高超声速边界层转捩对高超飞行器热防护及气动布局至关重要。研究依托于JF-12复现高超声速飞行条件激波风洞开展边界层转捩实验，实验模型为典型外形的大尺度平板(长3.2m)和大尺度圆锥(高3m)。大尺度模型结合复现来流条件还原飞行条件下高超声速边界层转捩的物理过程。研究采用数值模拟和实验相结合的方法，针对大尺度平板模型开展关于单位雷诺数、马赫数、气流总温对高超声速平板边界层转捩的研究；针对大尺度圆锥模型开展关于单位雷诺数、马赫数、壁面条带以及攻角对高超声速尖锥边界层转捩的研究；针对钝度影响边界层转捩开展大尺度平板结合不同前缘钝度以及大尺度圆锥结合不同头部钝度的实验研究。利用高精度同轴热电偶传感器和高频响脉动压力传感器分别测量高超声速边界层转捩过程中的壁面热流以及脉动压力。通过热流分布判断边界层转捩位置，对流态进行识别；通过壁面脉动压力分布关注边界层中不稳定波的演化。主要研究内容和创新性成果如下：

1）首次开展了复现飞行条件下大尺度平板边界层转捩实验，获得了来流马赫数、单位雷诺数和总温对平板边界层发展和转捩的影响规律。随着来流马赫数的增加，转捩雷诺数增大，转捩位置推迟，转捩区长度变短，平板边界层层流阶段会快速转捩到湍流阶段。来流马赫数的增加，影响边界层内不稳定波的峰值频率，使得边界层内高频及低频分量转换变慢，边界层失稳变慢，转捩推迟。随着单位雷诺数的增加，转捩空间位置前移，转捩雷诺数增大。单位雷诺数的变化不影响层流边界层内不稳定波特征频率，使得扰动能量在不同频段传递分配。单位雷诺数的增大，扰动演化进程变慢，边界层转捩失稳速率变慢，转捩推迟。总温变化不影响平板层流区热流系数分布，但调制边界层内不稳定波特征频率和重新分配扰动能量。

2）首次开展了复现飞行条件下大尺度尖锥边界层转捩实验，获得了来流参数、壁面条带和攻角对尖锥边界层发展和转捩的影响规律。随着来流马赫数的增加，转捩雷诺数增大，转捩位置推迟，转捩区长度变长。来流马赫数的增加，边界层内不稳定波演化处于更早期阶段，边界层转捩推迟。随着单位雷诺数的增加，转捩空间位置提前，转捩雷诺数减小，圆锥模型对单位雷诺数的变化敏感，转捩空间位置的变化比例远大于单位雷诺数本身的变化比例。单位雷诺数增长使得边界层内不稳定波向扰动演化后期发展，边界层失稳提前。在尖锥前缘布置壁面条带，使得边界层转捩提前。改变尖锥头部的壁面条带激发边界层内高频不稳定波，扰动特征趋于非线性演化阶段，导致转捩提前。10^°攻角条件下，马赫数的增加使得边界层发展趋于不稳定状态。随着单位雷诺数的增大，在圆锥迎风面的转捩雷诺数增大，圆锥侧面转捩雷诺数减小。

3）通过改变平板模型的前缘和圆锥模型的头部钝度，得到了大尺度模型钝度影响边界层转捩规律。平板模型在固定钝度(前缘钝度半径5 mm)出现边界层“转捩反转”现象，这是由单位雷诺数在不同范围的增长对边界层内不同频段不稳定波的影响相反导致的。在平板变钝度实验中随着前缘钝度雷诺数的增长，转捩雷诺数持续增长，整体呈现转捩推迟的现象，增大平板前缘钝度使得边界层扰动趋于早期的演化阶段，边界层转捩位置推迟。对于不同圆锥头部钝度，其转捩雷诺数均随着单位雷诺数的增长呈现减小的趋势；而在同一单位雷诺数条件下，随头部钝度雷诺数增长，转捩雷诺数呈现“转捩反转”的现象，圆锥头部钝度增长对边界层内不同频段不稳定波的调制作用使得转捩雷诺数出现反转的现象。在10^°大攻角条件下，钝度小范围变化时，转捩雷诺数随着钝度雷诺数的增加而增大，边界层转捩推迟。钝度进一步的增长，圆锥迎风面转捩位置不变，靠近背风面的侧区随着钝度增大，转捩空间位置推迟，靠近迎风面的侧区随着钝度增大，转捩空间位置前移。随着模型钝度的增大转捩雷诺数整体呈现先推迟而后稳定的趋势。

Hypersonic boundary layer transition is crucial for the thermal protection and aerodynamic layout of hypersonic vehicles. The research relies on the JF-12 hypersonic shock tunnel duplicating flight conditions to carry out hypersonic boundary layer transition experiments. The experimental models are large-scale flat plates (3.2 m in length) and large-scale cones (3 m in height) with typical simple configurations. In this paper, the truest boundary layer transition evolution process was restored by reproducing the flow field closest to that during real flight and the model closest to the scale of the aircraft. The study used a combination of experiments and numerical simulations. For the large-scale flat plate models, the effects of unit Reynolds number, Mach number, and total temperature on the hypersonic boundary layer transition are studied. For the large-scale cone models, the effects of unit Reynolds number, Mach number, wall strips and angle of attack on the hypersonic boundary layer transition are studied. For the research on the effects of bluntness in hypersonic boundary layer transition, the influences of the flat-plate variable leading-edge model and the cone variable nose-tips model on the boundary layer transition were analyzed. The high-precision coaxial thermocouple sensor and the high-frequency fluctuating pressure sensor were used to measure the wall heat transfer and pressure pulsation during the hypersonic boundary layer transition, respectively. The boundary layer transition position is judged by the wall heat transfer distribution, and the boundary layer flow regime is identified. Focus on the instability waves evolution in the boundary layer through the wall fluctuating pressure distribution. The main research contents and innovative results are summarized as:

1) The large-scale flat-plate boundary layer transition experiments were carried out under duplicating flight conditions for the first time, and the influence laws of Mach number, unit Reynolds number and total temperature on the development and transition of flat-plate boundary layer were obtained. With the increase of the Mach number, the transition Reynolds number increases, the transition position is delayed, the length of the transition zone becomes shorter, and the laminar boundary layer rapidly transforms to the turbulent stage. The Mach number affects the peak frequency of instability waves in the boundary layer. And it makes the conversion of high-frequency and low-frequency components in the flat-plate boundary layer slowdown, which leads to the slowdown of the boundary layer destabilization and the delayed transition. As the unit Reynolds number increases, the transition spatial position moves forward, and the transition Reynolds number increases. The change in the unit Reynolds number does not affect the instability waves characteristic frequency in the laminar boundary layer. And it makes the perturbation energy in the flat laminar boundary layer transfer and distribute in different frequency bands. With the increase of the unit Reynolds number, the disturbance evolution process becomes slower, the boundary layer transition instability rate becomes slower, and the transition is delayed. The total temperature does not affect the heat transfer coefficients distribution in the flat-plate boundary layer laminar stage, but it modulates the eigenfrequency of instability waves and redistributes the disturbance energy in the boundary layer.

2) The large-scale sharp cone boundary layer transition experiments were carried out under duplicating flight conditions for the first time, and the influence laws of incoming flow parameters, wall strips and angle of attack on the development and transition of cone boundary layer were obtained. With the increase of the Mach number, the transition Reynolds number increases, the transition position is delayed, and the length of the transition zone becomes longer. The Mach number makes instability wave in the conical boundary layer develops to the early evolution stage, which leads to the slowdown of the boundary layer destabilization and the delayed transition. With the increase of the unit Reynolds number, the transition spatial position advances, and the transition Reynolds number decreases. The cone model is sensitive to the change in the unit Reynolds number, and the change ration of the transition position is much larger than the change in the unit Reynolds number itself. The increase of the unit Reynolds number makes the instability wave in conical boundary layer develop to the later evolution stage, and the boundary layer is destabilized earlier. For the study of conical boundary layer transition control, analyzed the transition position and instability distribution of the boundary layer under the same flow field for the sharp cone model with different wall strips. The effective boundary layer transition control can be achieved by arranging the wall strips in the laminar boundary layer, so that the transition position can be advanced. Changing the wall strip of the cone nose-tip can excite high-frequency instability waves. Under the action of high-frequency instability waves, the disturbance tends to the nonlinear evolution stage, leading to an early transition. Under the condition of 10^° angle of attack, the increase of Mach number makes the development of boundary layer tend to be unstable. With the increase of the unit Reynolds number, the transition spatial positions all move forward, but the transition Reynolds number increases in the windward region but decreases in the side region.

3) By changing the leading-edge of the plate model and the head bluntness of the conical model, the bluntness influence laws of large-scale model boundary layer transition were obtained. For large-scale flat-plate model, the boundary layer “transition reversal” phenomenon occurs in a single bluntness model. Combined with the analysis of its instability waves, it is found that the increase of the unit Reynolds number in different ranges has opposite effects on the boundary layer instability waves in different frequency bands, which leads to this phenomenon. In the flat-plate bluntness experiment, with the increase of the bluntness Reynolds number, the transition Reynolds number continued to increase, and the overall transition was delayed. Combined with instability wave analysis, it is found that increasing the flat-plate bluntness makes the disturbance tend to the early evolution stage, and the boundary layer transition position is delayed. For different nose-tip models, the transition Reynolds number shows a decreasing trend with the increase of the unit Reynolds number; for the same unit Reynolds number, with the increase of the head bluntness Reynolds number, the transition Reynolds number overall presents “transition reversal” phenomenon. Combined with instability wave analysis, it is found that the different modulation effect on different frequency bands with the increase of cone bluntness makes the transitional Reynolds number reverse phenomenon. Under the condition of 10^° angle of attack, when the head bluntness changes in a small range, the transition Reynolds number increases with the increase of the bluntness Reynolds number, and the boundary layer transition is delayed. With the further increase of the head bluntness, the transition position of the cone windward region remains stable, the transition spatial position of side region close to the leeward region increases is delayed, and transition spatial position of the side region close to the windward region is moved forward. Under the condition of this large angle of attack, with the increase of head bluntness, the overall transition Reynolds number tends to be delayed first and then stabilized.