scart.dlr.de>Research Projects
Friday, 14. December 2018
 

Tomographic-Thermochromic-Liquid-Crystal-Particle-Image-Velocimetry

For extended deeper physical insight in buoyancy driven flows it is important to measure simultaneously the three-dimensional temperature and velocity fieldIn the future, such a technique could be applied in industrial measurements of cabin flows with the objective to improve the ventilation efficiency and the passenger comfort.

Tomographic particle image velocimetry (Tomo-PIV) is a non-intrusive technique which allows measurements of three-dimensional instantaneous velocity fields. So far, the technique has been mainly been applied to rather small measurement volumes. Though recently, the measurement volume was increased to volumes of the order of one cubic meter by using helium-filled soap bubbles as tracer particles in an airflow (see Kühn et al. 2011).

In addition, there is a technique called Particle Image Thermography (PIT) which allows to measure temperature fields as well. Thereby, Thermochromic-Liquid-Crystals (TLCs) are used as tracer particles, because they are able to provide – after calibration – the local fluid temperature. This is possible due to the a wavelength-reflection of these particles which depends on the crystal-temperature.

With this project, the PIT and Tomo-PIV will be coupled with the objective to measure turbulent Rayleigh-Bénard convection in water. To do this, a cubic cell with a side length of 0.5m was built. So far we conducted a Tomo-PIV measurement and obtained the instantaneous 3D-3C velocity fields. In Fig. 1, the time-averaged velocity field is shown. The large-scale circulation (LSC) was clearly reconstructed.

Fig 1: The corresponding time-averaged velocity field of a Tomogaphic-PIV evaluation showing the LSC at Ra = 1.0 x 10e10, Pr=6.9
Fig 2: Unfiltered image of TLC tracer particles in the cubic cell. The colour play is clearly visible

References:

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:

Dr. rer. nat. Daniel Schiepel 
German Aerospace Center (DLR)
Institute of Aerodynamics and Flow Technology, Department Ground Vehicles
Göttingen
Phone: +49 551 709-2652

 
German Aerospace Center (DLR), Institute of Aerodynamics and Flow Technology, SCART
Bunsenstraße 10, 37075 Göttingen, Germany