Abstract
Simultaneous dual-plane PIV experiments, which utilized three cameras to measure velocity components in two differentially separated planes, were performed in streamwise-spanwise planes in the log region of a turbulent boundary layer at a moderate Reynolds number (Reτ ∼ 1100). Stereoscopic data were obtained in one plane with two cameras, and standard PIV data were obtained in the other with a single camera. The scattered light from the two planes was separated onto respective cameras by using orthogonal polarizations. The acquired datasets were used in tandem with continuity to compute all 9 velocity gradients, the complete vorticity vector and other invariant quantities. These derived quantities were employed to analyze and interpret the structural characteristics and features of the boundary layer. Sample results of the vorticity vector are consistent with the presence of hairpin-shaped vortices inclined downstream along the streamwise direction. These vortices envelop low speed zones and generate Reynolds shear stress that enhances turbulence production. Computation of inclination angles of individual eddy cores using the vorticity vector suggests that the most probable inclination angle is 35° to the streamwise-spanwise plane with a resulting projected eddy inclination of 43° in the streamwise-wall-normal plane.
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Notes
This is consistent with Brodkey et al. (1973) who provided an interpretation of production, based on instantaneous Reynolds shear stress and instantaneous wall-normal gradient, where the production term almost exactly balances dissipation. Other definitions have also been proposed (see Bradshaw 1974).
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Acknowledgements
The authors gratefully acknowledge support from the National Science Foundation through Grants ACI-9982274, CTS-9983933 and CTS-0324898, the Graduate School of University of Minnesota and the David and Lucile Packard Foundation. We are indebted to Dr. Nicholas Hutchins, William Hambleton and Aizaz Bhuiyan for their help in data acquisition and many discussions during the course of this study.
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Ganapathisubramani, B., Longmire, E.K., Marusic, I. et al. Dual-plane PIV technique to determine the complete velocity gradient tensor in a turbulent boundary layer. Exp Fluids 39, 222–231 (2005). https://doi.org/10.1007/s00348-005-1019-z
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DOI: https://doi.org/10.1007/s00348-005-1019-z