DSMC Simulation of the Effect of Needle Valve Opening Ratio on the Rarefied Gas Flows inside a Micronozzle with a Large Length-to-Diameter Ratio

Abstract

The cold gas micro-propulsion system can provide low noise and ultra-high accuracy thrust for satellite platforms for space gravitational wave detection, high-precision earth gravity field measurement. In this study, the effect of different needle valve opening ratios on the rarefied flow characteristics of a micro-nozzle in a cold gas micro-propulsion system was investigated based on DSMC method. The special feature of the currently studied micro-nozzle is that it has a section of micro-channel with a large length–diameter ratio up to 4.5. Due to the extremely small needle valve displacement of the nozzle (minimum needle valve displacement up to 1.7 μm), a finely structured mesh was used. The molecular particle and macro flow characteristics inside the micro-nozzle were calculated for the conditions of a needle valve opening ratio from 5% to 98%. The throttling effect of the throat has a significant effect on the rarefied flow in the micro-nozzle; especially under the tiny opening, this effect is more significant. The spatial distribution of continuous flow, transition flow, and free molecular flow in the micro-nozzle varies at different needle valve opening ratios. As the needle valve opening ratio increases, the continuous flow will gradually fill the microfluidic region.

Direct Simulation Monte Carlo Simulation of the Effect of Needle Valve Structures on the Rarefied Flow of Cold Gas Thrusters

“…dsmcFoam is a DSMC solver for rarefied gas dynamics, implemented within the OpenFOAM software framework, and parallelised with MPI [ 40 ]. The nitrogen molecule is considered in the simulation [ 41 ]. The N 2 was treated as polyatomic gas.…”

“…Therefore, the molecular number density and average particle number per cell are set to 5.5 × 10 8 and 65, respectively. A fixed calculation time step is used, which takes the value of 1 × 10 −9 s. The flow state in the micro nozzle reaches a quasi-stable state at 0.1 ms [ 41 ].…”

“…To validate the accuracy of the simulation, thrust data at different flow rates (adjusted through controlling the needle valve opening) were calculated and compared with experimental data obtained under identical boundary conditions. The test setup and test methods are described in reference [ 41 ]. The experiment was conducted with an inlet pressure of 0.15 MPa, working medium temperature of 293.15 K, wall temperature of 293.15 K, and vacuum outlet.…”

“…Therefore, the molecular number density and average particle number per cell are set to 5.5 × 10 8 and 65, respectively. A fixed calculation time step is used, which takes the value of 1 × 10 −9 s. The flow state in the micro nozzle reaches a quasi-stable state at 0.1 ms [41]. Figure 2 illustrates the computational domain of the micro-nozzle, which can be divided into four sections: the inlet section, throat section, microfluidic section, and expansion section [42].…”