高超声速进气道隔离段反压的前传模式及最大工作反压

Back pressure propagation mode and maximum working back pressure of hypersonic inlet isolator

对均匀来流和有斜波入射(非均匀)情况下隔离段内流动进行了数值分析,发现反压增加首先在隔离段出口形成激波串,出口压力不断增加,而隔离段内流动没有变化;进一步增加反压,直到隔离段出口附面层开始分离时,激波串开始往隔离段内移动,壁面压力自激波串第一道激波位置开始逐渐增加;反压继续增加,激波串在隔离段内不断地向前移动。分析了隔离段内激波串的流动特征,发现激波串是由系列“斜激波+附面层分离+加速降压”流动组合而成,激波串后的流动为掺混流动(掺混区)。提出了最大工作反压的概念,当反压等于最大工作反压时,激波串位于隔离段出口,波后附面层开始分离,反压的任何增加,激波串就会往隔离段内移动;当反压小于或等于最大工作反压时,隔离段出口为超声速流动。研究还发现最大工作反压比由零反压时隔离段出口平均马赫数唯一确定,马赫数越大,最大工作反压比越大。最大工作反压比数值可用D.E.Nestler的拟合式来计算。

The flow filed in the isolator of a typical hypersonic inlet was simulated with uniform and non-uniform（with oblique shock） inflow. It was observed that shock trains formed firstly at the exit plane of the isolator with the increase of back pressure, and the flow field in the isolator remained unchanged. The shock trains did not move inward the isolator until the boundary layer began to separate at the exit plane of the isolator when back pressure increased and the pressure on the wan surface began to increase gradually behind the shock train＇s first shock. The shock trains moved forward continually with further increase of back pressure. The shock trains is characterized by ＂oblique shocks ＋ boundary layer separation ＋ flow acceleration and pressure decrease＂. There is a mixing flow （mixing region） behind the shock trains. The concept of Maximum Working Back Pressure was presented. When the back pressure equals to the Maximum Working Back Pressure, the shock trains lies at the exit plane of the isolator and the boundary layer behind the shock begins to separate and any increase of the back pressure will cause the shock trains move inward. When the back pressure is less or equal to the Maximum Working Back Pressure, the flow at the exit of the isolator is in supersonic mode. The Maximum Working Back Pressure Ratio is determined only by the mean Mach mumber at the exit plane of the isolator without back pressure and the greater the Math mumber, the higher the Maximum Working Back Pressure Ratio. The Maximum Working Back Pressure Ratio can be calculated by the D. E. Nestler＇s correlation.