No abstract

The behavior of plasma flow, generated by a D.C. plasma spraying gun, is simulated in a time-dependent 3 D. design. The high-temperature and high-velocity plasma plume is generated by a simple model based on Joule effect. The criterion of validation is the thermal efficiency while the only adjustment parameter is the length of the plasma column inside the anode. The transient plasma flow issuing in air atmosphere is reproduced. The plasma behavior is quite similar to that observed by fast-image video. Moreover, the centerline plasma plume properties are in agreement with experiment measurements, especially close to the torch exit and downstream the laminar-to-turbulent transition.Keywords Thermal plasma Á Unsteady Á Modeling Á Heat and acceleration of gas Á Air engulfment Nomenclature S ef Thermal source by Joule effect (W) Q conv Losses by convection (W) ũ Velocity vector (m/s) E Global energy (W) k Thermal conductivity (W/m K) J j Diffusion flux of the j specie (kg/m 2 s) e Turbulent dissipation rate (m 2 /s 3 ) u i Velocity component along direction i (m/s) G k Dynamic viscosity (kg/m s) U Average arc voltage (V) L m Average plasma column length (m) V 1 First heating zone volume (m 3 ) P 1 Electrical power generated in V 1 volume (W) l 1 Constant length of the heating zone V 1 (m) c Rotating angle of the V 2 area (degree) f Frequency of the arc voltage fluctuation (hz) l min Shortest global heating zone length (m) p Pressure (Pa) Q rad Losses by radiation (W) q Density (kg/m 3 ) T Temperature (K) h j Specific enthalpy of the j specie (J/kg) s eff Á ũ Viscous dissipation term (W/m 2 ) j Turbulent kinetic energy (m 2 /s 3 ) g i Gravitation vector component along the i direction G bTurbulence production rate due to natural convection bConstant for k-e model r e PRANDTL turbulent number for e l t Turbulent viscosity (kg/m s) P m Average input power (W) I Arc current intensity (A) g Thermal efficiency rate (%) V 2 Second heating zone volume (m 3 ) P 2 Electrical power generated in V 2 volume (W) l 2 (t)Time-dependent length of the heating zone V 2 (m) V(t) Time-dependent arc voltage (V) a Constant angle of the truncated cornet of the V 2 area (degree) l max Longest global heating zone length (m)