126 research outputs found
System Effects in Identifying Risk-Optimal Data Requirements for Digital Twins of Structures
Structural Health Monitoring (SHM) technologies offer much promise to the
risk management of the built environment, and they are therefore an active area
of research. However, information regarding material properties, such as
toughness and strength is instead measured in destructive lab tests. Similarly,
the presence of geometrical anomalies is more commonly detected and sized by
inspection. Therefore, a risk-optimal combination should be sought,
acknowledging that different scenarios will be associated with different data
requirements. Value of Information (VoI) analysis is an established statistical
framework for quantifying the expected benefit of a prospective data collection
activity. In this paper the expected value of various combinations of
inspection, SHM and testing are quantified, in the context of supporting risk
management of a location of stress concentration in a railway bridge. The Julia
code for this analysis (probabilistic models and influence diagrams) is made
available. The system-level results differ from a simple linear sum of marginal
VoI estimates, i.e. the expected value of collecting data from SHM and
inspection together is not equal to the expected value of SHM data plus the
expected value of inspection data. In summary, system-level decision making,
requires system-level models
Building a Practical Natural Laminar Flow Design Capability
A preliminary natural laminar flow (NLF) design method that has been developed and applied to supersonic and transonic wings with moderate-to-high leading-edge sweeps at flight Reynolds numbers is further extended and evaluated in this paper. The modular design approach uses a knowledge-based design module linked with different flow solvers and boundary layer stability analysis methods to provide a multifidelity capability for NLF analysis and design. An assessment of the effects of different options for stability analysis is included using pressures and geometry from an NLF wing designed for the Common Research Model (CRM). Several extensions to the design module are described, including multiple new approaches to design for controlling attachment line contamination and transition. Finally, a modification to the NLF design algorithm that allows independent control of Tollmien-Schlichting (TS) and cross flow (CF) modes is proposed. A preliminary evaluation of the TS-only option applied to the design of an NLF nacelle for the CRM is performed that includes the use of a low-fidelity stability analysis directly in the design module
Grid-Adapted FUN3D Computations for the Second High Lift Prediction Workshop
Contributions of the unstructured Reynolds-averaged Navier-Stokes code FUN3D to the 2nd AIAA CFD High Lift Prediction Workshop are described, and detailed comparisons are made with experimental data. Using workshop-supplied grids, results for the clean wing configuration are compared with results from the structured code CFL3D Using the same turbulence model, both codes compare reasonably well in terms of total forces and moments, and the maximum lift is similarly over-predicted for both codes compared to experiment. By including more representative geometry features such as slat and flap brackets and slat pressure tube bundles, FUN3D captures the general effects of the Reynolds number variation, but under-predicts maximum lift on workshop-supplied grids in comparison with the experimental data, due to excessive separation. However, when output-based, off-body grid adaptation in FUN3D is employed, results improve considerably. In particular, when the geometry includes both brackets and the pressure tube bundles, grid adaptation results in a more accurate prediction of lift near stall in comparison with the wind-tunnel data. Furthermore, a rotation-corrected turbulence model shows improved pressure predictions on the outboard span when using adapted grids
Status of Turbulence Modeling for Hypersonic Propulsion Flowpaths
This report provides an assessment of current turbulent flow calculation methods for hypersonic propulsion flowpaths, particularly the scramjet engine. Emphasis is placed on Reynolds-averaged Navier-Stokes (RANS) methods, but some discussion of newer meth- ods such as Large Eddy Simulation (LES) is also provided. The report is organized by considering technical issues throughout the scramjet-powered vehicle flowpath including laminar-to-turbulent boundary layer transition, shock wave / turbulent boundary layer interactions, scalar transport modeling (specifically the significance of turbulent Prandtl and Schmidt numbers) and compressible mixing. Unit problems are primarily used to conduct the assessment. In the combustor, results from calculations of a direct connect supersonic combustion experiment are also used to address the effects of turbulence model selection and in particular settings for the turbulent Prandtl and Schmidt numbers. It is concluded that RANS turbulence modeling shortfalls are still a major limitation to the accuracy of hypersonic propulsion simulations, whether considering individual components or an overall system. Newer methods such as LES-based techniques may be promising, but are not yet at a maturity to be used routinely by the hypersonic propulsion community. The need for fundamental experiments to provide data for turbulence model development and validation is discussed
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