ABSTRACT
The fluid dynamic behavior of an atmospheric pressure plasma jet emanating from a plasma spray torch has been characterized using various diagnostics and modeling. The diagnostic methods include LDA, electric and acoustic probing, emission spectroscopy and enthalpy probes, and the measured quantities are mean velocity profiles in the jet, turbulence intensity profiles, temperature profiles, and correlations between arc voltage fluctuations and light fluctuations as well as acoustical emissions from the jet. The results show that the transition to turbulence of the jet core leads to entrainment of cold gas bubbles which mix very slowly with the hot gas. The velocity fluctuations are non-isotropic, and the correlation of electric, acoustic and light fluctuations demonstrate that the turbulence fluctuations may be affected by arc motion inside the nozzle. The voltage fluctuations at definite frequencies indicate that the arc operates in a restrike mode. These characterizations indicate the need for improved control of the fluid dynamic behavior of the plasma jet in order to improve the reproducibility of plasma sprayed coatings.
