Effects of Surface Roughness Patterns on Hypersonic Boundary-layer Stability and Transition

This effort will characterize the effects of selected roughness, gap, and other surface defect modalities on laminar-to-turbulent transition at hypersonic speeds on baseline geometries as well as a Navy-relevant configuration with fins to be selected in consultation with the program managers. The end result, in a comprehensive program over Phase II Base and Phase II Option, will be a methodology for analyzing, both computationally and via low-disturbance hypersonic wind tunnel experiments, specific roughness/defect patterns and predicting/measuring their effect on transition. Specific products will include a critical assessment of roughness effects on transition mechanisms pertinent to a relevant geometry with features to include at least one fin, scaling methodology to relate subscale wind tunnel experiment to flight, impact at selected critical roughness locations, wind tunnel noise and parametric effects such as (for example) nose bluntness and angle of attack. SE partner Purdue University will measure and characterize roughness/gap/flaw patterns from Navy-provided material samples and specify the representative defect properties to be reproduced in wind tunnel models to be fabricated by SE for evaluation in the low-disturbance Purdue BAM6QT. SE partner NIA/ NASA will compute the stability characteristics of selected basic state(s) as well as the receptivity to selected roughness patterns for this effort. The team will evaluate these features experimentally at Mach 6 and computationally at Mach 6 and other Mach numbers specified by the Navy sponsors as relevant. Pending funding, progress, and facility availability, additional analysis may include: 1) the effects of blowing/gas injection to simulate ablative mass transfer, potentially in conjunction with roughness; 2) experimental evaluation of different Mach numbers; and/or 3) inputs into flight experiment design (e.g., MACH-TB).Ā In Phase II Option the developed approach will be extended to predict, fabricate, and analyze roughness patterns capable of suppressing relevant instabilities that may lead to transition.