Liquid-Crystal Particle Image Velocimetry
Many flow properties, e.g. heat transport, depend on the temperature and velocity field. Thus, it is of great interest to acquire both fields simultaneously.
Therefore, the technique of combined Particle Image Thermography (PIT) and Particle Image Velocimetry (PIV) for the simultaneous acquisition of instantaneous temperature and velocity fields, which is well-known in liquids , is adapted for air flows. For this reason, thermochromic liquid crystalline substances (TLCs), which - in a certain temperature range- reveal a temperature-depending reflection of the wavelength under the illumination with white light, are used. Small particles of these liquid crystals are used as tiny thermometers and as tracer particles for the velocimetry.
Newly developed white light sheet optics based on LEDs and new techniques for the particle generation allow for the usage of this measurement technique in air flows.
Recently, a paper called “Simultaneous Measurement of Temperature and Velocity Fields in Convective Air Flows” has been published. It focusses on particle generation as well as on the corresponding illumination and image filtering processes. It also presents results of combined PIV/PIT experiments in a system with continuous air exchange.
This new measurement technique is used for investigations of fundamental physical processes, e.g. the behavior of thermal plumes in Rayleigh-Bénard convection and mixed convection in cuboidal samples, as well as for the research regarding flow phenomena in the interior of an aircraft.
Figure 1 shows the evaluated temperature and velocity field of a warm plume in air which rises fromthe thermal boundary layer above the heated bottom plate of the convection sample.
D. Schmeling, J. Bosbach and C. Wagner: “Simultaneous Measurement of Temperature and Velocity Fields in Convective Air Flows”. Meas. Sci. Technol. 25, (2014) 035302, accepted.
German Aerospace Center (DLR)
Institute of Aerodynamics and Flow Technology, Department Ground Vehicles
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