Largescale tomographic PIV in forced and mixed convection using a parallel SMART version
 Matthias Kühn,
 Klaus Ehrenfried,
 Johannes Bosbach,
 Claus Wagner
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Largescale tomographic particle image velocimetry (tomographic PIV) was used to study largescale flow structures of turbulent convective air flow in an elongated rectangular convection cell. Three flow cases have been investigated, that is, pure forced convection and mixed convection at two different Archimedes numbers. The Reynolds number was constant at Re = 1.04 × 10^{4} for all cases, while the Archimedes numbers were Ar = 2.1 and 3.6 for the mixed convection cases, corresponding to Rayleigh numbers of Ra = 1.6 × 10^{8} and 2.8 × 10^{8}, respectively. In these investigations, the size of the measurement volume was as large as 840 mm × 500 mm × 240 mm. To allow for statistical analysis of the measured instantaneous flow fields, a large number of samples needed to be evaluated. Therefore, an efficient parallel implementation of the tomographic PIV algorithm was developed, which is based on a version of the simultaneous multiplicative reconstruction technique (SMART). Our algorithm distinguishes itself amongst other features by the fact that it does not store any weighting coefficients. The measurement of forced convection reveals an almost twodimensional roll structure, which is orientated in the longitudinal cell direction. Its mean velocity field exhibits a core line with a wavy shape and a wavelength, which corresponds to the height and depth of the cell. In the instantaneous fields, the core line oscillates around its mean position. Under the influence of thermal buoyancy forces, the global structure of the flow field changes significantly. At lower Archimedes numbers, the resulting rolllike structure is shifted and deformed as compared to pure forced convection. Additionally, the core line oscillates much more strongly around its mean position due to the interaction of the roll structure with the rising hot air. If the Archimedes number is further increased, the rolllike structure breaks up into four counterrotating convection rolls as a result of the increased influence of buoyancy forces. Moreover, largescale tomographic PIV reveals that the orientation of these rolls reflects a ‘W’like shape in the horizontal X–Zplane of the convection cell.
 Title
 Largescale tomographic PIV in forced and mixed convection using a parallel SMART version
 Journal

Experiments in Fluids
Volume 53, Issue 1 , pp 91103
 Cover Date
 201207
 DOI
 10.1007/s0034801213019
 Print ISSN
 07234864
 Online ISSN
 14321114
 Publisher
 SpringerVerlag
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 Authors

 Matthias Kühn ^{(1)}
 Klaus Ehrenfried ^{(1)}
 Johannes Bosbach ^{(1)}
 Claus Wagner ^{(1)}
 Author Affiliations

 1. Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstraße 10, 37073, Göttingen, Germany