FUN3D and CFL3D Computations for the First High Lift Prediction Workshop

Abstract

Two Reynolds-averaged Navier-Stokes codes were used to compute flow over the NASA Trapezoidal Wing at high lift conditions for the 1 st AIAA CFD High Lift Prediction Workshop, held in Chicago in June 2010. The unstructured-grid code FUN3D and the structured-grid code CFL3D were applied to several different grid systems. The effects of code, grid system, turbulence model, viscous term treatment, and brackets were studied. The SST model on this configuration predicted lower lift than the Spalart-Allmaras model at high angles of attack; the Spalart-Allmaras model agreed better with experiment. Neglecting viscous cross-derivative terms caused poorer prediction in the wing tip vortex region. Output-based grid adaptation was applied to the unstructured-grid solutions. The adapted grids better resolved wake structures and reduced flap flow separation, which was also observed in uniform grid refinement studies. Limitations of the adaptation method as well as areas for future improvement were identified.

NASA Trapezoidal Wing Computations Including Transition and Advanced Turbulence Modeling

“…The term "FT" in the table indicates fully turbulent, and the term "trans set" indicates that transition locations were fixed a priori, as described in Section II. Note that some of the listed computations were actually a part of the earlier study by Park et al, 12 but they are included here for comparison purposes.…”

“…All computations were performed on "medium" grid levels from the workshop grid refinement study. Grid study results for the UH6 and SX1 grids can be found in Park et al 12 The grids denoted as UH6 (without brackets) and UH16 (both with and without brackets) were unstructured mixed-element grids. SX1 (without brackets) was a structured multi-zone grid, and UX9 was the same grid written in unstructured format (hexahedra).…”

“…29 These codes were also used in an earlier study associated with HiLiftPW-1. 12 Transition is accounted for in two different ways: (1) by zeroing out turbulence production terms in laminar regions on each of the elements by using regions specified by Eliasson et al 17 (also provided on the HiLiftPW website), and (2) by employing the 4-equation γ-Re θ SST transition/turbulence model of Langtry and Menter. 21 In CFL3D and FUN3D, the default implementations of the production terms for the SST and γ-Re θ SST models make use of the "vorticity approximation," introduced by Menter 30 and referred to elsewhere b as "SST-V." In this approximation, the production term τ ij ∂u i /∂x j is replaced with µ t Ω 2 , where µ t is the eddy viscosity and Ω is the magnitude of vorticity.…”

“…[5][6][7][8][9][10][11][12][13][14][15][16][17][18] Most of these studies involved a few wellknown "standard" turbulence models such as Spalart-Allmaras (SA) 19 and Menter's shear-stress transport (SST) 20 applied in fully turbulent mode. At the workshop, SA (fully turbulent) was heavily favored because it tended to yield closer agreement to experiment for the Trapezoidal Wing.…”

Sonic-Boom Mitigation Through Aircraft Design and Adjoint Methodology

“…This code provides discretely consistent adjoint capabilities for sensitivity analysis. For many years, FUN3D has been used to perform adjoint-based mesh adaptation 9,10,11,12 and design optimization, 13,14 including optimization of the near-field sonic-boom waveforms, which represent the current state of the art in sonic boom mitigation. In the present paper, we are looking beyond the current state-of-the-art approaches to directly optimize ground-based sonic boom metrics rather than continue working on near-field target matching.…”