| In order to discover the influence of the skin-juncture on the transition position, and more accurate predict transition position using eN method for flat boundary-layer with concave groove. Direct numerical simulation and stability analysis method are carried out to investigate the disturbances evolution in hypersonic boundary layer. Three roughs are discussed, in the situation as following: Reynolds' number are 30000 and 50000; Mach is 4.5; isothermal wall; the sizes of rough are l×h=0.1?0×0.05?0?0.5?0×0.25?0?1?0×0.5?0.1?the effect of rough on the basic flow is just near the rough and the location of the rough. There is backflow in rough, and velocity of flow is related to the size of rough. The much bigger size holds the faster velocity. The maximum velocity of backflow appears in the center location, when the size of rough is e l×h=0.1?0×0.05?0. But the maximum velocity of backflow does not appear in the center location for the others. It is near the right border of rough. And the location of the maximum velocity is much closer to the right border of rough with the growing size of rough.2?The effect of concave groove on the evolution of disturbance is related to the size of rough. When the size of rough is l×h=0.1?0×0.05?0, it only causes fluctuations in rough. The evolution of disturbance becomes same after rough. The other two have suppressed effect on the evolution of disturbance in some extent, but after rough the influence of growth rate is little. Growth rate tend to be stable and is same as the growth rate of flat after a period of fluctuation.3?e N method could be used to predicted the position of transition. When the size of rough is small, the effect of rough could be ignored. And the smooth flat can take place of the flat with a concave groove. When the size of rough is bigger, the position of transition can be predicted more accurate by e N method combined with stability analysis, and a correction factor of N. |
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