The microplasma thruster (MPT) concept is a simple extension of a cold gas micronozzle propulsion device, where a direct-current microdischarge is used to preheat the gas stream to improve the specific impulse of the device. Here we study a prototypical MPT device using a detailed, self-consistently coupled plasma and flow computational model. The model describes the microdischarge power deposition, plasma dynamics, gas-phase chemical kinetics, coupling of the plasma phenomena with high-speed flow, and overall propulsion system performance. Compared to a cold gas micronozzle, a significant increase in specific impulse is obtained from the power deposition in the diverging section of the MPT nozzle. For a discharge voltage of 750 V, a power input of 650 mW, and an argon mass flow rate of 5 SCCM (SCCM denotes cubic centimeter per minute at STP), the specific impulse of the device is increased by a factor of ∼1.5 to about 74 s. The microdischarge remains mostly confined inside the micronozzle and operates in an abnormal glow discharge regime. Gas heating, primarily due to ion Joule heating, is found to have a strong influence on the overall discharge behavior. The study provides a validation of the MPT concept as a simple and effective approach to improve the performance of micronozzle cold gas propulsion devices.

A self‐consistent, non‐equilibrium plasma discharge model is used to describe physical mechanisms and understand different operating regimes of a MHCD. The model includes a surface‐electric‐field dependent secondary electron coefficient description which is essential for the prediction of the different regimes of MHCD operation. At low current (<0.1 mA), the plasma is confined within the cylindrical hollow region of the discharge. At currents above a certain threshold, the discharge expands over the outer flat surface of the cathode. Transient relaxation oscillations (self‐pulsing) of the discharge properties are predicted by the model for intermediate discharge currents ranging from about 0.1 to 0.3 mA.

expands over the outer flat surface of the cathode and operates in the "normal regime". Transient relaxation oscillations are predicted in the plasma properties for intermediate discharge currents ranging from ∼0.1 mA to ∼0.3 mA; a phenomenon that is reported in experiments. The MPT, in its present configuration, is found to operate as an electrothermal, rather than as an electrostatic thruster. A significant increase in specific impulse, compared to the cold gas micronozzle, is obtained from the power deposition into the expanding gas. For a discharge voltage of 750 V, a power input of 650 mW, and an argon mass flow rate of 5 sccm, the specific impulse of the device is vii increased by a factor of ∼1.5 to a value of 74 s. The microdischarge remains mostly confined inside the micronozzle and operates in an abnormal regime. Gas heating, primarily due to ion Joule heating, is found to have a strong influence on the overall discharge behavior. The study provides crucial understanding to aid in the design of direct-current microdischarge based thrusters.

We present a self-consistent 2-D multispecies multitemperature model of dc nonequilibrium surface plasma discharge phenomena in the presence of a low-pressure imposed high-speed convective flow. For pressures of a few torr and voltages of a few kilovolts, a nonequilibrium glow discharge is generated between the electrodes. Peak charge densities in the discharge on the order of 10 14 − 10 16 m −3 , electron temperatures on the order of 1 eV, and gas temperatures on the order of 2000 K are observed. Increasing voltages are found to increase the charge density in the discharge and also cause a constriction of the discharge volume. The same trend is also observed with an increase in the discharge pressure. The discharge is highly asymmetric owing to the high-speed convective flow, with the discharge activity restricted to the flow downstream edge of the cathode surface. The convective flow also causes a quasi-neutral plasma-tail-like feature that provides a major loss mechanism for charged and neutral species in the discharge. Despite sufficient cathode surface area, the discharge operates in an abnormal glow mode, with a positive differential resistivity, owing to a flow-induced constricted cathode attachment. Relatively large cathode sheath dimensions on the order of 1 cm are observed with a net electrostatic forcing restricted to this region. The net electrostatic forcing is largely vertical toward the cathode surface, but also has a component in the direction against the flow.Index Terms-Glow discharge, high-speed flow control, selfconsistent plasma simulation.

Due to their great potential for fuel saving, Contra-Rotating Open Rotors (CRORs) receive renewed interest by the airframers and the engine manufacturers. The inherent high efficiency of this propulsion system, however, is potentially offset by the level of noise emitted by the open blades. The acoustic impact on passengers and community may represent a major issue to their environmental acceptance. Fast and robust noise prediction tools are clearly required to support the development of quieter propellers and their integration in future civil aeronautical transport. The most common strategy for noise estimation consists in a two-step approach, based on the Lighthill analogy: unsteady near-field aerodynamic flow simulation to evaluate the noise sources, coupled to a far-field acoustic propagation code. Focus is given here on two structured grid flow solvers employed to investigate a scale-model of a 12×10 pusher CROR. The unsteady aerodynamic three-dimensional flow is indeed computed for typical cruise conditions using both the nonlinear harmonic method (NLH) of FINE™/Turbo software and elsA’s chorochronic technique. The evaluation of the far-field noise based on the aerodynamic fields is then carried out with the KIM code, Onera’s acoustic propagation code based on the Ffowcs-Williams and Hawkings (FW-H) formulation. The obtained results enable an analysis of the complex aerodynamic interactions between the two propellers that generate interaction tones in the acoustic signature of the propulsion system. A comparison in terms of numerical settings, computational costs and flow fields is performed between the two CFD methods, which show an excellent match of the predicted global performance of the propulsion system. Some differences in the predicted acoustic signatures are discussed in the paper.