Anthony J. Sclafani

A Wing-Body Fairing Design for the DLR-F6 Model: A DPW-III Case Study

The work presented herein has been performed in preparation of the Third AIAA CFD Drag Prediction Workshop to be held June, 2006 at the AIAA 24 th Applied Aerodynamics conference in San Francisco, California. The purpose of this work is to provide a new test case to address a problematic issue related to the inability for the industry-wide state-of-the-art CFD to achieve asymptotic grid convergence for cases with moderate-to-large amounts of flow separation. Two wing-body fairings have been designed for the DLR-F6 model geometry. The first fairing greatly alleviates the side-of-body separation near the wing upper-surface trailing-edge, while the second fairing has completely removed this separation bubble. These geometries will be made available for public release, although only the second fairing will be a subject of study in the next workshop.

Overview and Summary of the Second AIAA High Lift Prediction Workshop

The second AIAA CFD High-Lift Prediction Workshop was held in San Diego, California, in June 2013. The goals of the workshop continued in the tradition of the first high-lift workshop: to assess the numerical prediction capability of current-generation computational fluid dynamics (CFD) technology for swept, medium/high-aspect-ratio wings in landing/takeoff (high-lift) configurations. This workshop analyzed the flow over the DLR-F11 model in landing configuration at two different Reynolds numbers. Twenty-six participants submitted a total of 48 data sets of CFD results. A variety of grid systems (both structured and unstructured) were used. Trends due to grid density and Reynolds number were analyzed, and effects of support brackets were also included. This paper analyzes the combined results from all workshop participants. Comparisons with experimental data are made. A statistical summary of the CFD results is also included.

Drag Prediction for the NASA CRM Wing-Body-Tail Using CFL3D and OVERFLOW on an Overset Mesh

In response to the fourth AIAA CFD Drag Prediction Workshop (DPW-IV), the NASA Common Research Model (CRM) wing-body and wing-body-tail configurations are analyzed using the Reynolds-averaged Navier-Stokes (RANS) flow solvers CFL3D and OVERFLOW. Two families of structured, overset grids are built for DPW-IV. Grid Family 1 (GF1) consists of a coarse (7.2 million), medium (16.9 million), fine (56.5 million), and extra-fine (189.4 million) mesh. Grid Family 2 (GF2) is an extension of the first and includes a superfine (714.2 million) and an ultra-fine (2.4 billion) mesh. The medium grid anchors both families with an established build process for accurate cruise drag prediction studies. This base mesh is coarsened and enhanced to form a set of parametrically equivalent grids that increase in size by a factor of roughly 3.4 from one level to the next denser level. Both CFL3D and OVERFLOW are run on GF1 using a consistent numerical approach. Additional OVERFLOW runs are made to study effects of differencing scheme and turbulence model on GF1 and to obtain results for GF2. All CFD results are post-processed using Richardson extrapolation, and approximate grid-converged values of drag are compared. The medium grid is also used to compute a trimmed drag polar for both codes.

CFL3D/OVERFLOW Results for DLR-F6 Wing/Body and Drag Prediction Workshop Wing

A series of overset grids was generated in response to the Third AIAA CFD Drag Prediction Workshop (DPW-III) which preceded the 25th Applied Aerodynamics Conference in June 2006. DPW-III focused on accurate drag prediction for wing/body and wing-alone configurations. The grid series built for each configuration consists of a coarse, medium, fine, and extra-fine mesh. The medium mesh is first constructed using the current state of best practices for overset grid generation. The medium mesh is then coarsened and enhanced by applying a factor of 1.5 to each (I, J, K) dimension. The resulting set of parametrically equivalent grids increase in size by a factor of roughly 3.5 from one level to the next denser level. Computational fluid dynamics simulations were performed on the overset grids using two different Reynolds-averaged Navier-Stokes flow solvers: CFL3D and OVERFLOW. The results were postprocessed using Richardson extrapolation to approximate grid-converged values of lift, drag, pitching moment, and angle of attack at the design condition. This technique appears to work well if the solution does not contain large regions of separated flow (similar to that seen in the DLR-F6 results) and appropriate grid densities are selected. The extra-fine grid data helped to establish asymptotic grid convergence for both the OVERFLOW FX2B wing/body results and the OVERFLOW DPW-W1/W2 wing-alone results. More CFL3D data are needed to establish grid convergence trends. The medium grid was used beyond the grid convergence study by running each configuration at several angles of attack so drag polars and lift/pitching moment curves could be evaluated. The alpha sweep results are used to compare data across configurations as well as across flow solvers. With the exception of the wing/body drag polar, the two codes compare well qualitatively showing consistent incremental trends and similar wing pressure comparisons.

Extended OVERFLOW Analysis of the NASA Trap Wing Wind Tunnel Model

The OVERFLOW computational fluid dynamics code is used to simulate a high lift flow field about the NASA Trap Wing wind tunnel model with the goal of better understanding bracket and boundary layer transition effects on prediction of aerodynamic loads. This study is a continuation of the 1 AIAA CFD High Lift Prediction Workshop analysis. Following a set of lessons learned from the workshop, improvements in grid and flow solver inputs are first implemented to establish a new baseline dataset for a bracket-off configuration analyzed with a fully turbulent boundary layer. Brackets are added to the grid system and regions of laminar flow are modeled using two approaches: 1) Spalart-Allmaras (SA) turbulence model coupled with fixed transition and 2) Shear Stress Transport (SST) turbulence model coupled with the Langtry-Menter -Re transition model. The findings suggest that the effects of brackets and transition on computed lift are nearly equal in magnitude and opposite in sign up to an angle-of-attack of 21. Comparisons with experiment are made using results from the LaRC 14x22 wind tunnel test including velocity probe data.

DPW-5 Analysis of the CRM in a Wing-Body Configuration Using Structured and Unstructured Meshes

*† ‡ § ** †† ‡‡ Two general purpose Reynolds Averaged Navier-Stokes (RANS) flow solvers, OVERFLOW and BCFD, are used to analyze the NASA Common Research Model (CRM) in a wing-body configuration. The codes are run on structured and unstructured common grid families built specifically for the 5 th AIAA CFD Drag Prediction Workshop (DPW-5) allowing for meaningful comparison of data. There are six grid sizes in the family ranging from a 0.6 million cell “Tiny” mesh up to a 138 million cell “Super-Fine” mesh. Results from a grid convergence study are evaluated for each solver and grid type with focus on isolating individual effects of turbulence model and differencing scheme on computed forces, moments and wing pressures. A “Medium” mesh consisting of 5.1 million cells is used to run the wing-body configuration through an angle-of-attack sweep as part of a buffet onset study. The solutions are used to better understand variations in high speed wing separation prediction driven by the strengthening shock and by corner flow physics at the wing-body juncture. Numerical simulation of side-of-body separation continues to be a challenge for RANS methods where solutions are sensitive to grid density and turbulence model, amongst other variables. However, a newly developed quadratic constitutive relation (QCR) is employed with favorable results. Two additional studies are conducted to: a) investigate how well common grid solutions compare with those on a grid built using best practices for a given flow solver, and b) quantify the effects of transition and wing twist to provide additional corrections needed for comparisons of CFD results with experimental data.

RANS Technology for Transonic Drag Prediction; A Boeing Perspective of the 4th Drag Prediction Workshop

The Common Research Model utilized by the fourth Drag Prediction Workshop was employed to investigate the accuracy of three primary codes used at Boeing for transonic aerodynamic ow analysis. The codes used in this study are CFL3D (block structured), OVERFLOW (overset structured), and BCFD (unstructured). Solutions were obtained for the wing-body con guration with the horizontal tail at incidence angles of 0◦, +2◦, −2◦ and with the tail removed. Grid convergence and resolution, mesh topology, and turbulence models were considered the primary factors in this study for accurate predictions of cruise drag, pitching moments, and Reynolds number e ects. Also, these factors were considered in wing and tail side-of-body ow separation predictions. In this study, all three cases (one required and two optional) were completed with all three codes. The solutions were obtained with the one-equation turbulence model of Spalart & Allmaras and the twoequation SST turbulence model of Menter. For the trim drag and Reynolds number e ect studies (optional cases), OVERFLOW and BCFD were run only with the Spalart-Allmaras turbulence model.

Analysis of the Common Research Model Using Structured and Unstructured Meshes

Two general-purpose Reynolds-averaged Navier–Stokes flow solvers, OVERFLOW and BCFD, are used to analyze the NASA Common Research Model in a wing–body configuration. The codes are run on structured and unstructured common-grid families built specifically for the Fifth AIAA CFD Drag Prediction Workshop, allowing for a meaningful comparison of data. The results from a grid-convergence study are evaluated for each solver and grid type with focus on isolating individual effects of turbulence model and differencing scheme on computed forces, moments, and wing pressures. A medium mesh consisting of 5.1 million cells is used for a buffet-onset study to better understand variations in high-speed wing-separation prediction driven by the strengthening shock and by corner-flow physics at the wing–body juncture. Numerical simulation of side-of-body separation continues to be a challenge for Reynolds-averaged Navier–Stokes methods, in which solutions are sensitive to grid density and turbulence model, among other vari...

Drag Prediction for the Common Research Model Using CFL3D and OVERFLOW

In response to the fourth AIAA CFD Drag Prediction Workshop, the NASA Common Research Model wing–body and wing–body–tail configurations are analyzed using the Reynolds-averaged Navier–Stokes flow solvers CFL3D and OVERFLOW. Two families of structured, overset grids are built. Grid Family 1 consists of a coarse (7.2 million), medium (16.9 million), fine (56.5 million), and extra-fine (189.4 million) mesh. Grid Family 2 is an extension of the first and includes a super-fine (714.2 million) and an ultra-fine (2.4 billion) mesh. The medium grid anchors both families with an established build process for accurate cruise drag prediction studies. This base mesh is coarsened and enhanced to form a set of parametrically equivalent grids that increase in size by a factor of roughly 3.4 from one level to the next denser level. Both CFL3D and OVERFLOW are run on Grid Family 1 using a consistent numerical approach. Additional OVERFLOW runs are made to study effects of differencing scheme and turbulence model on Grid F...

Reynolds-Averaged Navier–Stokes Technology for Transonic Drag Prediction: A Boeing Perspective

The Common Research Model used by the Fourth Drag Prediction Workshop was employed to investigate the accuracy of three primary codes used at The Boeing Company for transonic aerodynamic flow analysis. The codes used in this study are CFL3D (block structured), OVERFLOW (overset structured), and BCFD (unstructured). Solutions were obtained for a wing/body configuration, with the horizontal tail at incidence angles of 0, +2, −2  deg, and with the tail removed. Grid convergence and resolution, mesh topology, and turbulence models were considered the primary factors in this study for accurate predictions of cruise drag, pitching moments, and Reynolds number effects. Also, these factors were considered in wing and tail side-of-body flow separation predictions. In this study, all three cases (one required and two optional) were completed with all three codes. The solutions were obtained with the one-equation turbulence model of Spalart and Allmaras and the two-equation shear-stress transport turbulence model of...