Quantitative analysis by digital processing of streakline flow visualization images
Abstract
An experimental technique is described for the quantitative analysis of smoke filament (streakline) flow visualization images. The streakline, smoke droplets emitted by a point source, is illuminated by a sheet of laser light. The 1-2 micron diameter droplets trace the diffusive motions in the flow. Fast photography is performed to record the streaklines using ASA 400 film (an 800 ASA film system is under development). The film frames are scanned by a video camera linked to a mainframe (PDP 11-34) computer to digitize the images within a 256 x 256 pixel grid with 256 gray levels. Sample results are provided from a study of the entrained mixing layer of two plane parallel flows at speeds of 2 and 1 m/sec, respectively. The photography was performed at 600 frames/sec with 1/3000 sec exposures, yielding a spatial resolution of 1.5 mm. The method furnishes data for calculating the probability distribution for the presence of an oil droplet at any point of the flow, as well as recording the turbulent structures which form. Correlations between the vertical displacements of the droplets and the longitudinal speed of the flow permit calculating the frequency of passage of the vortices.
- Publication:
-
Academie des Sciences Paris Comptes Rendus Serie Sciences Mathematiques
- Pub Date:
- January 1986
- Bibcode:
- 1986CRASM.302..151B
- Keywords:
-
- Numerical Flow Visualization;
- Smoke;
- Turbulent Flow;
- Data Acquisition;
- Entrainment;
- Filaments;
- Mixing;
- Mixing Layers (Fluids);
- Vortices;
- Fluid Mechanics and Heat Transfer