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Friday, 14. December 2018
 

Large-scale tomographic particle image velocimetry

Tomographic particle image velocimetry (tomographic PIV or Tomo-PIV) is a new PIV technique which allows for measurements of three-dimensional instantaneous flow fields in a complete volume (see Elsinga et al. 2006). Up to now, this technique has been applied to rather small measurement volumes of the order of only a few cubic centimeters with a very high spatial resolution, particularly for investigations of the three-dimensional structures in turbulent flows.

To measure large-scale flow structures in thermal convective air flows, a tomographic PIV system for measurement volumes of the order of one cubic meter and a spatial resolution of some centimeter employing helium-filled soap bubbles as tracer particles was developed (see Kühn et al. 2011). The system was first applied to the flow in a long rectangular convection cell with a size of 2.5m x 0.5m x 0.5m (see Fig. 1). Forced convection at a Reynolds number of 530 (based on the height of the inlet channel and the average inlet velocity) was investigated. The size of the measurement volume and the interrogation volumes amount to 750mm x 450mm x 165mm and 48mm x 48mm x 24mm, respectively. The mean flow field exhibits an almost two-dimensional roll structure with a rotation axis in cell length direction (see Fig. 1). However, the instantaneous flow fields are rather three-dimensional as can be seen in Fig. 2. A roll-like structure can still be detected but its core line oscillates around its mean position.

Figure 1: Mean flow field in the long rectangular convection cell as measured with the large-scale tomographic PIV system. The size of the measurement volume amounts to 750mm x 450mm x 165mm. The magnitude of the measured velocity in five different planes is shown using a color code.
Figure 2: Snapshots of three instantaneous flow fields as measured with the large-scale tomographic PIV system. The flow field is visualized by iso-surfaces of the velocity magnitude (orange corresponds to 0.115m/s, green to 0.090m/s and blue to 0.040m/s). The upper flow field is captured at time t0, the middle at t0 + 13.5s and the lower at t0 + 25.5s.

References:

Elsinga GE, Scarano F, Wieneke B, van Oudheusden BW (2006) Tomographic particle image velocimetry. Exp Fluids 41:933-947

Kühn M, Ehrenfried K, Bosbach J, Wagner C (2011) Large-scale tomographic particle image velocimetry using helium-filled soap bubbles. Exp Fluids 50:929-948

 

Contact:

Michael Mommert
German Aerospace Center (DLR)
Institute of Aerodynamics and Flow Technology, Department Ground Vehicles
Göttingen
Phone: +49 551 709-2869

 
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