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

Abstract

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 eN 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.