基于变均布霍尔系数的磁控热防护系统霍尔效应影响

Investigation of Hall effect on the performance of magnetohydrodynamic heat shield system based on variable uniform Hall parameter model

为研究霍尔效应对磁控热防护系统的影响机理,建立并验证了热化学非平衡流场、外加磁场、感应电场的多场耦合数值求解方法.基于均布霍尔系数模型分析了霍尔效应在两种不同磁场强度B_0、不同壁面导电条件下对磁控效果的影响.研究表明,不同壁面导电性下霍尔效应的影响规律不同.绝缘壁面条件下,考虑霍尔效应后壁面热流的变化是附面层内洛伦兹力的变化与激波层厚度的减小二者共同作用的结果.B_0=0.2 T时洛伦兹力增加附加的流体减速作用占主导,磁控热防护效果优于忽略霍尔效应的情况,并且在霍尔系数为5.0达到最优;而当B_0=0.5 T时,激波层变薄对附面层外缘温度的增加占主导,磁控热防护效果变差,并且随霍尔系数的增加壁面热流越来越大.导电壁面条件下,随着霍尔系数的增加,磁控激波以及热防护效果变差,且当β≥5.0时,磁控热防护系统几乎完全失效.

There has been a resurgence in the field of magnetohydrodynamic （MHD） flow control in the past 20 years. An increasing demand for sustained hypersonic flight and rapid access to space, along with numerous mechanical and material advances in flight-weight MHD technologies, has aroused renewed interest in this subject area. As a novel application of MHD flow control in the thermal protection field, MHD heat shield system has been proved to be of great intrinsic value by lots of researchers in recent years. Although its theoretical feasibility has been validated, there are many problems that remain to be further investigated. Among those problems, the Hall effect is a remarkable one that may affect the effectiveness of MHD flow control. Considering the fact that it is not sufficient to evaluate the Hall effect by merely using the chemical reaction model implemented in the nonequilibrium flow simulation to calculate the Hall parameter, a parametric study is conducted under the assumption of simplified uniform Hall parameter. First, coupling numerical methods are constructed and validated to solve the thermochemical nonequilibrium flow field and the electro-magnetic field. Second, a series of numerical simulations of the MHD head shield system is conducted with different magnitudes of Hall parameter under two magnetic induction intensities （B0 = 0.2 T, 0.5 T）. Finally, the influence of Hall effect on the performance of MHD heat shield system is analyzed. Results indicate that Hall effect is closely related to the wall conductivity. If the vehicle surface is regarded as an insulating wall, the heat flux variation is co-determined by varying the Lorentz forces within the boundary layer and the shock-control effect. Compared with the one neglecting the Hall effect, the heat flux with Hall effect is slightly mitigated as the increase of Lorentz forces in the boundary layer dominates when the stagnation magnetic induction intensity B0 equals 0.2 T. However, the heat flux is increased when B0 equals 0.5 T, because the decrease of shock stand-off distance dominates which increases the gas temperature outside the boundary layer. Moreover, in this case the larger the Hall parameter, the higher the heat flux will be. As for the conductive wall, the performance of MHD heat shield system becomes worse with the increase of Hall parameter, and while it is equal to or higher than 5.0, this system loses its effectiveness.