Investigation of a turbulent spot and a tripped turbulent boundary layer flow using time-resolved tomographic PIV

Investigation of a turbulent spot and a tripped turbulent boundary layer flow using time-resolved... In this feasibility study the tomographic PIV technique has been applied to time resolved PIV recordings for the study of the growth of a turbulent spot in a laminar flat plate boundary layer and to visualize the topology of coherent flow structures within a tripped turbulent flat plate boundary layer flow. The experiments are performed around (Re x )1/2 ≈ 450 in a low speed wind-tunnel using four high speed CMOS cameras operating up to 5 kHz. The volume illumination required a multiple-reflection system able to intensify light intensity within the measurement volume. This aspect is deemed essential when a high-speed tomographic PIV system is applied in air flows. The particle image recordings are used for a three dimensional tomographic reconstruction of the light intensity distribution within the illuminated volume. Each pair of reconstructed three-dimensional light distributions is analyzed by 3D spatial cross-correlation using iterative multi-grid schemes with volume-deformation, yielding a correlated time sequence of three-dimensional instantaneous velocity vector volumes. The coherent structures organization is analyzed by 3D-vorticity and -swirling-strength iso-surfaces visualization. In both flow types streaks and hairpin-like or arch vortical structures are most prominent. The data gives insight into the role of these structures for the spatio-temporal arrangement of the wall normal flow exchange mechanisms, especially of the instantaneous Reynolds stress events Q2 and Q4. A description of different self-sustainable flow organizations based on modifications of the hairpin-vortex- and streak-models is given. Two preliminary results are essential: Self-sustainability of a coherent vortical structure depends on the ability to entrain high momentum fluid, initially Q4. And, stream-wise swirl at the near-wall region of arch or hairpin-like vortices has been observed to be rare. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experiments in Fluids Springer Journals

Investigation of a turbulent spot and a tripped turbulent boundary layer flow using time-resolved tomographic PIV

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Publisher
Springer-Verlag
Copyright
Copyright © 2007 by Springer-Verlag
Subject
Engineering; Engineering Fluid Dynamics; Fluid- and Aerodynamics; Engineering Thermodynamics, Heat and Mass Transfer
ISSN
0723-4864
eISSN
1432-1114
D.O.I.
10.1007/s00348-007-0403-2
Publisher site
See Article on Publisher Site

Abstract

In this feasibility study the tomographic PIV technique has been applied to time resolved PIV recordings for the study of the growth of a turbulent spot in a laminar flat plate boundary layer and to visualize the topology of coherent flow structures within a tripped turbulent flat plate boundary layer flow. The experiments are performed around (Re x )1/2 ≈ 450 in a low speed wind-tunnel using four high speed CMOS cameras operating up to 5 kHz. The volume illumination required a multiple-reflection system able to intensify light intensity within the measurement volume. This aspect is deemed essential when a high-speed tomographic PIV system is applied in air flows. The particle image recordings are used for a three dimensional tomographic reconstruction of the light intensity distribution within the illuminated volume. Each pair of reconstructed three-dimensional light distributions is analyzed by 3D spatial cross-correlation using iterative multi-grid schemes with volume-deformation, yielding a correlated time sequence of three-dimensional instantaneous velocity vector volumes. The coherent structures organization is analyzed by 3D-vorticity and -swirling-strength iso-surfaces visualization. In both flow types streaks and hairpin-like or arch vortical structures are most prominent. The data gives insight into the role of these structures for the spatio-temporal arrangement of the wall normal flow exchange mechanisms, especially of the instantaneous Reynolds stress events Q2 and Q4. A description of different self-sustainable flow organizations based on modifications of the hairpin-vortex- and streak-models is given. Two preliminary results are essential: Self-sustainability of a coherent vortical structure depends on the ability to entrain high momentum fluid, initially Q4. And, stream-wise swirl at the near-wall region of arch or hairpin-like vortices has been observed to be rare.

Journal

Experiments in FluidsSpringer Journals

Published: Oct 13, 2007

References

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