Decay laws, anisotropy and cyclone-anticyclone asymmetry in decaying rotating turbulence

Moisy, F., Morize, C., Rabaud, M. & Sommeria, J.

Journal of Fluid Mechanics, vol. 666 (2011), pp. 5-35

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Movie 1. Experimental setup, seen from the rotating frame. The first sequence shows the water channel, 4 m wide, 9 m long and 1 m thickness, mounted on the 13-m-diameter rotating platform. The second sequence shows the grid, translated at constant velocity V_g = 0.3 m/s along the channel (Reynolds number Re_g = 42 000). The horizontal green line on the grid marks the intersection with the laser sheet, used for the Particule Image Velocimetry (PIV) measurements in the horizontal plane. The free surface disturbances in the wake of the grid are essentially damped when PIV measurements are performed.Download movie.

Movie 2. Vertical vorticity ω_z measured in an horizontal plane (y,x) at mid-height, for a rotation rate of Ω = 0.20 rad/s (T = 30 s). The background rotation is anticlockwise. Positive vorticity (in red) is cyclonic, and negative vorticity (in blue) is anticyclonic. The sampling rate is not constant: the delay between two images is increased in 4 steps, from 2 s to 20 s. At small time a strong inertial wave (anticyclonic circular translation, of period T / 2 = 15 s) advects the turbulent flow. At intermediate time (t ≈ 400 s), well defined cyclonic vortices emerge. Note the pairing of two cyclones at t ≈ 1000 s. At large time, t ≈ 3000 s, the vorticity field is dominated by small scale symmetric fluctuations advected by the large scale horizontal motion.Download movie.

Movie 3. Spanwise vorticity ω_y measured in the vertical plane (x,z), for a rotation rate Ω = 0.20 rad/s (T = 30 s), showing the growth of anisotropy and the gradual formation of vertical layers. The grid is translated from left to right, and crosses the center of the imaged area at t = 0. The sampling rate is not constant: the delay between two images is increased in 4 steps, from 2 s to 20 s. Due to the horizontal flow induced by the inertial wave, the structures quickly enter and leave the vertical plane. Download movie.