| Hypersonic vehicle is next generational aircraft/spacecraft designed for the surveillance missions,military strikes and space transportation.The electric demand of hypersonic vehicles is extremely huge,which is mainly caused by the fuel-supply,radar system,flight control and laser weapon,but the existing onboard power devices can be hardly applied.In order to satisfy the demand on the electric supply for hypersonic vehicles with finite cold source,a combined power generation system scheme based on cold source cascade utilization,was put forward.To evaluate the performance of combined power generation system and predict the power generation capability under typical flight conditions,the following reseaches were carried out.To solve the problems of open cycles,a closed power generation system was proposed for onboard high-power thermoelectric conversion.Closed power generation system may be a more reasonable choice for accelerated hypersonic vehicles,since it exhibits better than open cycles in overall flight envelope.Compared with ground-based closed thermodynamic cycles,the cold source of onboard closed power generation system has few kinds,general heat sink and small quantity,making it extremely finite.Besides,the power of closed cycle system with finite cold source is determined by the mass flowrate and available enthalpy difference of fuel,as well as thermal efficiency of cycle.Performacne analysis of closed-Brayton-cycle(CBC)under the finite cold source condition was performed,and the effect of cold source types was analyzed.Results indicate that cryogenic fuel is a better choice as the old source of CBC,and power optimization becomes more necessary when normal-temperature hydrocarbon fuel is applied as cold source.There is an optimal cold source temperature difference for power,under the influence of the cooling capacity of fuel and the thermal efficiency of system.For supercritical carbon dioxide CBC with finite cold source,simple recuperated layout exhibits better on the system structure and power output than recompressing layout.However,the cooling capacity of fuel is not utilized fully by CBC.A new modeling method for multi-stage thermoelectric generator(TEG)which is regarded as a performance enhancement approach of CBC,was developed with the temperature variation of cold and heat source along the flow direction.The influencing factors on thermoelectric performance was analyzed and the optimization on stage numbers was performed.It shows that the geometry factor and inlet temperature of heating channel have significant effects on the TEG performance.Compared with single-stage TEG,the improvement of power density and conversion efficiency are as high as 79.1% and 96.5% respectively.Considering the issues of manufacture,the optimal stage numbers are three and four.At last,a heat supply system model for power generation based on quasi-onedimentional scramjet combustor cooled by liquid metal was established,and performance comparison with a heat supply system on the basis of regenerative cooling.Results indicate that the former achieves better heat supply capacity than the latter on the premise of well-designed thermal protection.A novel combined power generation system of closed-Brayton-cycle and thermoelectric generator(CBC-TEG)was proposed based on the cascade utilization of cold source,and its performance was evaluated.Results show that the power of closed power generation system is enhanced successfully by means of TEG,and the highest increase percent reaches 53.6% against CBC without the limit of heating process.Besides,when coupled with a hydrocarbon fueled scramjet,the combined power generation system achieves a power improvement of 33.4%.This research provided a new technical solution for the high-power electricity supply of hypersonic vehicles,and a foundation for the detailed design and engineering application in the future. |
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