二维弯曲等截面管道中的激波串特性研究

利用Carroll的试验数据验证了数值方法的有效性之后,对二维等截面弯曲管道中激波串的特性进行了数值模拟试验,研究了管道弯曲对激波串的结构与特征长度、壁面沿程静压分布、出口截面马赫数与总压恢复、反压特性等的影响,研究中考虑了不同的进口马赫数和边界层厚度。结果表明,管道弯曲对流动的对称性有着明显影响,当马赫数较高时(如Ma₀=2.45)合适程度的管道弯曲有利改善直管道已有的流动不对称,使激波串长度缩短。管道弯曲能够有效抑制出口压力变化所导致的出口截面马赫数的大幅波动,考虑到低压比时(出口Ma_e>1)直、弯管道之间总压恢复系数存在明显差距,而当压比较高时(出口Ma_e<1)两者相当接近,因此亚燃发动机的超声速扩压器可适当使用大曲率以缩短管道的轴向长度。另外,鉴于弯曲管道与直管道内激波串长度之间的明显差异,已有的基于直管道的激波串长度经验公式不能很好地适用于弯曲管道。

Characteristics of Shock Train in Two Dimensional Bends with Constant Area

After the validation of CFD method with Carroll’s experimental data, the characteristics of shock train in two dimensional bends with constant area are numerically studied in this paper, on which the influence of coming Mach number and coming boundary layer thickness are also obtained. The investigation is focused on the structure and length of the shock train, the static pressure distribution along the wall, the Mach number and total pressure recovery at the exit section and the back pressure process of the duct with comparison of the straight duct. Results show that a duct with appropriate curvature can improve the symmetry of the flow pattern and shorten the shock train at high coming Mach number (e.g. Ma₀=2.45). The use of the bend can suppress the fluctuation of the Mach number at the exit caused by the change of the back pressure. Because the gap of total pressure recovery of the straight duct and the bend duct is obvious at a low back pressure (Ma_e>1) and noteless at a high back pressure(Ma_e<1), a bend duct with high curvature is recommended for a ramjet to shorten the axial length of the duct. The existing empirical correlation based on straight duct can not predict well the length of shock train in bend duct due to their distinct difference in shock train length.