Transition Mechanisms on Blunt Re-Entry Capsules With and Without Roughness

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Abstract

The boundary-layer state significantly affects the thermal load of objects flying at supersonic or hypersonic speeds. Therefore, the main objective of the work is to quantify the disturbance growth of possible transition mechanisms on blunt spherical re-entry capsules with smooth and rough surfaces at Mach 5.9 wind tunnel conditions using linear instability theory. To this end, a new instability code has been developed based on two-dimensional linear eigenvalue analysis and plane-marching parabolized stability equations (PSE-3D). It is shown that under the given wind tunnel conditions, no modal disturbance growth occurs on the capsule with a smooth surface, and the non-modal growth is insufficient to trigger transition. In the second part of the work, the impact of a generic discrete roughness element on the flow field and the growth of instabilities developing in its wake is systematically quantified for various roughness parameters. Furthermore, the impact of the local pressure gradient on the wake-mode instability characteristics is scrutinized for the first time. The last part of the work addresses the potential of optimal non-modally growing disturbances in the wake of a micron-sized distributed roughness patch to trigger transition. For this study, the variational approach of direct and adjoint PSE-3D is used for the first time.

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• Transition Mechanisms on Blunt Re-Entry Capsules With and Without Roughness. (deposited 03 Nov 2021 13:57) [Currently Displayed]