Effects of constrictor geometry, arc current, and gas flow rate on thermal plasma characteristics in a segmented arc heater

A numerical simulation on a segmented arc heater which is used to generate high thermal flow environments for the test of heat shield materials, were carried out. In this numerical prediction work, targets level of input power class, minimum enthalpy at the exit of the heater, and maximum pressure inside the heater were set up as 400 kW, 20 MJ/kg, and 4 bar, respectively. In order to produce uniform temperature and velocity characteristics of thermal flow for a successful test, effects of design and operation variables on the thermal plasma characteristics were analyzed. Number of the segments packs and diameter of the constrictor were changed 1 ~ 3 (105 ~ 315 mm) and 12 ~ 20 mm, respectively. As the torch operating variables, arc current was changed from 300 A to 500 A and plasma forming gas flow rate was varied from 6 g/s to 14 g/s. Arc current was adjusted to achieve about 400 kW according to constrictor geometry at fixed gas flow rate of 10 g/s, and optimal design conditions for uniform radial temperature and low pressure profiles with Mach number 1 at the supersonic throat were expected when the constrictor length and diameter were 315 mm and 16 mm, respectively. From the numerical results, diameters of the supersonic nozzle exit which determines test target size were calculated as 55.5 mm and 82.4 mm in the cases of Mach number 2 and 3, respectively.