长寿命、高能量密度和高效率的动力系统是实现未来太空探索目标的必要条件，空间反应堆耦合Brayton系统是兆瓦级空间动力系统的最佳选择之一。功率控制特性是满足系统安全高效运行的关键。该文建立了空间堆Brayton系统动态模型，研究了旁路阀控制下系统的升、降功率特性。结果发现：当载荷变化时，旁路阀控制可快速改变系统局部流量；叶轮机械工况、涡轮和压气机功率及系统电功率能快速响应空间设备的用电需求和负载变化作出相应改变；同时，系统载荷变化导致转动部件对轴的扭矩失衡，容易出现超速事故，旁路控制降低涡轮的输出功率，可有效避免转轴超速的风险。在此基础上，研究了旁路阀开度的敏感性影响，结果发现：系统低压侧和辐射散热回路对旁路阀控制引起的参数扰动最为敏感。旁路阀开度增加后，压气机出口高压气体与涡轮出口低压气体混合，使低压侧管道和部件压力升高；辐射器散热功率增加导致散热回路温度升高，因而辐射器需要更大的散热能力。本研究为空间堆Brayton系统的安全稳定运行提供了参考。
[Objective] Long lifespan, compact, high-energy density, and efficient power systems are necessary to achieve future space exploration goals. The space reactor coupled Brayton cycle is high in energy conversion efficiency, small in volume, light in weight, and stable in operation, which is optimal for megawatt space power systems. The power control features are the key to the safe and efficient operation of a Brayton space nuclear power system. The reactor reactivity, inventory, and bypass valve are effective means of system power control. The bypass valve can change the local mass flow rate of a Brayton system and is expected to rapidly control system power to meet the frequently changing load of a space vehicle.[Methods] In this paper, a model of a Brayton space reactor system is established. A system power control simulation program is compiled based on the idea of modular modeling, each component of the system is solved independently, and the mass, momentum, and energy are transferred through data transmission between components. The calculation results of the model in this paper are compared with the simulation results of the startup process in the references, and the accuracy of the program and model is verified. The power-on and power-off transient performance of the system under the control of the bypass valve is investigated, and the effects of the bypass valve opening on system performance are studied.[Results] The power-on and power-off transient results of the system under bypass valve control indicated that bypass valve control could quickly change the pressure and distribution of mass flow rates in the system, the working conditions of the turbine and compressor, and the output power of the system, which could quickly respond to the power demand and load changes of a space vehicle. The change in the load led to a torque unbalance of the shaft, which could further induce rotating shaft overspeed accidents. The strong centrifugal force may damage the blades of the turbine and compressor. The bypass control adjusted the mass flow rate, pressure ratio, and output power of the turbine and compressor, controlled the shaft speed to operate near the rated value and simultaneously avoided the overspeed risk of the rotating shaft. Furthermore, the effect results of the bypass valve opening on system performance showed that the low-pressure side of the system and the radiant heat reject loop were sensitive to the parameter disturbance caused by the bypass valve control. The high-pressure gas at the compressor outlet mixed with the low-pressure gas at the turbine outlet through the bypass valve, and the pressure of the low-pressure side pipes and components increased. The elevated heat rejection power of the radiator increased the temperature of the heat reject loop, and the radiator needed greater heat rejection capacity.[Conclusions] Therefore, bypass valve control is an effective means to control the power and prevent shaft overspeed in a Brayton space nuclear power system. This study provides a reference for operating a Brayton space reactor system.
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