Imaging 2D Turbulence

Gravity-driven flow in a soap film tunnel is spatially almost two-dimensional. A modification of particle-image velocimetry technique produces a comprehensive quantitative description of the flow. The technique allows simultaneous acquisition of the velocity (two components) in the plane of the film and the film thickness. The latter behaves as a scalar advected by the flow. The visualization method developed for these data sets uses the thickness field, the vorticity field and the instantaneous velocity streamline pattern for surface elevation, color and bump maps respectively, resulting in color surface images that reveal important features of the flow. In decaying turbulence behind a row of cylinders (2D grid turbulence), the images demonstrate the coarsening of the flow structure with downstream distance, which is the feature specific to turbulence in two dimensions. Strong correlation between thickness fluctuations and vorticity peaks also becomes apparent.