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Investigate the use of Discrete Patterned Roughness for Turbulent Transition Control in a Hypersonic Boundary Layer



OBJECTIVE: Model and investigate the use of discrete patterned roughness for turbulent transition control with rough surface conditions that result from manufacturing, or wear and ablation during hypersonic flight.

DESCRIPTION: Discrete patterned roughness has been successful in suppressing laminar-turbulent transition on hypersonic lift-generating configurations involving cross-flow. In these cases, the surfaces have been hydrodynamically smooth. Experiments are needed to evaluate the effect of rough surfaces on the transition control. This should involve experiments in multiple (at least two) quiet hypersonic wind tunnels. Test articles would be lift-generating geometries in which a cross-flow instability is the dominant mechanism of turbulent transition. These articles would include a number of documentable surface roughness conditions, including a baseline smooth surface. The roughness descriptions will be used in simulations of boundary layer turbulent transition with the experiments providing validation. These experiments will document the sensitivity of transition Reynolds number and the level of discrete roughness transition control on the background roughness. In the event of a reduction in transition control, approaches to overcome this should be proposed.Wind tunnel experiments at Mach 3.5 and 6.0 have demonstrated the ability of patterned discrete roughness to delay turbulence transition on lifting bodies where the dominant mechanism is through a cross-flow instability and is applicable to circular cones at angles of attack and elliptic cross-section cones such as the HiFiRE-5 (Hypersonic International Flight Research Experimentation Program) design. The approach is based on seeding less-amplified (subcritical) stationary cross-flow modes that suppress the growth of the more-amplified (critical) cross-flow modes, and thereby delay transition. Experiments on circular cones at angles of attack have increased the transition Reynolds number by as much as 40%. These experiments have been in idealized flows without extreme surface heating or ablation. The model surfaces were also highly polished so that the discrete roughness height or depth could be extremely small (O40µm). For transition control, the necessary roughness height or depth will depend on the background surface roughness. A more critical scale is the spacing between the discrete roughness that determines the spanwise wavenumber of the excited subcritical cross-flow modes. The background surface roughness spectrum will therefore be a factor.Given the number of benefits of delaying transition on hypersonic vehicles, and the successful demonstrations of this technology, investigation into realistic flight geometries with surface roughness that takes into account wear and ablation is needed. This would involve wind tunnel experiments in multiple quiet hypersonic tunnels. The surface roughness of the test articles should range from a baseline smooth (O40µm) surface to varying degrees of distributed roughness.Descriptions of the roughness could likely come from surface impressions of past flight test vehicles, or possibly surfaces generated on test articles placed in high-enthalpy hypersonic facilities. In all cases, the roughness needs to be quantified through highly resolved 3-D surface measurements. The roughness descriptions would be used in simulations that predict turbulence transition and will be validated through comparisons to the experiments. Ultimately for practical implementation, the sensitivity of the discrete roughness transition control on the level of background roughness needs to be determined. In the event that a reduction in transition control is observed, approaches that overcome the reduction need to be investigated.Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. owned and operated with no foreign influence as defined by DoD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence and Security Agency (DCSA). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this project as set forth by DCSA and SSP in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advanced phases of this contract.

PHASE I: Develop an initial concept design of a model geometry with cross-flow dominated laminar-turbulent transition and the generation of surface roughness representing pre-flight and post-flight conditions using a smooth surface to provide a baseline condition. Fabricate a model of a scale that will operate within the quiet zone of at least two quiet hypersonic wind tunnels. Employ wind tunnel conditions that are sufficient to achieve turbulent transition on the model, and roughness that is interchangeable, with documented characteristics.The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype solution in Phase II. Prepare a Phase II plan.

PHASE II: Fully develop a model for the effectiveness of discrete roughness to suppress turbulent transition and ensure the validation of test articles in wind tunnel tests that will involve a test article that is large enough to provide better measurement of spatial resolution and reduce edge effects. Use the quantitatively same background surface roughness from Phase I. For the different roughness cases, perform experiments that measure the turbulent transition location, verify that the mechanism of transition involves a cross-flow instability, and includes both surface visualization and off-wall measurements in 3-D space within the boundary layer. With the added spatial resolution of the larger model, place special emphasis on off-wall measurements within the boundary layer. Specifically focus experimentson interaction between stationary and traveling cross-flow modes, with the latter possibly energized by the higher disturbance levels produced by the roughness. Use these results to form the basis for the design of discrete roughness model to suppress turbulent transition.In addition to the experiments, develop simulations that are intended to be an analog to the wind tunnel experiments. Ensure that the simulations’ initial conditions match the experimental conditions, and include descriptions of the background roughness from Phase I. Compare the results of the simulationsdirectly with those in the experiments. Assuming experimental validation of the simulations, use it to further optimize the discrete roughness transition control. Prepare a Phase III development plan to transition the technology for Navy use and potential commercial use.It is probable that the work under this effort will be classified under Phase II (see Description section for details).

PHASE III: Conduct necessary qualification testing of the laminar-transition control method to merit further investment and consideration for military HV platforms. Work together with an OEM (original equipment manufacturer) to develop a business plan and seek necessary investment to support the product/process/service for the OEM military provider. This effort may have application to reentry vehicles operated by NASA or other organizations in addition to vehicles operating at trans-sonic and supersonic velocities.

KEYWORDS: Hypersonic Vehicles, Laminar-Turbulent Transition, Transition Control, Surface Roughness, Wind Tunnel, Transition Reynolds Number


1. Corke, T.,A.,E and Semper, M. “Control of stationary cross-Flow modes in a mach 6 boundary layer using patterned roughness.” J. Fluid Mech., 856, 2018, pp. 822-849. DOI: 2. Schuele, C.Y. Corke, T. and Matlis, E. “Control of Stationary Cross-Flow Modes in a Mach 3.5 Boundary Layer Using Patterned Passive and Active Roughness.” J. Fluid Mech., 718, 2013, pp. 5-38. DOI:

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