Image processing of hydrogen-bubble flow visualization for quantitative evaluation of hairpin-type vortices as a flow structure of turbulent boundary layers
This study uses time-dependent velocity-profile data established from image processing of hydrogen-bubble flow-visualization data for both a turbulent boundary layer and experimentally synthesized hairpin vortices. The data are first employed to examine the characteristics of the velocity and velocity-derived properties for the two flow cases (e.g., u{prime}, du/dy, d{sup 2}u/dy{sup 2}, du/dt, and VITA). The hairpin-vortex velocity patterns are then employed as reference patterns to search for comparable vortex structures in the wall region of a turbulent boundary layer using a template-matching, pattern-recognition technique. Basically, it is determined that use of two-dimensional (y,t) velocity data in conjunction with the original visualization sequence is much more effective in establishing temporal and spatial bursting characteristics for a turbulent boundary layer. Results indicate that the velocity properties of VITA-detected burst events are strikingly similar to detected hairpin-like events. The general velocity behavior of both hairpin vortices and VITA-detected bursting events is characterized by hump-shaped velocity contours, a sharp deficit-to-excess interface in velocity fluctuation contours, and localized vorticity concentrations.
- Research Organization:
- Lehigh Univ., Bethlehem, PA (USA)
- OSTI ID:
- 6970893
- Country of Publication:
- United States
- Language:
- English
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