Measuring Unsteady Velocity Profiles and Integral Parameters Using Digital Image Processing of Hydrogen Bubble Timelines

Abstract

To aid in the investigation of artificially generated turbulent spots a technique was developed to make instantaneous measurements of full velocity profiles in an unsteady water boundary layer. These profiles were used to document the unsteady behavior of scalar descriptors such as the displacement thickness. The classical hydrogen bubble flow visualization technique was augmented to yield quantitative information by incorporating digital image processing of videotaped boundary layer flow. Digital images were converted into velocity fields using a corrected time-of-flight technique. The capability and limitations of this method in both steady and unsteady flows have been verified using an analytical uncertainty analysis and through comparison with laser-Doppler anemometry measurements. Recommendations are made for effective use of this technique.