Boundary-Layer Transition-Onset Variation Under Wide Range of Mach Numbers and Wall Temperature Ratios

Abstract

Linear stability analysis is carried out for the boundary layer under a wide range of Mach numbers ([Formula: see text]) and wall temperature ratios ([Formula: see text]), and for the first time, the characteristics of the third mode are analyzed under different [Formula: see text] and [Formula: see text]. It is found that the unstable third mode appears at [Formula: see text] with an adiabatic wall, and its growth rate first increases and then decreases with increasing [Formula: see text]. As the wall becomes colder, the unstable third mode is enhanced and appears at lower [Formula: see text]. The transition-onset variations are investigated by the [Formula: see text] method. As [Formula: see text] reaches 14, the third mode begins to promote the transition. The transition-onset Reynolds number of the third mode can be reduced by 11.4% compared to that of the second mode at [Formula: see text]. The transition-onset momentum thickness Reynolds number [Formula: see text] varies significantly under different [Formula: see text] and [Formula: see text]. At [Formula: see text], [Formula: see text] is around 800–2000 and increases with increasing [Formula: see text] significantly. At [Formula: see text], [Formula: see text] rises to 2000–3800 and is less sensitive to the change of [Formula: see text]. Therefore, it is necessary to consider the effects of [Formula: see text] and [Formula: see text] on [Formula: see text] in transition prediction modeling for hypersonic boundary layers.