Modelling Study to Compare the Flow and Heat Transfer Characteristics of Low-Power Hydrogen, Nitrogen and Argon Arc-Heated Thrusters

摘要

A modelling study is performed to compare the plasma flow and heat transfer characteristicsof low-power arc-heated thrusters (arcjets) for three different propellants: hydrogen,nitrogen and argon.The all-speed SIMPLE algorithm is employed to solve the governing equations,which take into account the effects of compressibility,Lorentz force and Joule heating,aswell as the temperature- and pressure-dependence of the gas properties.The temperature,velocityand Mach number distributions calculated within the thruster nozzle obtained with differentpropellant gases are compared for the same thruster structure,dimensions,inlet-gas stagnantpressure and arc currents.The temperature distributions in the solid region of the anode-nozzlewall are also given.It is found that the flow and energy conversion processes in the thrusternozzle show many similar features for all three propellants.For example,the propellant is heatedmainly in the near-cathode and constrictor region,with the highest plasma temperature appearingnear the cathode tip; the flow transition from the subsonic to supersonic regime occurs withinthe constrictor region; the highest axial velocity appears inside the nozzle; and most of the inputpropellant flows towards the thruster exit through the cooler gas region near the anode-nozzlewall.However,since the properties of hydrogen,nitrogen and argon,especially their molecularweights,specific enthalpies and thermal conductivities,are different,there are appreciable differencesin arcjet performance.For example,compared to the other two propellants,the hydrogenarcjet thruster shows a higher plasma temperature in the arc region,and higher axial velocitybut lower temperature at the thruster exit.Correspondingly,the hydrogen arcjet thruster has thehighest specific impulse and arc voltage for the same inlet stagnant pressure and arc current.Thepredictions of the modelling are compared favourably with available experimental results.