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Experimental Investigation of Roughness Effects on Transition on Blunt Spherical Capsule ShapesThe present contribution reviews recent experimental results of roughness effects on boundary layer transition on capsule geometries with spherical windward geometries. Experiments in three wind tunnel facilities are considered. The ACE Tunnel of Texas AM University, USA, provided Mach 6 experiments with distributed roughness at relatively low Reynolds numbers, 2.5 · 10(exp 5) < Re(sub d) < 5 · 10(exp 5), with d denoting the capsule diameter. The observed boundary layer transition compared well with correlations based on transient growth theory, even though the roughness heights were in the order of boundary layer thickness. Larger Reynolds numbers, 1 · 10(exp 6) < Re(sub d) < 3·10(exp 6), could be assessed in the hypersonic Ludwieg tube, HLB, of TU Braunschweig, Germany. Transition is observed at rather low, subcritical roughness values in the order of 20 μm for a roughness patch placed about the geometric center of the capsule model. These experiments varied fluctuation levels of the freestream. The authors assume that the observed transitions that occur downstream of the subcritical roughness patch are due to freestream disturbances in the tunnel, which interact with small roughness heights. Additional experiments in the HLB facility with patches of larger roughness height support the relevance of transient growth theory for low-to-medium roughness heights, relative to boundary layer thickness. The effects of Reynolds numbers and total flow enthalpy on transition with isolated roughness were investigated in the HIEST facility of JAXA, Japan. Here, a model insert with roughness elements of varying height for tripping transition to turbulence was employed. The results are compared to known trip effectiveness correlations for isolated roughness. Overall, the transient growth correlation seems to represent roughness-induced transition behavior on the ACE and HLB entry capsule shapes with roughness over the entire capsule surface. These experiment are however for perfect gases. Comparable experiments on roughness induced transition in a high-enthalpy facility are still needed to confirm the validity of transient-growth correlation for vehicle design.
Document ID
20180007671
Acquisition Source
Johnson Space Center
Document Type
Other
External Source(s)
Authors
Radespiel, Rolf
(Technische Universität Braunschweig Braunschweig, Germany)
Ali, Syed R. C.
(Technische Universität Braunschweig Braunschweig, Germany)
Bowersox, Rodney
(Texas A&M Univ. College Station, TX, United States)
Leidy, Andrew
(Texas A&M Univ. College Station, TX, United States)
Tanno, Hideyuki
(Kakuda Research Center Japan)
Kirk, Lindsay C.
(NASA Johnson Space Center Houston, TX, United States)
Reshotko, Eli
(Case Western Reserve Univ. Cleveland, OH, United States)
Date Acquired
November 13, 2018
Publication Date
August 1, 2018
Publication Information
Publication: Benchmarks in Multidisciplinary Optimization and Design for Affordable Military Vehicles
Publisher: Science and Technology Organization
ISBN: 978-92-837-2186-4
Subject Category
Aerodynamics
Report/Patent Number
STO-TR-AVT-240
JSC-E-DAA-TN60438
Funding Number(s)
OTHER: JA-0597-1
OTHER: DFG HYPTRANS PAK742
CONTRACT_GRANT: EOARD FA9550-16-1-0285
Distribution Limits
Public
Copyright
Public Use Permitted.
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