional to the time lapse since the first image exposure.

4. In a velocimetry method in which images are created by accurately timed pulses of light from a light source, and multiple particle images displaced by the motion of a fluid are recorded, such that the fluid velocity is inferred from the displacement of the image field between exposures, the improvement which comprises:

the step of determining unambiguously the direction of displacement, and hence velocity, in such system, said step including shifting successive images of each scattering site with respect to the first image so that all image displacements are positive even though physical displacements of the scatterers may be negative.

5. A method as defined in claim 4 in which said step is carried out during the photographic process between the first exposure and subsequent exposures.

6. A method as defined in claim 5, in which second images are displaced in the image plane by a constant amount of X_s, and subsequent images are shifted by amounts proportional to the time lapse since the first image exposure.

7. A velocimetry system for measuring fluid velocity, such system comprising:

a light source;

means for recording multiple particle images displaced by the motion of the fluid, said images being created by accurately timed pulses of light from said light source, such that fluid velocity is inferred from the displacement of the image field between exposures, and

means for determining unambiguously the direction of displacement, said means including means for shifting successive images so that all image displacements are positive, said means for shifting being operative during the photographic process between the first exposure and subsequent exposures.

8. A system as defined in claim 7 in which all second images are displaced in the image plane by a constant amount Xs and subsequent images are shifted by amounts proportional to the time lapse since the first image exposure.