In order to achieve the rapid catalytic ignition startup of Hydroxylammonium Nitrate (HAN)-based monopropellant thrusters under low-temperature conditions (below 0 ℃), a gas dynamic resonance internal heating method is adopted to centrally heat the front section of the thruster’s catalyst bed. Three low-temperature (-9 ℃) startup tests are conducted on a 20 N HAN-based monopropellant thruster, and the heat transfer process inside the combustion chamber of the internally heated monopropellant thruster is studied through system simulation calculations. The test results show that using nitrogen as the resonant working medium, the HAN-based thruster can achieve rapid catalytic ignition and startup under low-temperature conditions, reducing the preheating time required for traditional catalyst bed electric heating from tens of minutes to tens of seconds, and significantly shortening the ignition delay time; the preheating time for low-temperature pre-pulse ignition is reduced to approximately 20 s. The heat transfer calculation results show that the resonance heater can stably output a heating power of about 30-35 W; during the pre-pulse ignition phase, the pressure rise gradient is large, and the thermal accumulation effect promotes the rapid temperature rise inside the combustion chamber. At the end of this phase, the temperature difference between the casing and the catalyst bed is about 500 ℃; in the pulse operation phase, the catalyst bed is already at a relatively high temperature level, and the temperature difference between the casing and the catalyst bed is about 200 ℃; during the continuous operation phase, due to the continuous supply of propellant, the maximum temperature inside the catalyst bed can reach about 1 150 ℃, with a temperature difference of about 600 ℃ from the casing. The application of gas dynamic resonance heating method can realize the rapid catalytic ignition startup of HAN-based monopropellant thrusters under low-temperature conditions.

The influence of unsteady pulsating high pressure in the air-breathing rotating detonation engine combustor on the flow characteristics of inlet is analyzed to guide the design of the inlet. The temporal-spatial characteristics of the pressure in the outlet section of inlet were considered, and the propagation processand flow characteristics of the moving shock wave in the inlet were simulated by adopting the three-dimensional unsteady numerical simulation method. The shape characteristics, propagation velocity, pressureand other key parameters of the moving shock wave were analyzed, and the flow lossand the influence of the angular frequency, peakand time-average values of the pulsating back pressure on the flow characteristics were obtained. It was found that the moving shock wave led to the flow characteristics of low-pressure airflow pressurizationand decelerationand high-pressure airflow decompressionand acceleration in the inlet. Compared with the steady back pressure condition, the influence boundary of pulsating back pressure was more upstream. The higher the angular frequency, the longer the circumferential length, the narrower the width of the oscillation region, the more times the flow passed through the shock wave; however, the average total pressure loss of the outlet at different angular frequencies basically remained unchanged. When the angular frequencyand the time average pressure ratio were respectively kept constant at 12 000 rad/sand 19.1and the pressure peak value ranged from 0.5 to 1 Mpa, the average total pressure loss of the outlet varied from 43% to 46%. When the angular frequencyand peak pressure ratio were respectively kept constant at 12 000 rad/sand 49.5and the time-average pressure increased from 0.22 to 0.32 MPa, the average total pressure loss of the outlet decreased from 52% to 40%. Compared with the steady back pressure condition, the total pressure loss was 2% to 8% larger. The results show that the unsteady pulsating back pressure leads to the big differences between the flow characteristics of the air-breathing rotating detonation engine inletand the traditional engine inlet. In the inlet of air-breathing rotating detonation engine, the flow loss is larger, and the influence boundary of shock wave is closer to the upstream.

Hydraulic dynamics analysis of the pressurized supply system is needed in the process of longitudinal structure stability analysis of the launch vehicle. The method of calculating the accumulator’s resistance directly affects the accuracy of the dynamic analysis of the supply system. At present, the commonly used method is to ignore the influence of the fluid flow inside the propellant supply system and to analyze the accumulator resistance with an orifice flow model. However, this method has large errors. In this paper, by introducing the communication port flow model, the non-linear resistance calculation formula of the accumulator is deduced, where the influence of the vertical flow in the propellant supply system is considered. Then, this theoretical calculation method is verified by conducting a steady-state simulation on an accumulator. Under the various situations, it is discovered that the nonlinear resistance calculation approach suggested in this study may greatly increase prediction accuracy within a variation of less than 10%, whereas predictions based on the orifice flow model have deviations above 30%. The linear resistance theoretical formula under quasi-steady condition is further deduced and the linear resistance curve is drawn. The linear resistance of the accumulator was found to have a minimum value, which is related to the total flow area of the communication port and the velocity of propellant inside the main pipe.

The solid rocket motor grain reverse design, an effort to seek the optimal grain shape to match a given internal ballistic curve, can be used to guide the conceptual design of brand-new grains. Grain reverse design is now progressing from the size optimization level towards the shape optimization and even topology optimization level. Shape optimization problems tend to have large degrees of freedom and high nonlinearity, placing extremely high demands on the computational efficiency of burn-back analysis. However, existing elliptic algorithms for burn-back analysis fail to meet the requirement. It is necessary to develop an efficient elliptic algorithm for burn-back analysis and apply it to the 3-dimensional (3D) grain reverse design. Firstly, the eikonal equation is linearized to a Helmholtz equation and a Poisson equation, forming a series of Fast Heat Conduction (FHC) methods for burn-back analysis. Among them, the f-FHC method, describing the grain geometry by cavity fraction distribution, uses the LDL decomposition method to solve the linear equations. With the principle of “once decomposition, back substitution everywhere”, the computational efficiency can be significantly improved. Secondly, the key issues of 3D grain reverse design are systematically analyzed, including the selection of objective function, the range of independent variables that need to be optimized, isolated holes identification, and casting requirements. With the aid of the evolutionary neural network, the Grain Reverse and Intelligent Design (GRID) system is developed. The calculation results show that the f-FHC method can reduce the calculation time of 3D grain burn-back analysis into less than 1 s. Targeting at the burning surface curve or internal ballistic curve of the dual-thrust grain, the GRID system successfully designs a series of new grains containing complex 3D internal cavities. The resulting grains meet the casting requirements, and their mandrels can be manufactured by 3D-print. The proposed algorithm and the developed software can provide support for the conceptual design of brand-new grains.