Optimal Design Of Flow Field Of Spacecraft Atmosphere Thermal Cycling Test System

Ground environmental test is a necessary measure to ensure the safety and reliability of spacecraft and to avoid the occurrence of spacecraft accidents.Thermal test can test the correctness of spacecraft thermal design,expose the quality defects of product materials and manufacturing,and is the most important ground environmental test for spacecraft reliability.As a thermal test under atmospheric pressure,thermal cycling test has become a routine test item in spacecraft development process at home and abroad in recent years because of its high temperature change rate,high test efficiency,short test cycle,wider temperature controllable range,lower cost,relatively simple test,and more conducive to the efficient detection of early faults.The thermal insulation performance,humidity level and temperature uniformity of spacecraft atmospheric thermal cycle test system are important performance indicators.Compared with other space powers,the theoretical research on heat transfer and flow mechanism in spacecraft atmospheric thermal cycle test system started late in China,and there is an urgent need for breakthroughs in key technologies such as ultra-low dew point temperature realization and temperature uniformity control in thermal cycle test.Aiming at the application requirement of aerospace engineering for atmospheric thermal cycling test system,this paper focuses on the realization of ultra-low dew point temperature and the control of temperature uniformity in the test space,combines theoretical analysis with numerical calculation,and optimizes the flow field and airflow organization of the system by exploring the mechanism of heat and moisture transfer in the system space,so as to provide an atmospheric thermal cycle test for spacecraft.The test system provides guidance for dehumidification and variable temperature conditions in practical engineering applications.The details are as follows:Firstly,taking the chamber space of the atmospheric thermal cycle test system as the research object,the key performance indexes of the system are determined.According to the test insulation demand,the thermal insulation structure of the chamber is designed by thermal calculation,which is coated with glass fiber cotton,rubber plastic cotton and polyurethane insulation layer.Thereby,the cold and heat loads of the test system under different working conditions are measured and calculated,so as to select the equipment for supplying cold and heat sources of the system.After that,the numerical calculation method verifies that the flow field in the box under the action of reverse buoyancy lift has better temperature uniformity,and analyses the merits and demerits of different air supply and return modes in the test space in terms of temperature change efficiency and temperature field distribution,thus establishing the principle of the design of air distribution mode of the system,i.e.,vertical orifice plate air supply and central air return which ensure the flow field to be subjected to reverse buoyancy force.The work flow of dehumidification,temperature change and heat preservation of the system is considered,which provides a reference for the construction of practical projects.Then,the applicability of the existing dehumidification technology is analyzed,and the dehumidification process of spacecraft atmospheric thermal cycle test system is designed by using cooling dehumidification and adsorption dehumidification technology.An open cycle method for replacing the wet air in the chamber after making dry air from atmosphere is proposed,and a closed cycle method for directly stimulating the gas in the test space to enter the dehumidification equipment and carrying out cyclic dehumidification is proposed.Engineering analysis and numerical calculation are carried out to verify the two methods.After economic check,the closed cycle dehumidification scheme of the dryer is finally chosen.Then,taking the test space of atmospheric thermal cycle test system under dehumidification condition as the research object,the steady-state distribution and dynamic change of humidity field in the chamber were investigated,and the mechanism of the buoyancy lift in the same direction or in the opposite direction and the corresponding reflux structure affecting the humidity field distribution in the chamber was explored.The numerical results show that the humidity field under the action of the same buoyancy lift is stratified in the vertical direction and the displacement efficiency is high,while the humidity field under the action of the reverse buoyancy lift is complex and the displacement efficiency is low.Based on the conclusion of the mechanism of buoyancy on temperature distribution,a certain application requirement is set,and the optimal design of buoyancy parameters is carried out under the conditions of both variable temperature and dehumidification.Finally,taking the test space of spacecraft under normal pressure and thermal cycle as the research object,the temperature field distribution under load condition is studied by numerical calculation method,compared with that under no-load condition.The results show that the heat capacity of the spacecraft and its blocking and viscous effects on the gas inflow interfere with the temperature variation process and the uniformity of the temperature field in the chamber.In order to solve this problem,a compensation scheme is designed to provide the compensating air flow perpendicular to the original gas flow and promote the full heat transfer of the flow field in the test space.The simulation results show that it can offset the influence of the spacecraft on the flow field temperature to a certain extent,and the correction effect is remarkable.