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Control of turbulence with a high degree-of-freedom active grid

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This abstract describes a significant advance in the technology used to generate turbulence in wind tunnels. We present a new active grid with many degrees of freedom, and demonstrate its ability to control the correlation length of the turbulent fluctuations it produced in a wind tunnel. The paddles of previous active grids were constrained to move together in rows and columns, meaning that the motions of the paddles were correlated across the full width and height of the tunnel. These motions, which were usually random, produced relatively intense turbulent fluctuations. In our grid, each of 129 paddles’ positions could be moved independently with separate position-controlled servomotors. Because of this, we could introduce desired correlations between the motions of the paddles, by encoding them in the algorithm that set the paddle positions. We found that by changing the extent of the correlations between nearby paddles, we could control the spatial extent of the correlations in the turbulent fluctuations.

Author(s):

Gregory Bewley    
Max Planck Institute for Dynamics and Self-Organization
Germany

Johannes Kassel    
Max Planck Institute for Dynamics and Self-Organization
Germany

Eberhard Bodenschatz    
Max Planck Institute for Dynamics and Self-Organization
Germany