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Document type:
Zeitschriftenaufsatz 
Author(s):
Hein, Stefan; Theiss, Alexander; Di Giovanni, Antonio; Stemmer, Christian; Schilden, Thomas; Schröder, Wolfgang; Paredes, Pedro; Choudhari, Meelan M.; Li, Fei; Reshotko, Eli 
Title:
Numerical Investigation of Roughness Effects on Transition on Spherical Capsules 
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. 
Journal title:
Journal of Spacecraft and Rockets 
Year:
2019 
Journal volume:
56 
Journal issue:
Pages contribution:
388-404 
Covered by:
Scopus 
Fulltext / DOI:
Publisher:
American Institute of Aeronautics and Astronautics (AIAA) 
E-ISSN:
0022-46501533-6794 
Accepted:
18.09.2018 
Date of publication:
29.01.2019 
TUM Institution:
Lehrstuhl für Aerodynamik und Strömungsmechanik