A Study Of Plume Flow And Its Contamination Of The Space Thrusters

The investigation into the plume flow and its contamination of the space thrusters is of great significance both in theory and practice. The domestic research on the plume flow has lagged far behind the excellent laboratory in the word, especially the plume test in high altitude, the plume contamination study, the control and cleanup of the plume contamination, etc. With the development of the space exploration, the investigation into the plume flow and its contamination is becoming a field we cannot avoid.Based on the previous studies, some groping work is carried out on several plume questions, such as the numerical simulation of the space thruster's plume flow, the simulation and test of the space thruster's plume flow on ground, the transport and adsorption analysis of the contaminant on the satellite surface and the performance degradation calculation of the key function surfaces in the satellite (optical system, solar array, thermal control surfaces, and so on) caused by the plume contaminant.The space plume flow research involves some different theories, such as the continuum gas flow, the transition gas flow, the rarefied gas flow and the freedom molecule flow. A single physical model and mathematical method can not solve this problem accurately. So the computational fluid dynamics (CFD) method and the direct simulation Monte Carlo (DSMC) method are combined to simulate the space plume flow. The former is used to calculate the continuum flow in the thruster and the latter is performed in the rarefied gas flow calculation. The combination of the two calculation methods fully exerts the advantage of the two methods and improves the speed and accuracy of the calculation. The single thruster's plume flowfield is calculated and proved by test data, and then the three-dimensional plume flowfield of the four-parallel thrusters is calculated. The plume flowfield comparison is made between the four-parallel thrusters and the single thruster with the same thrust.The experiment of the plume flow is successfully performed in the simulated space environment. A test system is developed, which mainly includes a simulated space environment vacuum facility, an electric-heat-gas simulated thruster, a steady pressure gas supply system, an axial movement device, a radial movement device, a test system and a temperature control system. The test system can correctly simulate and measure the plume flowfield parameter as the thruster firing in the orbit of 100 kilometers. The test data agree well with the numerical results and are compatible with the Boyd's test results under a similar test condition. Thus, that the project of the experiment is proved reasonable and the test accurate.The main parameters of the simulated thruster and the steady pressure gas supply system all meet the design acquirements. The temperature rise range of the gas in the coil tube of the electric-heat-gas simulated thruster is larger than 600 K. The temperature when the gas enters the thruster's combustion chamber closes to the real combustion gas. The variation scope of the gas's total temperature tested in the thruster is less than 0.1%, and the value is about 0.15% of the total pressure. The pitot technique is successfully used in the rarefied ultrasonic plume flow, and the test results are accurate and stable. The measure deviation of the total pressure in the near plume and the far plume is±4Pa and±0.4Pa respectively. The temperature control precision is±1.0K. The temperature and the pressure sensors respond promptly. The reaction time is less than 4.0s when the test results reach 99 percent of the object's real value.The contaminant thickness of the surface depends on the quantity of the arrived contamination molecules, the molecules'adsorption coefficient and the adsorption time on the surface. The quantity of the molecules arrived on the surface is obtained by the plume flow simulation and the contamination molecule transport calculation. The adsorption coefficient is achieved generally from the test data, and it depends on the property of the gas and solid surface. The test data are very limited at present, only highly simplified engineering calculation models are adopted in many cases. The adsorption coefficient in common calculating model is the function of the temperature of the contaminant and the surface. The concept of the effective adsorption time is proposed. In this way, some contamination calculations short of data may be made.The transport of the contamination molecules between the surfaces is one of the most important points in the satellite contamination research. The contaminant transport in the calculation model between the surfaces is divided into visual and non-visual transport. The molecule transport between the visual surfaces is assumed as the free flow without collision. It is similar to the radiation heat-transfer. The non-visual transport includes two parts. One is the backflow coming from the collision between the contaminants, called self-scatter backflow. The other is the backflow coming from the collision between the contamination and environment molecules, called environment-scatter backflow.The effect of the plume contamination on important function surfaces is analyzed, and the contamination calculation model of the molecule adsorption film is developed. Taking the solar array as an example, the power loss calculation caused by the plume contamination is performed. The contamination film weakens the cell's light transmittance, leading to the output power decrease. Meanwhile, the adsorption of the contamination film to the sunlight raise the cell's operating temperature, which makes the cell's electrical conversion efficiency decrease. The total solar array power loss is calculated considering the two effects in combination.