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Michael A Park

Publications and source records attributed to Michael A Park.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
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Nearfield Summary and Analysis of the Third AIAA Sonic Boom Prediction Workshop C608 Low Boom Demonstrator

A summary and statistical analysis of the nearfield Computational Fluid Dynamics (CFD)submissions for the Third AIAA Sonic Boom Prediction Workshop is provided with a focus onthe C608 Low Boom Flight Test Demonstrator. The C608 is more complex in terms of geometryand propulsion boundary conditions than previous workshop cases and is more representativeof vehicles with lower ground loudness and the potential for lower annoyance. The nearfieldsignatures submitted by the participants are propagated to the ground to compute statisticsof loudness measures over the vehicle sonic boom carpet. Principle component analysis isused to extract the primary variation modes. Context from previous sonic boom workshopsindicates that this workshop has the lowest variation even though the case is more challengingbecause it is quieter and more complex. The results documented in this summary indicate thatthe international state-of-the-art for nearfield CFD has a variation that is small enough formeaningful low-boom design and analysis. Low-boom configuration analysis methods with lowvariation are important tools to develop certification processes for addressing the prohibitionon overland supersonic commercial flight.

sonic boom CFD workshop c608↗
NASA NTRSDate not supplied

Nearfield Anisotropic Mesh Adaptation for the Third AIAA Sonic Boom Workshop

Sonic boom prediction is critical for the development of low-boom supersonic aircraft and encouraging a replacement of the overland commercial supersonic ban with a certification standard. The Third AIAA Sonic Boom Workshop nearfield test cases provide a unique opportunity to review anisotropic adaptive-mesh strategies for complex geometries with important propulsion interaction effects. Anisotropic metrics formulated to control estimated Mach interpolation and integrated nearfield pressure signature (goal-oriented) errors are compared with the results obtained on workshop-provided meshes. Detailed flow solutions and mesh renderings are combined with computational schlieren images to reveal the complex interactions present in a shock-plume interaction wind tunnel model and a prototype of the Low-Boom Flight Demonstrator. A favorable comparison of independent implementations of the entire simulation process provides evidence that each process is implemented correctly and sets a solid foundation for confidence in the nearfield prediction of each method.

sonic boom↗
NASA NTRSDate not supplied

Verification of Viscous Goal-Based Anisotropic Mesh Adaptation

Adaptive unstructured mesh techniques have a limited, but growing impact on production analysis workflows where the control of discretization error is critical to obtaining reliable simulation results. Recent progress has matured a number of independent implementations of flow solvers, anisotropic metric construction methods, and anisotropic mesh adaptation mechanics. A key ingredient for the broader acceptance of unstructured mesh adaptation is the verification of these implementations. Anisotropic metric construction methods are evaluated with analytically defined primal fields and the corresponding entropy variables as adjoint fields. This allows the comparison of different metric formulations and different implementations of the same formulation without the complications of a flow and adjoint solution method. The convergence of the output associated with the entropy variable adjoint is studied for mesh adaptation to these fields and a manufactured solution. Mesh adapted drag output is studied for two simple wings in compressible laminar flow to show fine-mesh convergence of multiple metric construction methods to less than a single drag count. The documentation of these verification exercises helps to prepare these goal-based methods for routine use in more complex simulations for production workflows.

mesh adaptation↗
NASA NTRSDate not supplied

Boundary Representation Tolerance Impacts on Mesh Generation and Adaptation

The control of discretization error is critical to obtaining reliable simulation results. Re-cent progress has matured anisotropic mesh adaptation, which automates discretization error control for complex geometries. However, the meshing process can fail when geometric model Boundary REPresentation (BREP) tolerances are larger than boundary layer surface nor-mal and tangential spacing requirements. Geometry sources are often created in Mechanical Computer-Aided Design (MCAD) systems, which are designed to produce models for manufacturing and not the stricter requirements of viscous flow analysis. BREP tolerances are strained by three factors: the inherent complexity of the model (e.g., large range of scales and complex topology), the numerical difficulties arising from surface/surface intersections, and the omission of crucial data during export and translation. Manual preparation of geometry is commonly employed to enable expert-guided mesh generation, which severely inhibits work-flow automation. Accommodation of loose BREP tolerances is required for automated mesh processes, because barrier issues may not be detected until well into the solution process. To raise awareness of this class of geometry issues and their impact on simulation, a survey of these barrier issues is presented with example mitigation techniques. This awareness may also impact geometry creation workflows to prevent the introduction of these artifacts.

CAD↗
NASA NTRSDate not supplied

Multiscale Mesh Adaptation for Transonic Aeroelastic Flutter Problems

This work applies multiscale mesh adaptation with refine to reduce spatial discretization error of aeroelastic computational fluid dynamics (CFD) simulations. Benchmark flutter models, such as the pitch and plunge NACA64A-010 airfoil and the benchmark supercritical wing, are studied with both a linearized frequency-domain solver and time-marching CFD coupled to a modal structural solver in FUN3D. The undeformed NASA Common Research Model (CRM), an aeroelastic jig shape variant of the CRM, is also studied with the linearized frequency-domain approach. For these cases, the adaptation process converges to comparable flutter predictions to hand-generated meshes but with smaller node counts. However the additional disciplines of the linearized frequency-domain analysis, the mesh deformation, and the unsteady finite-volume solver create robustness challenges that need to be addressed before it can be applied as a fully automated process for complex transonic aeroelastic problems. In particular, negative volumes are observed to be an issue for FUN3D’s linear elasticity mesh deformation solver when moving the adapted meshes.

Aeroelasticity↗
NASA NTRSDate not supplied

Angle-of-Attack Sweep with Mesh Adaptation for High-Lift Configurations

This paper reports an angle-of-attack (alpha) sweep study with mesh adaptation for the high-lift configuration - JAXA Standard Model (JSM) from the 3rd AIAA High-Lift Prediction Workshop. The method of angle-of-attack (alpha) continuation, where the flow-field at a certain angle of attack is initialized from the solution obtained at the previous angle of attack, is applied to adapted unstructured meshes. Since the meshes are continuously adapted, flow-field initialization on a particular mesh for a certain angle is done through linear interpolation of the solution from the previous mesh. Interpolated initial conditions usually prevent massively separated solutions that may otherwise occur with impulsive initial conditions. Alpha continuations are done in both forward (increasing alpha) and reverse (decreasing alpha) directions, resulting in the formation of hysteresis loops. Skin frictions are compared with the wind-tunnel oil flow images and pressure coefficients are compared with the wind-tunnel values, at selected angles of attack. Final paper will include results also for the high-lift version of the Common Research Model (CRM-HL) from the 4th AIAA High-Lift Prediction Workshop. A thorough comparison of the results will also be made with the available wind-tunnel data.

Mesh Adaptation↗
NASA NTRSDate not supplied

Component-Based Development of CFD Software FUN3D

FUN3D, a suite of Computational Fluid Dynamics simulation and design tools developed at the NASA Langley Research Center, has undergone continuous development since the late1980s. It contains a large portion of legacy code. Extending it with new capabilities becomes increasingly difficult. To improve the extensibility and reusability, FUN3D is moving toward component-based development. New features, such as Stabilized Finite Elements, Yoga, and Sparse Linear Algebra Toolkit, are integrated into the system as components. Some existing features such as the Node-Centered Finite Volume Solver, are also being refactored to components. The integration of these components poses new requirements on the development workflow. In this paper, we describe the Continuous Integration of FUN3D to support component-based development, and discuss the tools used, the practices followed, and lessons learned during the transition from the traditional approach.

computational fluid dynamics software↗
NASA NTRSDate not supplied

Anisotropic Goal-Based Mesh Adaptation Metric Clarification and Development

Adaptive unstructured mesh techniques have a limited, but growing impact on production analysis workflows to control discretization error for reliable simulation results. Multiple independent implementations of flow solvers, anisotropic metric construction methods, and anisotropic mesh adaptation mechanics have matured. Goal-based metrics target estimated error in output functions, such as lift and drag, through the guidance of an adjoint solution. A unification of goal-based anisotropic metrics is presented for steady viscous flows, which is an active area of research. These goal-based metrics drive robust and efficient anisotropic mesh adaptation for the calculation of output functions. The super-convergent functional output error behavior of stabilized finite-element methods is exploited without a formal proof, and evidence of super-convergence is shown in numerical experiments. Mesh adapted drag and lift outputs for two simple bodies in compressible viscous flow show convergence of error to less than a single drag count. Asymptotic behavior established for relatively coarse meshes shows the efficiency of this goal-based metric when compared to solution interpolation error control and expert-guided meshing. Anisotropic mesh adaptation techniques are applied to a transport aircraft in a high-lift configuration where variation between approaches decreases with mesh refinement, but asymptotic behavior is not observed with available resources.

goal-based↗
NASA NTRSDate not supplied

The Influence of Adaptive Mesh Refinement on the Prediction of Vortex Interactions about a Generic Missile Airframe

The complex interaction of forebody and wing vortices significantly impacts missile aerodynamics. The formation of these vortices involves smooth regions of the geometry or geometric discontinuities like leading edges, trailing edges, tips, and corners. Regions of supersonic flow and complex shock topologies interact with boundary layers and vortices. Smooth-body separation and 3D viscous effects strain current Reynolds-averaged Navier-Stokes (RANS) techniques. The quantification and control of discretization error is critical to obtaining reliable simulation results and often turbulence model assessments are made in the presence of unquantified (and potentially large) discretization errors. Two mesh adaptation schemes are applied to steady RANS simulations. Multiscale unstructured mesh adaptation is applied to control interpolation error estimates of the Mach field, which resolves boundary layers, vortices, and shocks. A dual-mesh approach with overset communication is applied between an expert-crafted near-body unstructured mesh and an adaptive off-body Cartesian mesh refined with Q-criterion scaled by the strain tensor magnitude. A generic missile configuration is examined in a supersonic flow field to show the interaction of mesh adaptation and turbulence model. Turbulence model modifications for rotational correction and a quadratic constitutive relationship show a strong influence on adaptive mesh refinement and predicted rolling moment.

slender body aerodynamics↗
NASA NTRSDate not supplied

Wall-Modeled Large-Eddy Simulations for High-Lift Configurations using FUN3D

Wall-modeled large-eddy simulation (WMLES) capability has recently been implemented into FUN3D, an unstructured, node-centered, finite-volume solver developed at the NASA Langley Research Center. In this paper, WMLES is assessed for two configurations that are representative for high-lift applications. The first configuration is a nominal two-dimensional multielement airfoil that has been extensively studied in the literature. WMLES solutions are computed for four angles of attack and compared with previously reported solutions. Good agreement of integrated forces, surface pressures, and boundary-layer velocity profiles is shown with available experimental data especially at lower angles of attack. WMLES solutions are also computed for the NASA High-Lift Common Research Model over a large range of angles of attack. Forces, pitching moments, and pressure distributions are favorably compared with the experimental data up to the maximum lift, including the angle of attack where the maximum lift is obtained experimentally. Eddy visualization techniques of q-criterion and density-gradient magnitude illustrate the resolved content.

High-Lift flows↗
NASA NTRSDate not supplied

FUN3D Mesh Adaptation Simulations of 4th AIAA High-Lift Prediction Workshop Case 1a

Special sessions of the High Lift Prediction/Geometry & Mesh Generation Workshop. Will be written and presented at AIAA Aviation 2022. Describes in detail FUN3D Mesh adaptation simulation results for the 4th AIAA High-Lift Prediction Workshop. RANS (Stabilized Finite Element SA-neg) results for Case 1a are presented.

4th High-Lift Prediction Workshop Case 1a↗