Research On Characteristics Of Backpressure On Two-dimensional Supersonic Inlet

A two-dimensional supersonic inlet was designed to study the effect of geometry parameter of the diffuser on the aerodynamic performance and flow characteristics under inlet design condition,and the characteristics of backpressure and self-excited oscillation of shock train in curved diffuser were investigated through unsteady numerical simulation.First,the influences of the law of the centerline,expansion ratio and offset ratio of diffuser on aerodynamic performance and flow characteristics under inlet design condition were studied.Numerical results indicate that the inlet with diffuser rapid turning in the exit has maximum total pressure recovery coefficient and inlet with diffuser rapid turning in the entrance has minimum total pressure recovery coefficient.As the expansion ratio increases from 1.40 to 1.80,inlet total pressure recovery coefficient,backpressure-resistance ability decrease and the exit Mach number increase.Expansion ratio and offset ratio have both effect on inlet performance.As offset ratio increases,the inlet total pressure recovery coefficient increases at the beginning.But offset ratio increase to more than 0.80,inlet total pressure recovery coefficient decline and the exit Mach number increases.Offset ratio has little effect on the backpressure-resistance ability.Second,the flow characteristics and characteristics of self-excited oscillation of shock train in a typical two dimensional supersonic inlet curved diffuser were studied.The results show that as the back-pressure increased,substantial oscillation and small oscillation interleaved.When the leading shock of shock train intersect with the local background shock,one kind of oscillation that is high frequency and small amplitude is activated,the frequency is above 900 Hz.When the leading point of shock train moves to the place of background shock reflection point at the diffuser up wall,an other kind of oscillation which is low frequency and big amplitude is activated,the frequency is between 200 Hz and 400 Hz.But the oscillation of shock train is a high frequency and small amplitude when shocked locate in the diffuser down wall.The oscillation frequency of shock train and the separation bubble changing frequency are the same.The shape of diffuser and the inverse pressure gradient from background shock are the main causes of big amplitude self-excited oscillation of shock train.Third,the effect of different backpressure change process on flow characteristics and performance of the inlet condition was investigated under normal working.The results show that as the back pressure increases gradually,the total pressure recovery coefficient increase first and then decrease.When the backpressure oscillation,the great the amplitude,the great the total pressure loss.When the frequency is great than 100 Hz,the frequency has little influence on the total pressure loss.Both amplitude and frequency affect the oscillation range of the leading shock of shock train,and the effect is opposite.When the backpressure increases suddenly,the inlet exhibits different flow characteristics at different pressurization rates,but the performance is similar.The translational speed of the leading shock increases with the increase of the pressurization rates.Last,the unstart and restart characteristics of supersonic inlet in the backpressure suddenly change process were investigated.The results show that as backpressure drop from inlet unstart value to normal working value,different depressurization time has a direct impact on restart.The shorter the depressurization time is,the easier the inlet can restart.But the inlet can't restart if the time of depressurization is too long.With the increase of the depressurization value,the maximum depressurization time that inlet can restart Increased.When the time and value of depressurization are big enough,a short period of buzz occurred before the inlet restart.The time and value of depressurization affect the restart characteristics together.