Description:
TECHNOLOGY AREA(S): Materials
OBJECTIVE: Localized heating may produce profile disruptions in air vehicles at high enough velocities to affect either/both structural integrity and trajectory. The topic seeks to model the effects of such disruptions over a range of velocities and conditions.
DESCRIPTION: The proposed effort studies potential damage mechanisms resulting in mission failure. Localized heating may result in holes/pockets (0.5 inch diameter or greater) and/or local structural instabilities especially at the leading edge regions of assets at high enough velocities to affect either/both structural integrity and trajectory. The topic seeks to model the effects of such disruptions on performance of air vehicles over a range of velocities and conditions. Well before burn through or back surface temperature effects on internal components, mechanical failure and/or profile disruption of structural materials may result in mission failure. For example, the induced flutter in softening or vaporized constituent materials for various boundary flow velocity profiles may amplify damage area induced by Directed Energy irradiation. Furthermore, at high enough mach numbers a simple hole/pocket, e.g., at 0.5 inch diameter or greater, may be enough to induce difficulty in maintaining trajectory. Structural fluttering and ablation can be modeled using coupled micro/macro techniques to study the effects of instabilities directly induced by irradiation and/or amplified by aerothermal heating and acoustic loads present at especially leading edge regions. A flow boundary layer is critical to structural instability simulation, as the energy and momentum transfer from within the boundary layer drive the continuing deformation and flutter of the illuminated region, extending into the original structural profile and against the protrusions as the cyclic deformation proceeds. For associated models, velocities, structural features, and damage initiation and development should be considered. Computational Fluid Dynamics (CFD) can be employed to develop environment predictions, including extreme hypersonic environments; e.g., industrial developments at Dassault (France) include turbulence, high temperatures, dissociation, radiation, energy transport, and slip flows in association with the Hermes space plane in 2D and 3D [1], currently embedded in an industrial stabilized finite element code including Reynolds-Averaged Navier-Stokes (RANS) turbulence, Detached Eddy Simulation, higher-order elements, and chemically reacting flows as part of the European project IDIHOM (Industrialisation of High-Order Methods) aimed at bringing higher-order capabilities to industrial applications, tested by project partners e.g. on a 3D Falcon jet geometry [2]. CFD is required for flutter prediction associated with transonic flows (shock waves, separation), especially for military applications with associated complex configurations requiring unstructured meshes [3]. Stabilized methods for unstructured meshes applied to turbulent flows are critical for such modeling, e.g. [4]. The aerodynamic/acoustic forces associated with development of holes/pockets will cause torques on the vehicle that especially at high mach numbers could cause loss of trajectory to target, as well as the potential for local heating effects especially in the case of associated thermal protection material systems (TPS) disruptions leading to amplified profile disruption through the structural instability mechanisms already mentioned. Material types can be any layered TPS (i.e. materials systems enhancing esp temperature environment survivability) including specifically high-temperature ceramics and and/or polymers (and may include others) appropriate to vehicles traveling at velocities where the effects will be of consequence, generally suggesting hypersonics but the range of applicable velocities is of interest so a variety of material types and velocities are possible, with higher mach number systems being most likely to be affected. The modeling can be used as well for informing countermeasures based on materials properties, adaptivity, coating protective systems, etc., which could also be part of the study. An aerospace prime contractor partner is encouraged for structural, flight control and mission-relevant details. Government-Furnished Equipment and data are not required.
PHASE I: A modeling capability should be demonstrated that will realistically lead to combining flow velocity with profile features to assess effects on structural integrity and trajectory.
PHASE II: A full analysis capability shall assess the effects of hole diameters and pockets, of various size and shape within realistic parameters, on flutter, propagating damage, and aerothermal heating of various layered material systems at especially high mach numbers, but over a range of velocity profiles as determined by the analyses and supporting data as may exist. Direct testing of model systems in wind tunnels or other relevant conditions is encouraged as may be possible.
PHASE III: Potential long range military and commercial air platforms as well as government and commercial space vehicles must survive potential disruptions at relevant conditions of velocity and temperature and relevant data and countermeasures are lacking.
REFERENCES:
1. Shiau, L. C., Lu, L. T. (1990), "Nonlinear flutter of composite laminated plates," Mathl Comput. Modelling, 14, 983-988
2. Dolvin, D. J. (2008), "Hypersonic International Flight Research and Experimentation (HIFiRE) - Fundamental Sciences and Technology Development Strategy," Paper AIAA-2008-2581, 15th AIAA International Space Planes and Hypersonic Systems and Technologies Conference 28 April - 1 May 2008, Dayton, O
3.https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system
KEYWORDS: Heating, Profile, TPS, Flutter, Trajectory
