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 tomographic PIV

Schröder, A.
Geisler, R.
Elsinga, G.E.
Scarano, F.
Dierksheide, U.

Aerospace Engineering

Aerospace Design, Integration and Operations

2007-10-13

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://resolver.tudelft.nl/uuid:aee7a88f-72cc-4d2d-b3de-164c7448c5dc

Springer

1432-1114

Experiments in Fluids, 44 (2), 2008

Institutional Repository

journal article

(c) 2007 The Authors; Springer