Time-resolved measurements of coherent structures in the turbulent boundary layer
Time-resolved particle image velocimetry was used to examine the structure and evolution of swirling coherent structure (SCS), one interpretation of which is a marker for a three-dimensional coherent vortex structure, in wall-parallel planes of a turbulent boundary layer with a large field of view, 4.3δ × 2.2δ. Measurements were taken at four different wall-normal locations ranging from y/δ = 0.08–0.48 at a friction Reynolds number, Re τ = 410. The data set yielded statistically converged results over a larger field of view than typically observed in the literature. The method for identifying and tracking swirling coherent structure is discussed, and the resulting trajectories, convection velocities, and lifespan of these structures are analyzed at each wall-normal location. The ability of a model in which the entirety of an individual SCS travels at a single convection velocity, consistent with the attached eddy hypothesis of Townsend (The structure of turbulent shear flows. Cambridge University Press, Cambridge, 1976), to describe the data is investigated. A methodology for determining whether such structures are “attached” or “detached” from the wall is also proposed and used to measure the lifespan and convection velocity distributions of these different structures. SCS were found to persist for longer periods of time further from the wall, particularly those inferred to be “detached” from the wall, which could be tracked for longer than 5 eddy turnover times.
KeywordsVortex Particle Image Velocimetry Coherent Structure Particle Image Velocimetry Measurement Convection Velocity
We would like to acknowledge and thank Prof. Mory Gharib and Dr. David Jeon for their assistance and allowing us to use their free surface water tunnel facility at Caltech in which all the experiments presented were performed. We would also like to gratefully acknowledge the Air Force Office of Scientific Research (AFOSR) for their support of this research under award number #FA9550-09-1-0701. Anonymous reviewers provided recommendations that have significantly improved the quality of this manuscript.
- Bandyopadhyay P, Head MR (1979) Visual investigation of turbulent boundary layer structure. Cambridge University Engng Department of FilmGoogle Scholar
- Bobba KM (2004) Robust flow stability: theory, computations and experiments in near wall turbulence. PhD thesis, California Institute of TechnologyGoogle Scholar
- Elsinga GE, Marusic I (2010) Evolution and lifetimes of flow topology in a turbulent boundary layer. Phys Fluids 015102Google Scholar
- Ganapathisubramani B, Longmire EK, Marusic I (2006) Experimental investigation of vortex properties in a turbulent boundary layer. Phys Fluids 055105Google Scholar
- Hunt JCR, Wray AA, Moin P (1988) Eddies, stream, and convergence zones in turbulent flows. Center for Turbulence Research Report CTR-S 88:193–208Google Scholar
- LeHew JA (2012) Spatio-temporal analysis of the turbulent boundary layer and an investigation of the effects of periodic disturbances. PhD thesis, California Institute of TechnologyGoogle Scholar
- Lozano-Duran A, Flores O, Jiménez J (2012) Three-dimensional structure of momentum transfer in turbulent channels. J Fluid Mech 694:100–130Google Scholar
- Marusic I, McKeon BJ, Monkewitz PA, Nagib HM, Smits AJ, Sreenivasan KR (2010) Wall-bounded turbulent flows at high Reynolds numbers: recent advances and key issues. Phys Fluids 065103Google Scholar
- Theodorsen T (1952) Mechanism of turbulence. In Proceedings of 2nd Midwestern Conference on Fluid Mechanics. Ohio State UniversityGoogle Scholar
- Townsend AA (1976) The structure of turbulent shear flows, 2nd edn. Cambridge University Press, CambridgeGoogle Scholar