高超声速飞行器尾喷管中磁流体发电机性能数值研究

Numerical Investigation for Performance of MHD Generator in Hypersonic Vehicle Nozzle

关键词:  磁流体动力学  MHD发电机  发电性能  端部效应  电极对

Key words:  Magnetohydrodynamic  MHD generator  Power generation  End effect  Electrode pairs

摘要:

高超声速飞行器因无涡轮而失去发电能力，利用尾喷管中磁流体（Magnetohydrodynamic，MHD）发电机进行发电可以有效解决这一问题。本文采用Fluent商业软件对高超声速飞行器尾喷管中MHD发电机的性能进行了数值研究。研究发现，当磁流体发电通道入口气体的马赫数设置为1.1时，入口气体的马赫数被迫降低至亚声速时，其才能流进通道，但气体的速度沿流向不断上升，并在发电通道出口处达到当地声速。局部磁场使MHD发电机两端出现了端部效应，导致MHD发电机的进出口附近产生了涡电流，进而降低了MHD发电机的性能。在端部效应和MHD射流效应的耦合下，发电通道流向横截面中心的气体总焓沿流向非均匀下降，在发电机入口电极处，其总焓略有增加并达到最大值；在发电机出口电极处，其总焓出现一极小值；横截面上气体总焓的平均值沿流向却均匀下降。不同电极对数的MHD发电机的数值结果表明，分段电极法拉第型MHD发电机的电极对数越多，MHD发电机内的霍尔效应越弱，焓提取率与发电效率越高。当6对电极的MHD发电机分别忽略和考虑霍尔效应时，其焓提取率相差了0.05%，发电效率相差了6.5%。

Abstract:

The power generation capacity of hypersonic vehicle will be lost without turbines， the problem can be effectively solved by utilizing Magnetohydrodynamic （MHD） generator in hypersonic vehicle nozzle. Herein， the performance of the MHD generator in hypersonic vehicle nozzle under the local magnetic field was investigated in this study by Fluent Code. When the inlet gas Mach number of the MHD channel was set to 1.1， the gas Mach number was declined to subsonic， which made the gas flow into the channel， but the velocity of gas increased continuously along the flow direction and could be reached the local speed of sound at the outlet of the MHD channel. The local magnetic field can make the both ends of the MHD generator appear the end effect， which results in eddy currents near the inlet and outlet of the MHD generator， and thus reducing the performance of the MHD generator. Under the function of the end effect coupled with the MHD jet effect， the total enthalpy of the gas was inhomogeneously decreased on the center of flow cross section， its total enthalpy had a little bit increment and reached the maximum value at the inlet electrode of MHD generator and the total enthalpy was dropped to the minimum at the outlet electrode of MHD generator， but the average total enthalpy on the flow cross section was declined homogeneously along the channel. Numerical results of the MHD generators with different electrode pairs show that the more electrode pairs of Faraday type MHD generator are， the weaker the Hall effect is， the higher the enthalpy extraction rate and the power generation efficiency are. When the Hall effect is ignored and considered respectively， the enthalpy extraction rate and the power generation efficiency are different by 0.05% and 6.5% respectively with 6 electrode pairs.