Microscopic digital Holographic PIV is used to measure the 3D velocity distributions in the roughness sublayer of a turbulent boundary layer over a rough wall. The sample volume extends from the surface, including the space between the tightly packed, 0.45 mm high, pyramidal roughness elements, up to about 5 roughness heights away from the wall. To facilitate observations though a rough surface, experiments are performed in a facility containing fluid that has the same optical refractive index as the acrylic rough walls. Magnified in line holograms are recorded on a 4864×3248 pixel camera at a resolution of 0.67μm/pixel. The flow field is seeded with 2μm silver coated glass particles, which are injected upstream of the same volume. A multiple-step particle tracking procedure is used for matching the particle pairs. In recently obtained data, we have typically matched ∼5000 particle images per hologram pair. The resulting unstructured 3D vectors are projected onto a uniform grid with spacing of 60 μm in all three directions in a 3.2×1.8×1.8 mm sample volume. The paper provides sample data showing that the flow in the roughness sublayer is dominated by slightly inclined, quasi-streamwise vortices whose coherence is particularly evident close to the top of the roughness elements.
- Fluids Engineering Division
Three Dimensional Volumetric Velocity Measurements in the Inner Part of a Turbulent Boundary Layer Over a Rough Wall Using Digital HPIV
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Talapatra, S, & Katz, J. "Three Dimensional Volumetric Velocity Measurements in the Inner Part of a Turbulent Boundary Layer Over a Rough Wall Using Digital HPIV." Proceedings of the ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting: Volume 2, Fora. Montreal, Quebec, Canada. August 1–5, 2010. pp. 193-201. ASME. https://doi.org/10.1115/FEDSM-ICNMM2010-30813
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