Some experimental results on velocity and vorticity measurements in turbulent grid flows with controlled sign of mean helicity

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Abstract
We present results of experiments on turbulent grid flow in the salt water tunnel of the Laboratory for Vorticity-Helicity Studies, Faculty of Engineering, Tel Aviv University. The experiments include measurements of the longitudinal components of velocity and vorticity. This was made by a probe consisting of a seven-electrode probe, allowing to perform absolute measurements of ?1, assembled together with a commercial hot film probe. The main bulk of measurements was made past a grid with a circular mesh. This was necessary to perform experiments with controlled sign of mean helicity of the turbulent fluctuations which was achieved by installing various propellers in the grid holes. The results include mainly various helicity related quantities (mean, spectra, etc.) for grids with propellers producing perturbation clockwise, anticlockwise or both as well as for grid with empty holes. Other results like the ratio are reported. Apart from confirming the phenomenon of symmetry breaking new results about properties of the vorticity field are included.