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The use of differential equations such as Eikonal, Hamilton-Jacobi, and Pnisson for the economical calculation of the nearest (normal) wall distance d, which is needed by some turbulence models, is explored. Modifications that could palliate some turbulence-modeling anomalies are also discussed. Economy is of especial value for deforming/adaptive grid problems. For these, ideally, d is repeatedly computed. It is shown that the Eikonal and Hamilton-Jacobi equations can be easy to implement when written in implicit (or iterated) advection and advection-diffusion equation analogous forms, respectively. These, like the Poisson Laplacian term, are commonly occurring in computational-fluid-dynamics (CFD) solvers, allowing the reuse of efficient algorithms and code components. The use of the NASA CFL3D CFD program to solve the implicit Eikonal and Hamilton-Jacobi equations is explored. The reformulated d equations are easy to implement and are found to have robust convergence. For accurate Eikonal solutions, upwind metric differences are required. The Poisson approach is also found effective and easiest to implement. Hence this method is recommended. Modified distances are not found to affect global outputs such as lift and drag significantly, at least in common situations such as airfoil flows.

The modeled configuration of three-dimensional thin-layer Navier-stokes computations for F/A-18 configuration includes a precise surface representation of the fuselage, leading-edge extension (LEX) and wing, with or without the leading wind deflection. The computational flowfield domain around the subject configuration is decomposed using the multiblock structured grid strategy. The compressible Navier-stokes equations with an upwind-biased, flux difference splitting approach is solved by an algorithm, and the steady state solutions determined.

A multidisciplinary gradient-based sensitivity-analysis methodology is evaluated for optimization of rotorcraft configurations. The tightly coupled discipline models include physics-based fluid dynamics and rotorcraft comprehensive analysis. A discretely consistent adjoint method accounts for sensitivities of the unsteady flow and unstructured, dynamic, overset grids; whereas sensitivities of structural responses to aerodynamic loads are computed using a complex-variable method. The methodology is applied to optimize the shape of UH-60A Blackhawk helicopter blades for hover and forward-flight conditions. The objective of the multipoint design is to simultaneously increase the rotorcraft figure of merit in hover flight and reduce the rotor power in forward flight. Trimmed loose-coupling solutions for the baseline configuration are used to initiate the tight-coupling multidisciplinary analysis. The target thrust, rolling moment, and pitching moment are enforced as optimization constraints. The optimized configuration improves the optimization metrics at both design points. The improved performance and all constraints are maintained over many revolutions beyond the optimization interval, satisfying the required flight conditions. The computational cost of the optimization cycle is assessed in a high-performance computing environment and found affordable for design of rotorcraft in general level-flight conditions. [ABSTRACT FROM AUTHOR]

A multidisciplinary sensitivity analysis of rotorcraft simulations involving tightly coupled high-fidelity computational fluid dynamics and comprehensive analysis solvers is presented and evaluated. A sensitivity-enabled fluid-dynamics solver and a nonlinear flexible multibody-dynamics solver are coupled to predict aerodynamic loads and structural responses of helicopter rotor blades. A discretely consistent adjoint-based sensitivity analysis available in the fluid-dynamics solver provides sensitivities arising from unsteady turbulent flows and unstructured dynamic overset meshes, whereas a complex-variable approach is used to compute structural sensitivities with respect to aerodynamic loads. The multidisciplinary sensitivity analysis is conducted through integrating the sensitivity components from each discipline of the coupled system. Sensitivities of lift computed by the multidisciplinary sensitivity analysis are verified by comparison with the sensitivities obtained by complex-variable simulations. The multidisciplinary sensitivity analysis is applied to a constrained gradient-based design optimization for a HART-II rotorcraft configuration. [ABSTRACT FROM AUTHOR]