小攻角高超声速钝锥边界层中不同扰动对转捩的影响

Effect of Disturbances at Inlet on Hypersonic Boundary Layer Transition on a Blunt Cone at Small Angle of Attack

为了研究上游不同扰动对转捩位置的影响,针对来流Ma=6,攻角1°,半锥角5°的钝锥边界层的转捩进行了数值模拟.首先研究了边界层中小扰动的演化,与流动稳定性理论进行了对比,结果表明:在所考虑的流场中,流动稳定性线性理论可以对扰动的增长率做出一个较好的预测.在此基础上,研究了不同扰动对转捩位置的影响.计算给出了在两种不同频率分布的扰动情况下,转捩位置沿周向的分布.结果表明,转捩位置沿周向分布与入口扰动的幅值和频率有关.某子午面的转捩位置由该处的最不稳定波在入口的幅值决定.根据大多数风洞中背景扰动的特性,解释了小攻角圆锥转捩实验中背风面先转捩,迎风面后转捩的现象.同时,还解释了在背风面附近转捩位置"凹陷"的现象.

To investigate the effect of different disturbances in the upstream,we present numerical simulation of transition for a hypersonic boundary layer on a 5-degree half-angle blunt cone in a freestream with Math number 6 at 1-degree angle of attack.Evolution of small disturbances is simulated to compare with linear stability theory（LST）,indicating that LST can provide a good prediction on the growth rate of the disturbance.The effect of difference disturbances on transition was investigated.Transition onset distributions along the azimuthal direction are obtained with two groups of disturbances of different frequencies.It shows that transition onset is relevant to the frequencies and amplitudes of the disturbances at the inlet, and is decided by the amplitudes of the most unstable wave at the inlet.According to the characters of the environmental disturbances in most wind tunnels,we explain why transition occurs leeside-forward and windside-aft over a circular cone at an angle of attack are explained.Moreover,the indentation phenomenon in transition curve on the leeward is also unpuzzled.