Cranked-Arrow Wing Aerodynamics Project International Research Articles

Introduction to the Special Section on F-16XL Flight Aerodynamics Predictions at a High Angle of Attack

A third and final international project has been completed for the assessment of state-of-the-art computational fluid dynamics (CFD) capabilities to predict flight data obtained with an F-16XL aircraft. This work built upon two prior campaigns associated with the Cranked Arrow-Wing Aerodynamics Project International (CAWAPI). The second CAWAPI project, CAWAPI-2, focused on predictions for low-speed/high-angle-of-attack and transonic/low-to-moderate angle-of-attack conditions, and eight papers from this effort were published in Volume 54, Issue 2, of the Journal of Aircraft.

Synthesis of Hybrid Computational Fluid Dynamics Results for F-16XL Aircraft Aerodynamics

A synthesis is presented of recent numerical predictions for the F-16XL aircraft flowfields and aerodynamics. The computational analyses were all performed with hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation formulations, with an emphasis on unsteady flows and associated aerodynamics, and results from five computational methods are included. The work focused on one particular low-speed high angle-of-attack flight-test condition, and comparisons against flight-test data are included. This work represents the third coordinated effort using the F-16XL aircraft, and a unique flight-test dataset, to advance the knowledge of slender airframe aerodynamics as well as the capability for predicting these aerodynamics with advanced computational fluid dynamics formulations. The prior efforts were identified as the Cranked-Arrow Wing Aerodynamics Project International.

F-16XL Hybrid Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation on Unstructured Grids

The Cranked-Arrow Wing Aerodynamics Project International investigation is continued with the FUN3D and USM3D flow solvers to fuse flight test, wind-tunnel test, and simulation of swept-wing aerodynamic features. Simulations of a low-speed, high-angle-of-attack condition are compared: detached-eddy simulation, modified delayed detached-eddy simulation, and the Spalart–Allmaras Reynolds-averaged Navier–Stokes model. Isosurfaces of criterion show the development of coherent primary and secondary vortices on the upper surface of the wing that spiral, burst, and commingle. Mean detached-eddy simulation and modified delayed detached-eddy simulation pressures better predict the flight-test measurements than Spalart–Allmaras model predictions, especially on the outer-wing section. The USM3D simulations predicted many sharp tones in volume point pressure spectra with low broadband noise, and the FUN3D simulations predicted more broadband noise with weaker tones. Spectra of the volume points near the outer-wing leading edge were primarily broadband for both codes. Time-averaged forces are very similar between FUN3D simulations and between USM3D simulations, but FUN3D predicts slightly higher lift and lower drag than USM3D. There is more variation in the pitching moment predictions. Spectra of the unsteady forces and moment are mostly broadband for FUN3D and tonal for USM3D simulations.

Flow Analysis of the F-16XL Aircraft at Transonic Flow Conditions

In the framework of the Cranked-Arrow Wing Aerodynamics Project International 2, Netherlands National Aerospace Laboratory performed an analysis of a set of transonic flight conditions available in the Cranked-Arrow Project database. Flight condition FC70 was used previously during the Cranked-Arrow Wing Aerodynamics Project International to investigate transonic flow on the F-16XL aircraft. During this project, it was discovered that flight condition FC70 was flown with a deflected leading-edge flap. To facilitate computational fluid analysis, a transonic flight condition without deflected control surfaces was judged desirable by the Cranked-Arrow Project members. Therefore, it was decided to search the Cranked-Arrow Project database for a transonic flight condition without any control surface deflections. Because no information on the control surface deflections of the other transonic flight conditions was available to the Cranked-Arrow Project partners, an alternative approach to scrutinize the available flight-test sectional surface pressure measurements for indications of control surface deflections was adopted. This analysis revealed that flight condition FC79 was the most likely transonic flight condition to be flown without any control surface deflections. Flight conditions FC70 and FC79 were analyzed using National Aerospace Laboratory’s in-house-developed flow simulation system ENFLOW. Comparison of the measured and simulated surface pressure coefficients confirmed that flight condition FC79 was flown without any control surface deflections, and that this flight condition is thus much better suited for further comparisons between flight-test data and computational fluid dynamics simulations.

Computational Fluid Dynamics Predictions of Control-Surface Effects for F-16XL Aircraft

Computational fluid dynamics methods play an increasingly important role in aircraft design and development. Some examples are conditions that cannot be tested before a flight test. To rely on these methods, it is essential that they are assessed and evaluated with a state-of-the-art wind tunnel test and/or in-flight data. In a previous project, Cranked-Arrow Wing Aerodynamics Project International, it was reported that all computational fluid dynamics methods failed to some degree in the transonic regime where shock–vortex interaction phenomena were present. Detailed analysis of surface pressure distribution showed that computational fluid dynamics was not able replicate the correct flowfield and produce acceptable results. This paper aims to restudy those transonic flight conditions for which computational fluid dynamics underperforms and to try to determine or shed light on the extent to which surface effects contribute to the computational fluid dynamics predictions.

Overview of the Cranked-Arrow Wing Aerodynamics Project International

This paper provides a brief history of the F-16XL-1 aircraft, its role in the High-Speed Research Program, and how it was morphed into the Cranked-Arrow Wing Aerodynamics Project. Various flight, wind-tunnel, and computational fluid dynamics data sets were generated as part of the project. These unique and open flight data sets for surface pressures, boundary-layer profiles, and skin-friction distributions, along with surface flow data, are described and sample data comparisons are given. This is followed by a description of how the project became internationally known as Cranked-Arrow Wing Aerodynamics Project International and is concluded by an introduction to the results of a four-year computational predictive study of data collected at flight conditions by participating researchers.

F16-XL Geometry and Computational Grids Used in Cranked-Arrow Wing Aerodynamics Project International

The objective of the Cranked-Arrow Wing Aerodynamics Project International was to allow a comprehensive validation of computational fluid dynamics methods against the Cranked-Arrow Wing Aerodynamic ...

Reynolds-Averaged Navier-Stokes Solutions for the CAWAPI F-16XL Using Different Hybrid Grids

Ten groups participating in the Cranked Arrow Wing Aerodynamics Project International (CAWAPI) within the NATO-RTO task group AVT 113 have contributed viscous simulations of a full scale model of the F-16XL aircraft at different flight conditions. Three different classes of grids have been used by the different participants: a common structured grid, a common unstructured grid, and so-called individually tailored grids, which have been used by four participants: Lockheed Martin Aeronautics Company, University of Tennessee, Boeing Phantom Works, and EADS Military Air Systems. This paper focuses on the use of these individually generated grids. The different grid generation techniques and strategies (nonadapted, manually adapted, and solution-based adapted) are discussed and the solutions obtained in these individually tuned grids are compared with flight test data for different test cases.

Lessons Learned from Numerical Simulations of the F-16XL Aircraft at Flight Conditions

Nine groups participating in the Cranked Arrow Wing Aerodynamics Project International (CAWAPI) project have contributed steady and unsteady viscous simulations of a full-scale, semi-span model of the F-16XL aircraft. Three different categories of flight Reynolds/Mach number combinations were computed and compared with flight-test measurements for the purpose of code validation and improved understanding of the flight physics. Steady-state simulations are done with several turbulence models of different complexity with no topology information required and which overcome Boussinesq-assumption problems in vortical flows. Detached-eddy simulation (DES) and its successor delayed detached-eddy simulation (DDES) have been used to compute the time accurate flow development. Common structured and unstructured grids as well as individually-adapted unstructured grids were used. Although discrepancies are observed in the comparisons, overall reasonable agreement is demonstrated for surface pressure distribution, local skin friction and boundary velocity profiles at subsonic speeds. The physical modeling, steady or unsteady, and the grid resolution both contribute to the discrepancies observed in the comparisons with flight data, but at this time it cannot be determined how much each part contributes to the whole. Overall it can be said that the technology readiness of CFD-simulation technology for the study of vehicle performance has matured since 2001 such that it can be used today with a reasonable level of confidence for complex configurations.