Numerical investigation of roughness effects on transition on spherical capsules

Stefan Hein, Alexander Theiss, Antonio Di Giovanni, Christian Stemmer, Thomas Schilden, Wolfgang Schröder, Pedro Paredes, Meelan M. Choudhari, Fei Li, Eli Reshotko

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

To address the hitherto unknown mechanism of boundary-layer transition on blunt reentry capsules, the role of roughness-induced disturbance growth on a spherical-section forebody is assessed via optimal transient growth theory and direct numerical simulations (DNS). Optimal transient-growth studies have been performed for the blunt capsule experiments at Mach 5.9 in the Hypersonic Ludwieg tube at the Technische Universität Braunschweig (HLB), which included measurements behind a patch of controlled, distributed micron-sized surface roughness. Transient-growth results for the HLB capsule indicate similar trends as the corresponding numerical data for a Mach 6 experiment in the Actively Controlled Expansion (ACE) facility of the Texas A&M University (TAMU) at a lower Reynolds number. Both configurations indicate a similar dependence on surface temperature ratio and, more important, rather low values of maximum energy gain. DNS are performed for the conditions of the HLB experiment to understand the generation of stationary disturbances by the roughness patch and the accompanying evolution of unsteady perturbations. However, no evidence of either modal or nonmodal disturbance growth in the wake of the roughness patch is found in the DNS data; thus, the physical mechanism underlying the observed onset of transition still remains unknown.

Original languageEnglish
Pages (from-to)388-404
Number of pages17
JournalJournal of Spacecraft and Rockets
Volume56
Issue number2
DOIs
StatePublished - 2019

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