Experimental study of turbulent thermal diffusion in oscillating grids turbulence

We have experimentally detected a new effect, turbulent thermal diffusion, as predicted theoretically by Elperin et al. (Phys Rev Lett (1996) 76:224-228) and associated with the turbulent transport of inertial particles. The essence of this effect is an appearance of a non-diffusive mean flux of particles in the direction of the mean heat flux. This results in formation of large-scale inhomogeneities in the spatial distribution of inertial particles that are accumulated in regions of minimum mean temperature in the surrounding fluid. The experiments were performed in oscillating grids turbulence with an imposed mean temperature gradient. We used Particle Image Velocimetry to determine the turbulent velocity field, and an Image Processing Technique based on the analysis of the intensity of the Mie scattering to determine the spatial distribution of tracer particles. Analysis of the intensity of laser light Mie scattering by tracer particles showed that the tracer particles accumulate in the vicinity of the minimum of the mean temperature. The latter finding confirms the existence of the effect of turbulent thermal diffusion.