The Evolution Of A Spanwise Wave Packet Disturbance In The Supersonic Flat-plate Boundary Layer

On the research of the evolution of disturbance on three-dimensional supersonicboundary layer, it was found three-dimensional small scale structure downstream. Inorder to study the causes of three-dimensional disturbances, this paper studied theevolution of flat-plate boundary layer with a spanwise wave packet disturbance byusing numerical simulation, which could determine whether is the threedimensionality of the fluid field or the three dimensionality of the disturbance itself tocause the appearance of the three-dimensional small scale structure. It has practicalsignificance that a wave packet disturbance is similar with the wave induced naturally.In this paper, the evolution of two-dimensional and three-dimensional smalldisturbance and a wave packet disturbance on supersonic flat-plate boundary layerwas simulated by using direct numerical simulation (DNS) method. The evolution ofboundary layer with the two-dimensional and three-dimensional small disturbancewas compared with the amplitude curve calculated by linear stability theory (LST),which verified the correctness about the process and would take preparation forcalculating wave packet disturbance. The solutions by using direct numericalsimulation inferred the following conclusions:1、 The solution showed that it arise the three-dimensional stripe structuredownstream which width is much smaller than the one of the wave packeton studying a flat-plate boundary layer with a wave packet disturbance. Itwas also found that this stripe structure correspond to spanwise highfrequency harmonics wave by using Fourier analysis and this wave couldbe increased rapidly to become the main factors of the disturbances.Itwas also showed that the different width of wave packet on the entrancecould cause slightly difference of the scale about the stripe structure.2、 It was deducted that the cause of the appearance of the small scale stripestructure was the three dimensional high frequency components of thedisturbance. The three dimensionality of the boundary layer wouldgenerate three-dimensional small scale stripe structure by inducing three...