James M. Luckring

Connection between leading-edge sweep, vortex lift, and vortex strength for delta wings

An effort is made to clarify the effect of leading-edge sweep on the vortex lift and leading-edge vortex strength of a slender wing; while it is often assumed that increasing sweep enhances vortex lift and strength, the opposite is the case. The suction analogy is used in association with numerical and experimental data to derive simple formulas yielding the actual relationship for delta wings. The difference between vortex lift and nonlinear lift is highlighted.

Uncertainty in Computational Aerodynamics

J. M. Luckring, M. J. Hemsch , J. H. MorrisonAerodynamics, Aerothermodynamics, and Acoustics CompetencyNASA Langley Research CenterHampton, VirginiaABSTRACTAn approach is presented to treat computationalaerodynamics as a process, subject to the fundamentalquality assurance principles of process control andprocess improvement. We consider several aspectsaffecting uncertainty for the computationalaerodynamic process and present a set of stages todetermine the level of management required to meetrisk assumptions desired by the customer of thepredictions•CA

Navier-Stokes solutions about the F/A-18 forebody-LEX configuration

Three-dimensional viscous flow computations are presented for the F/A-18 forebody-LEX geometry. Solutions are obtained from an algorithm for the compressible Navier-Stokes equations which incorporates an upwind-biased, flux-difference-splitting approach along with longitudinally-patched grids. Results are presented for both laminar and fully turbulent flow assumptions and include correlations with wind tunnel as well as flight-test results. A good quantitative agreement for the forebody surface pressure distribution is achieved between the turbulent computations and wind tunnel measurements at a free-stream Mach number of 0.6. The computed turbulent surface flow patterns on the forebody qualitatively agree well with in-flight surface flow patterns obtained on an F/A-18 aircraft at a free-stream Mach number of 0.34.

Application of a patched-grid algorithm to the F/A-18 forebody-leading-edge extension configuration

A patched-grid algorithm for the analysis of complex configurations with an implicit, upwind-biased NavierStokes solver is presented. Results from both a spatial-flux and a time-flux conservation approach to patching across zonal boundaries are presented. A generalized coordinate transformation with a biquadratic geometric element is used at the zonal interface in order to treat highly stretched viscous grids and arbitrarily shaped zonal boundaries. Applications are made to the F/A-18 forebody-leading-edge extension configuration at subsonic, high-alpha conditions. Computed surface flow patterns compare well with ground-based and flight-test results; the large effect of Reynolds number on the forebody flowfield is shown.

Towards a Credibility Assessment of Models and Simulations

*† ‡ § ** †† A scale is presented to evaluate the rigor of modeling and simulation (M&S) practices for the purpose of supporting a credibility assessment of the M&S results. The scale distinguishes required and achieved levels of rigor for a set of M&S elements that contribute to credibility including both technical and process measures. The work has its origins in an interest within NASA to include a “Credibility Assessment Scale” in development of a NASA standard for models and simulations.

What Was Learned in Predicting Slender Airframe Aerodynamics with the F16-XL Aircraft

The CAWAPI-2 coordinated project has been underway to improve CFD predictions of slender airframe aerodynamics. The work is focused on two flow conditions and leverages a unique flight data set obt ...

Numerical and Theoretical Considerations for the Design of the AVT-183 Diamond-Wing Experimental Investigations

A diamond-wing configuration has been developed to isolate and study blunt-leadingedge vortex separation with both computations and experiments. The wing has been designed so that the results are relevant to a more complex Uninhabited Combat Air Vehicle concept known as SACCON. The numerical and theoretical development process for this diamond wing is presented, including a view toward planned wind tunnel experiments. This work was conducted under the NATO Science and Technology Organization, Applied Vehicle Technology panel. All information is in the public domain.

Multiblock Navier-Stokes solutions about the F/A-18 wing-LEX-fuselage configuration

Three-dimensional thin-layer Navier-Stokes computations are presented for the F/A-18 configuration. The modeled configuration includes an accurate surface representation of the fuselage, leading-edge extension (LEX), and wing, both with and without leading-edge flap deflection. A multiblock structured grid strategy is employed to decompose the computational flowfield domain around the subject configuration. Steady-state solutions are obtained from an algorithm that solves the compressible Navier-Stokes equations with an upwind-biased, fluxdifference splitting approach. The results presented are based on a fully turbulent flow assumption, simulating the high Reynolds number flow conditions that correspond to a recent F/A-18 flight experiment. Good agreements between the computations and the flight test results are obtained for both surface flow patterns as well as surface pressure distributions. Furthermore, a correlation between the computed LEX vortex-core and the flight test results, observed by way of smoke visualization, is also presented.

Flow Analysis of the F-16XL Aircraft (CAWAPI-2) At Transonic Flow Conditions

In the framework of the Cranked-Arrow Wing Aerodynamics Project International 2 (CAWAPI-2), a cooperation between Cassidian/EADS (Germany), KTH (Sweden), Lockheed-Martin (USA), NASA Langley (USA) and National Aerospace Laboratory NLR (The Netherlands) to further assess Computational Fluid Dynamics codes against F-16XL flight test data, National Aerospace Laboratory NLR performed an analysis of a set of transonic flight conditions available in the CAWAP 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 CFD analysis a transonic flight condition without deflected control surfaces was judged desirable by the CAWAPI-2 members. Therefore, it was decided to search the CAWAP database for a transonic flight condition without any control surface deflections. Since no information on the control surface deflections of the other transonic flight conditions was available to the CAWAPI-2 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 NLR’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 thus is much better suited for further comparisons between flight test data and CFD simulations.

A Reduced-Complexity Investigation of Blunt Leading-Edge Separation Motivated by UCAV Aerodynamics

A reduced complexity investigation for blunt-leading-edge vortical separation has been undertaken. The overall approach is to design the fundamental work in such a way so that it relates to the aerodynamics of a more complex Uninhabited Combat Air Vehicle (UCAV) concept known as SACCON. Some of the challenges associated with both the vehicle-class aerodynamics and the fundamental vortical flows are reviewed, and principles from a hierarchical complexity approach are used to relate flow fundamentals to system-level interests. The work is part of roughly 6-year research program on blunt-leading-edge separation pertinent to UCAVs, and was conducted under the NATO Science and Technology Organization, Applied Vehicle Technology panel.