MF-1钝锥边界层稳定性及转捩天地相关性研究

Investigation on correlation between wind tunnel and flight for boundary layer stability and transition of MF-1 blunt cone

影响高超声速边界层转捩的因素众多,而地面风洞实验无法充分模拟这些因素,使得风洞实验的转捩数据与真实飞行数据通常存在很大差距.为了把地面风洞实验的转捩数据换算到真实飞行状态下,提高转捩预测精度,选用零度攻角7°半锥角的钝锥模型,利用中国空气动力研究与发展中心的MF-1飞行实验、Φ1m高超声速风洞实验数据以及国外飞行实验和风洞实验数据,通过LST和eN方法,对天地工况的稳定性与转捩进行了对比分析.结果表明,天地之间的稳定性与转捩存在较大差异,天上飞行的壁温比小于地面风洞,导致其第二模态频率大于地面风洞.给出了第二模态最不稳定频率的经验关系式,该关系式同时适用于真实飞行工况和风洞实验工况.研究还发现转捩时的N值(N_T)受钝度雷诺数影响很大,钝度雷诺数越大,N_T越小,甚至当钝度很大时,在边界层模态失稳之前转捩就已经发生.钝锥前缘弓形激波后的流场存在熵层,钝度会影响熵层进入边界层的位置(熵吞点).研究表明,转捩点/熵吞点的相对位置与N_T体现出较好的相关性,且天地趋势一致.通过最小二乘法,给出了转捩点/熵吞点相对位置与N_T的经验关系式,该关系式可方便高效地对类似条件下的高超声速边界层转捩进行预测.

Hypersonic boundary-layer transition(BLT)is affected by multifarious factors,some of which cannot be simulated in ground wind tunnels,which makes the BLT data of wind tunnel experiments are usually different to that of flight experiments.In order to convert BLT data from wind tunnels to real flight cases,and to improve BLT prediction accuracy,a blunt cone model with zero angle-of-attack and 7°semi-cone angle is selected to contrastive analysis the boundary-layer stability and transition between wind tunnels and flights by using linear stability theory and e N method,based on the data set of our MF-1 flight test and hypersonic wind tunnel experiments,as well as an abroad flight test and wind tunnel experiments.The results show that the difference of stability and transition between wind tunnels and flights is essential.The wall temperature ratio in flights is smaller than that in wind tunnels,which leads to the second mode frequency in flight tests are greater than that of wind tunnel experiments.Two empirical formulas are developed to compute the most unstable frequency of the second mode.These formulas are shown suitable for both flight conditions and wind tunnel conditions.It is also shown that the N value(N_T)at the start of BLT is greatly affected by the nose Reynolds number.The larger the nose Reynolds number,the smaller the N_T value.When the nose-tip bluntness is large enough,the BLT occurs even without boundary-layer mode instability.The front bow shock waves of blunt bodies will induce entropy layers,and the bluntness will affect the location(swallow point)where the entropy layers merge into the boundary layers.The relative location of transition point and swallow point is shown in good correlation with the N_T,and the trend is similar for both wind tunnels and flights.A correlation between the transition-swallow relative location and the N_T is developed by the least square method.This correlation is expected to conveniently predict hypersonic BLT of similar conditions.