High Lift Prediction Workshop Research Articles

Aerodynamic Prediction of the High-Lift Common Research Model with Modified Turbulence Model

Aerodynamic simulations were carried out in the study presented in this paper focusing on the stall performance of the High-Lift Common Research Model obtained from the fourth AIAA High-Lift Prediction Workshop. Various turbulence models of Reynolds-averaged Navier–Stokes simulations are analyzed. A modified version of the transitional k−v2¯−ω model was developed to enhance stall prediction accuracy for high-lift configurations with a nacelle chine. The vortex generator, three-element airfoil, and high-lift model are numerically simulated. The results reveal that implementing a k−v2¯−ω model with the separation shear layer fixed notably enhances the stall prediction behavior for both the three-element airfoil and high-lift configuration without affecting the prediction of the vortex strength of a vortex generator. Moreover, incorporating rotation correction into the SPF k−v2¯−ω model improves the prediction of vortex strength and further enhances stall prediction for the high-lift configuration. The relative error in predicting the maximum lift coefficient is less than 5% of the experimental data. The study also investigated the impact of the nacelle chine on the stall behavior of the high-lift configuration. The results demonstrate that the chine vortex can mitigate the adverse effects of the nacelle/pylon vortex system and increase the maximum lift coefficient.

Summary of the 4th High-Lift Prediction Workshop Hybrid RANS/LES Technology Focus Group

This paper summarizes the collective efforts of multiple teams that contributed to the hybrid RANS/LES technical focus group for the 4th AIAA CFD High Lift Prediction Workshop (HLPW-4), which took place on January 7, 2022, in San Diego, California. The overall conclusion is that turbulence-resolving methods such as hybrid RANS/LES (HRLES) do offer improved predictions for these high-lift geometries, with respect to the underlying RANS models, but there are nuances, and some unresolved issues remain that should be the focus of future work. In particular, while HRLES methods appear to show clearly improved predictions at higher angles of attack, there is some tendency for HRLES methods to return slightly worse moment predictions at lower angles of attack, suggesting that prediction of the shallow separation from the flaps might need further research. Computing cost also remains a significant issue, with HRLES methods requiring roughly nine times more high-performance computing central processing unit core hours than steady-state RANS methods, indicating that future algorithmic and computational optimization could be beneficial. Finally, there are strong indications that modeling the wind tunnel has a positive impact on correlation with experimental measurements, suggesting that future work might be better focused on in-tunnel simulations.

Fourth AIAA High-Lift Prediction Workshop: Fixed-Grid Reynolds-Averaged Navier–Stokes Summary

The current state-of-the-practice technology for high-lift aerodynamic simulations is to solve the Reynolds-averaged Navier–Stokes (RANS) equations on a fixed grid or a refinement sequence of fixed grids. The Fixed-Grid Reynolds-Averaged Navier–Stokes Technology Focus Group set out to determine meshing requirements and best practices, whether RANS can accurately predict the change in aerodynamic performance with changes in flap deflection, whether RANS modeling can produce accurate results near CLmax, and the effects of underconvergence and solution strategy on computed results. Eighteen groups of participants submitted over 100 datasets. Challenges with grid convergence and iterative convergence made it impossible to definitively answer all the questions we had posed. Despite this, we can conclude that meshes with at least half a billion cells (more than one billion degrees of freedom) are required for grid convergence away from stall; that RANS simulations cannot currently be reliably used to predict aerodynamic coefficients near stall, nor changes in coefficients with changes in flap angle; that iterative underconvergence remains a significant source of uncertainty in outputs; and that solution initialization can have an important effect on solution behavior, including flow separation patterns.

FFVHC-ACE: Fully Automated Cartesian-Grid-Based Solver for Compressible Large-Eddy Simulation

This study presents a fully automated Cartesian-grid-based compressible flow solver, named FrontFlow/Violet Hierarchical Cartesian for Aeronautics based on Compressible-flow Equations (FFVHC-ACE), for large-eddy simulation (LES) and its aeronautical applications. FFVHC-ACE enables high-fidelity LES of high-Reynolds-number flows around complex geometries by adopting three key numerical methods: hierarchical Cartesian grids, wall modeling in LES, and the kinetic-energy and entropy preserving (KEEP) scheme. The hierarchical Cartesian grids allow fully automated grid generation for complex geometries in FFVHC-ACE, and high-fidelity LES of high-Reynolds-number flows around complex geometries is realized by the wall modeling and the KEEP scheme on the non-body-fitted hierarchical Cartesian grids. We apply FFVHC-ACE to wall-modeled LES around high-lift aircraft configurations at wind-tunnel-scale Reynolds number and real-flight Reynolds number , demonstrating the capability of FFVHC-ACE for fully automated grid generation and high-fidelity simulations around complex aircraft configurations. The computed flowfield and aerodynamic forces at the wind-tunnel-scale Reynolds number agree well with the experimental data provided in the past AIAA High Lift Prediction Workshop (Rumsey et al., Journal of Aircraft, Vol. 56, No. 2, 2019, pp. 621–644). Furthermore, the wall-modeled LES at the real-flight Reynolds number shows good agreement of the lift coefficient with flight-test data.

HLPW-4: Wall-Modeled Large-Eddy Simulation and Lattice–Boltzmann Technology Focus Group Workshop Summary

A summary of the nine submissions to the Wall-Modeled Large-Eddy Simulation and Lattice–Boltzmann (WMLESLB) Technical Focus Group (TFG) at the 4th High lift Prediction Workshop is provided. The focus of this TFG was to assess the current capabilities of WMLES and LB methods on a complex high-lift configuration across a wide range of angles of attack. Analysis of the submitted data suggests that >250  M spatial degrees of freedom are needed to accurately predict pitching moments at high angles of attack due to large pressure gradients present on the outboard slat and main element for α>17° (corrected for free-air). While some scatter is reported in pitching moment coefficient at the low-angles of attack (α<11°), excellent agreement is observed between submissions near the CL,max state. Objective superiority of WMLES methods over Reynolds-averaged Navier–Stokes (RANS) can be seen in terms of lack of excess outboard separation; a majority of the WMLES and LB submissions predict wedge-shaped separation patterns consistent with the experimental oil flow. The in-tunnel simulations show excellent agreement with the experiment in terms of a) integrated loads, b) surface flow-topology, and c) mechanism for the onset of inboard stall. Further evidence is provided to demonstrate both qualitative and quantitative superiority of the WMLES submissions over RANS.

Fourth High-Lift Prediction/Third Geometry and Mesh Generation Workshops: Overview and Summary

The Fourth AIAA Computational Fluid Dynamics (CFD) High Lift Prediction Workshop and the Third Geometry and Mesh Generation Workshop were held collaboratively with the common goal of assessing the numerical prediction capability of current-generation computational fluid dynamics technology for swept medium-/high-aspect-ratio wings in high-lift configurations. A key aspect of this joint endeavor was the use of technology focus groups: an innovative new approach for workshops involving close collaboration between participants. These groups, which included both mesh-generation and flow-solver experts, worked to accelerate advancements for their particular methodologies by addressing key questions of importance before the workshop. The high-lift version of the NASA Common Research Model (CRM-HL) configuration was the focus of this workshop. Measured experimental wind-tunnel data were available for comparison. The workshop also included a two-dimensional turbulence model verification exercise based on the CRM-HL wing shape. Altogether, 44 participants submitted a total of 184 datasets of CFD results. This paper provides a high-level summary of the results and conclusions from the workshop. Like at past workshops, fixed-grid Reynolds-averaged Navier–Stokes methods continued to be inaccurate and inconsistent for predicting high-lift flow physics near maximum lift conditions. However, mesh adaptation definitively brought more consistency. Scale-resolving methods appeared most promising for predicting high-lift flow physics near maximum lift.

High Order Wall-Modeled Large-Eddy Simulation on Mixed Unstructured Meshes

In the present study, an algebraic equilibrium wall model previously developed for hexahedral elements is extended to handle mixed meshes including prismatic, tetrahedral, and pyramidal elements in the context of a discontinuous high-order method. This extension is needed for complex geometries, for which high-order mixed elements (e.g., tetrahedral and pyramidal elements) are often necessary near solid walls to avoid meshing challenges. Various design decisions are discussed to achieve the best performance on massively parallel CPU/GPU architectures for a production-level high-order large-eddy simulation solver based on the flux reconstruction/correction procedure via reconstruction method, hpMusic. The extension to other elements is first evaluated using a benchmark channel flow problem at various Reynolds numbers. After that, flow over the NASA high-lift Common Research Model (CRM-HL) from the 4th AIAA High-lift Prediction Workshop is computed to further test the new implementation. Computational results at the third- and fourth-order accuracies are compared with experimental data.

Implicit large Eddy simulation of the NASA CRM high-lift configuration near stall

Recent progress in adaptive high-order numerical methods, high-order mesh generation, and scalable implicit time integration approaches has made large eddy simulation (LES) more affordable than ever before. In the present study, we demonstrate the progress by performing implicit LES of a benchmark problem from the 3rd AIAA High-Lift Prediction Workshop: NASA's Common Research Model (CRM) high-lift configuration. The LES tool, hpMusic, is based on the flux reconstruction method capable of handling high-order mixed unstructured meshes. P-refinement studies are used to assess the mesh-dependence of the numerical solutions. Comparisons are also made with available experimental data, and a very good agreement was obtained in lift and drag coefficients between the present computation and wall-corrected experimental data.

Simulations of Aerodynamic Separated Flows Using the Lattice Boltzmann Solver XFlow

We present simulations of turbulent detached flows using the commercial lattice Boltzmann solver XFlow (by Dassault Systemes). XFlow’s lattice Boltzmann formulation together with an efficient octree mesh generator reduce substantially the cost of generating complex meshes for industrial flows. In this work, we challenge these meshes and quantify the accuracy of the solver for detached turbulent flows. The good performance of XFlow when combined with a Large-Eddy Simulation turbulence model is demonstrated for different industrial benchmarks and validated using experimental data or fine numerical simulations. We select five test cases: the Backward-facing step the Goldschmied Body the HLPW-2 (2nd High-Lift Prediction Workshop) full aircraft geometry, a NACA0012 under dynamic stall conditions and a parametric study of leading edge tubercles to improve stall behavior on a 3D wing.

Effects of boundary layer transition on the aerodynamic analysis of high-lift systems

Transition to turbulence is known as a factor that impacts the performance of high-lift devices, but only a few numerical results that include transition are available in the literature. We use the Langtry-Menter γ−Reθ transition model to study the influence of transition to turbulence in global aerodynamic coefficients and flow topology in three-dimensional high-lift configurations. The influence of turbulence inflow variables is also addressed. Numerical results are compared with previous results obtained with the Shear Stress Transport (SST) turbulence model, which does not account for transition effects. The numerical simulations are performed using configuration “one” from the 1st AIAA CFD High-Lift Prediction Workshop. Experimental data from the NASA Langley 14 by 22-ft Subsonic Wind Tunnel provide the global aerodynamic information for the verification of our numerical results. It is observed that the inclusion of transition to turbulence impacts the flow topology, as well as the aerodynamic coefficients.

High-Lift Simulations of the Japan Aerospace Exploration Agency Standard Model

The Japan Aerospace Exploration Agency standard model high-lift configuration was analyzed computationally using both the OVERFLOW and LAVA codes for the third AIAA High-Lift Prediction Workshop. Simulations were performed both with and without the nacelle/pylon feature as prescribed by the workshop test cases. Without the nacelle/pylon, evidence of multiple solutions was observed when a quadratic constitutive relation was used in the turbulence modeling; however, time-accurate simulations seemed to favor one solution over the other. With the nacelle/pylon, no evidence of multiple solutions was observed. Laminar–turbulent transition modeling was also applied to the configuration, and it had an overall favorable impact on the lift predictions.

Verification and Validation of OpenFOAM for High-Lift Aircraft Flows

This paper presents a detailed investigation into the performance of the open-source finite volume computational fluid dynamics (CFD) code OpenFOAM for complex high-lift aircraft flows. A range of cases are investigated, including a zero-pressure gradient flat plate, a NACA0012 airfoil at varying angles of attack, a DSMA661 airfoil, a NASA High-Lift Common Research Model, and a Japan Aerospace Exploration Agency (JAXA) standard model (JSM) high-lift aircraft model. The final three cases were computed as part of the third AIAA High Lift Prediction Workshop. For all of these, the same mesh and turbulence model is used to benchmark against the commercial CFD code STAR–CCM+. The paper shows that OpenFOAM using the Spalart–Allmaras model matches the lift and drag coefficient within 3% of the commercial code for all the test cases simulated. For the JSM high-lift aircraft for which experimental data is available, both codes show good agreement at prestall angles of attack but fail to capture the location of separation at poststall angles, even though the global lift appears to be well predicted. Although OpenFOAM demonstrated comparable accuracy to a range of CFD codes for these aforementioned test cases, further work is required to improve the robustness and stability of OpenFOAM for these types of flows.

JAXA’s and KHI’s Contribution to the Third High Lift Prediction Workshop

This paper is based on results presented at the Third High Lift Prediction Workshop. The Japan Aerospace Exploration Agency provided computer-aided design models and experimental results of the Japan Aerospace Exploration Agency Standard Model to the workshop as a test case. An unstructured hybrid mesh generator, MEGG3D, was applied to the Japan Aerospace Exploration Agency Standard Model wing-body and wing-body-nacelle-pylon configurations to generate grids, which were provided for the use of workshop participants by the committee. This paper presents details of experimental results and the method for deforming the computer-aided design models and volume grids based on the experiment. The Japan Aerospace Exploration Agency and Kawasaki Heavy Industries, Ltd., performed computational fluid dynamics simulations of the test case as workshop participants. Kawasaki Heavy Industries also generated custom participant-generated grids. Their computational results using the TAS code and Cflow are discussed.

Overview and Summary of the Third AIAA High Lift Prediction Workshop

The Third AIAA CFD High Lift Prediction Workshop was held in Denver, Colorado, in June 2017. The goals of the workshop continued in the tradition of the first and second high-lift workshops: 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 two different configurations, a “clean” high-lift version of the NASA Common Research Model, and the Japan Aerospace Exploration Agency Standard Model. The former was a CFD-only study because experimental data were not available before the workshop. The latter was a nacelle/pylon installation study that included comparison with experimental wind-tunnel data. The workshop also included a two-dimensional turbulence model verification exercise. Thirty-five participants submitted a total of 79 data sets of CFD results. A variety of grid systems (both structured and unstructured) as well as different flow simulation methodologies (including Reynolds-averaged Navier–Stokes and lattice Boltzmann) were used. This paper analyzes the combined results from all workshop participants. A statistical summary of the CFD results is also included.

Mechanism/structure/aerodynamic multidisciplinary optimization of flexible high-lift devices for transport aircraft

Mission adaptive variable camber wing in both chord-wise and span-wise directions that can improve the aerodynamic performance during takeoff, landing and cruising flight, will be the state-of-the-art high-lift system for next generation airliners. Based on NASA TrapWing model released on the 1st AIAA CFD High-lift Prediction Workshop, a smart high-lift system with “Flexible Droop Nose & Single Slotted Hinge Flap combined with spoiler deflection & Flexible Trailing Edge Flap” is proposed in this paper. The Flexible Droop Nose is actuated by kinematic chains mechanism, the Single Slotted Hinge Flap is actuated by simple hinge mechanism and the Flexible Trailing Edge Flap is actuated by link/track mechanism.A mechanism/structure/aerodynamic multidisciplinary optimization platform based on iSIGHT software is constructed for this smart high-lift system. This platform consists of stress analysis, high-lift configuration generation, high-lift configuration structure grid generation, computational fluid dynamics and optimization algorithm modules. The optimal takeoff and landing configurations with comprehensive performance of mechanism, aerodynamic and structure is then obtained after multidisciplinary optimization. Finally, the CFD results show that the aerodynamics performance of this smart high-lift system is more effective than the original NASA TrapWing model.

Flow Analysis of the DLR-F11 High-Lift Model Using the Galatea-I Code

The academic computational fluid dynamics code Galatea-I is used in this study for the prediction of the flow over the DLR-F11 high-lift configuration, presented in the Second AIAA High-Lift Prediction Workshop. The proposed solver employs the Reynolds-averaged Navier–Stokes equations, modified appropriately by the artificial compressibility method and combined with the shear-stress transport turbulence model to account for the simulation of incompressible turbulent flows. Attention is mainly directed toward the assessment of the alternative, artificial compressibility methodology against such test cases because the majority of the workshop participants had implemented compressible Reynolds-averaged Navier–Stokes codes with preconditioning matrices instead. To this end, the flow at various angles of attack over the DLR-F11 aircraft model is studied, whereas the obtained results are compared to the available experimental data as well as simulation results produced by reference solvers. A satisfactory agreement is reported, demonstrating the proposed methodology’s potential to accurately predict such complex flows and adapt to uncommon areas of use.

EFD-CFD 비교워크샵 목적과 발전 방향

EFD-CFD 비교워크샵은 AIAA의 Drag Prediction Workshop과 High Lift Prediction Workshop을 참고하여 국내의 풍동실험과 전산해석기술 수준을 향상시키고 두 분야의 협력을 통해 공기역학의 기술수준을 고양하고자 조직되었다. 국내외에서 수행된 3개의 풍동실험 Case에 대한 전산해석 수행 및 비교분석을 수행하며 2015년부터 비교 워크샵이 개최되고 있다. 향후 국내 연구자들의 참여와 협력을 적극 유도하며 새로운 형상에 대한 실험과 해석 및 분석을 진행하여 국내 공기역학의 기술발전에 기여하고자 한다. EFD-CFD Comparison Workshop was proposed based on the drag prediction workshop and high lift prediction workshop of AIAA. This workshop is organized to escalate the levels of wind tunnel test and computational fluid dynamics and to escalate the level of domestic aerodynamic technology through the collaboration of both areas. For three benchmark cases of which wind tunnel test results are available, comparison workshops have been held since 2015.

Japan Aerospace Exploration Agency Studies for the Second High-Lift Prediction Workshop

This paper summarizes Japan Aerospace Exploration Agency studies using a structured grid solver UPACS and an unstructured grid solver TAS-code for the second AIAA CFD High-Lift Prediction Workshop test cases and follow-on problems. Computations are performed for the grid convergence study using the configuration without any slat tracks and flap track fairings on a series of multi-block structured grids and a series of unstructured grids provided by the High Lift Prediction Workshop committee. In this paper, the following are mainly discussed: 1) grid convergence verification study of the turbulence models using a two-dimensional bump case, 2) grid convergence studies for Spalart–Allmaras and shear stress transport turbulence models using UPACS, 3) change of grid convergence and predicted flow fields with and without a nonlinear quadratic constitutive relation model for Spalart–Allmaras and shear stress transport turbulence models using UPACS including evaluation at higher angles of attack, and 4) comparison studies using different solvers UPACS and TAS on different grid systems with and without the quadratic constitutive relation model for the Spalart–Allmaras model.

Lattice Boltzmann Method Contribution to the Second High-Lift Prediction Workshop

This paper presents the results of the computational-fluid-dynamics code XFlow for the test case proposed in the 2nd High-Lift Prediction Workshop. The target of this international workshop is to assess the accuracy of numerical predictions provided by a wide selection of computational-fluid-dynamics codes and applied to the aeronautical industry. It deals with a full aircraft in high-lift configuration with unstowed flap and slat, including slat tracks, flap track fairings, and slat pressure tube bundles. XFlow is a particle-based kinetic solver, based on the lattice Boltzmann method. It is well suited for such low-speed flows because the standard lattice Boltzmann method is limited to low Mach number. It employs large-eddy simulation turbulence modeling with the wall-adapting local eddy model, coupled with a generalized law of the wall to model the boundary-layer prediction. Traditional computational-fluid-dynamics software requires a time-consuming meshing process that is prone to errors, which significantly affects the mesh quality and thus the outcome of a simulation. Furthermore, the complex geometries such as elements in small gaps add an extra complication to generate the mesh. In contrast, the method employed by XFlow avoids the traditional meshing process using an octree structure, with spatial refinement related by a factor of 2 based on the input geometry. The discretization stage is strongly accelerated, thus reducing engineering costs and complex geometry computations are affordable in a straightforward way. The research presented in this paper starts with a grid validation study (case 1) with the DLR F11 geometry in configuration 2. Because the lattice Boltzmann method approach used by XFlow simplifies the integration of geometrical details, the full polar characteristic is directly investigated with configuration 5 (case 3) that includes the actual model configuration on the aerodynamic performances. The configuration 5 geometry includes slat tracks and flap track fairings, as well as slat pressure tube bundles. This is the highest-fidelity geometry in comparison with wind-tunnel testing. This study is conducted for both low- and high-Reynolds-number conditions, 1.35 and 15.1 million, respectively. In addition, the study focuses on the poststall region and the influence of geometrical details on turbulence and flow patterns. The interest for the poststall region is justified by the lack of consistency in the stall prediction found during the 2nd AIAA High-Lift Prediction Workshop by all the participants.

NSU3D Results for the Second AIAA High-Lift Prediction Workshop

Simulation results for the second AIAA CFD High-Lift Prediction Workshop using the unstructured computational fluid dynamics code NSU3D are presented. The solution algorithms employed in NSU3D for this study are described along with examples of convergence history and computational cost. The geometry used for the simulation consists of the DLR-F11 wing–body with high-lift system deployed in a landing configuration. This geometry is representative of a modern transport aircraft high-lift system that has been tested experimentally over a suitable Reynolds number range. Results are presented from two sets of computational studies, the first performed at the University of Wyoming using standard workshop unstructured meshes, and the second performed at Bombardier Aerospace using in-house-generated meshes. In both cases, results are presented for two different turbulence models, allowing an assessment of the sensitivity of the results to grid densities, grid types, and turbulence models. Results consist of computed force and moment coefficients across a range of angles of attack and for two different Reynolds numbers, as well as surface pressure profiles and off-body velocity profiles, all of which are compared with experimental data. The results compare favorably with experimental data and generally fall within the standard deviation of the workshop collective results. Computations using the Spalart–Allmaras turbulence model tend to overpredict the maximum lift value and incidence, while results using the model tend to underpredict the maximum lift value. The best agreement in terms of force coefficients is observed with the turbulence model using the Bombardier internally generated meshes.