Statistics of turbulent structures in a thermal plasma jet

The number, size, location and velocity of turbulent structures in an argon plasma jet were experimentally investigated using a fast-shutter CCD camera. The camera yielded sequences of plasma jet images with a time interval of 11 μs, and the turbulent structures in the jet were identified by subtraction of matrices representing the succeeding images in the series. This method reveals the regions characterized by increasing or decreasing luminosity that move along the plasma flow and reflect high energy and mass transport in these areas. The results show a high diversity of measured quantities characterizing these structures, and the evaluation thus required the involvement of statistical methods. The statistical distributions of the structure velocities change from non-Gaussian to Gaussian-like ones, depending on the gas flow rate, and so indicate the transitions from a turbulent flow characterized by a relatively regular structure generation to more developed turbulence