Centerline instabilities on the hypersonic international flight research experimentation HIFiRE-5 elliptic cone model

Linear instability of the three-dimensional boundary-layer over the Hypersonic International Flight Research Experimentation 5 (HIFiRE-5) flight test geometry, i.e. a rounded-tip 2:1 elliptic cone, is analyzed through spatial BiGlobal linear instability analysis, in an effort to understand transition and accurately predict local heat loads on this model of next-generation flight vehicles. The base flow conditions are selected for a Mach 7 flow at altitude of 33.0 km and unit Reynolds number Re ′ = 1.89 × 10 6 m . The base flow is computed using the US3D solver. The three-dimensionality of the boundary-layer on the elliptic cone produces spanwise pressure gradients, inducing crossflow from the leading edge (major-axis meridian) to the centerline (minor-axis meridian) and producing lift-up of low momentum boundary-layer fluid at the centerline. The present analysis focuses on the resulting mushroom-like structure formed near the minor-axis meridian. An unstable fluid structure, which is composed of a low-velocity streak surrounded by a three-dimensional high-shear layer, is thus generated. Results show that this complex fluid structure can sustain linear growth of a number of instability modes, thus confirming earlier analyses which identified such modes without taking surface curvature of the geometry in question into consideration. These so-called centerline modes are associated with varicose or sinuous deformations of the low-velocity streak and are found to have similar growth rates in the frequency range studied, between 50 and 300 kHz. Furthermore, unstable boundary-layer modes, identified as oblique second Mack modes, are unraveled in the vicinity of the centerline. At the conditions studied, Mack modes are found to be less amplified that the centerline modes.