Abstract:The F-16XL flight vehicle has been used extensively to study the aerodynamics of medium-to high-angle-of-attack flight. Flight-test data, including surface pressures, are available for a wide range of flight conditions, allowing direct comparison between computational fluid dynamics and full-scale flight data. The most recent comprehensive study, made possible by NASA, was conducted by NATO Task Group AVT-113 and had participants from many different countries. One of the conclusions of the study was that unste… Show more
“…An example is shown in Fig. 67 from Morton and McDaniel (132) using the KESTREL code (119) with AMR. Grids were adapted in both space and time, and a very fine resolution of the wing vortex flowfield was achieved.…”
Section: Three-dimensional Flows Sharp or Blunt-leading-edge Vorticementioning
High-speed aircraft often develop separation-induced leading-edge vortices and vortex flow aerodynamics. In this paper, the discovery of separation-induced vortex flows and the development of methods to predict these flows for wing aerodynamics are reviewed. Much of the content for this article was presented at the 2017 Lanchester Lecture and the content was selected with a view towards Lanchester’s approach to research and development.
“…An example is shown in Fig. 67 from Morton and McDaniel (132) using the KESTREL code (119) with AMR. Grids were adapted in both space and time, and a very fine resolution of the wing vortex flowfield was achieved.…”
Section: Three-dimensional Flows Sharp or Blunt-leading-edge Vorticementioning
High-speed aircraft often develop separation-induced leading-edge vortices and vortex flow aerodynamics. In this paper, the discovery of separation-induced vortex flows and the development of methods to predict these flows for wing aerodynamics are reviewed. Much of the content for this article was presented at the 2017 Lanchester Lecture and the content was selected with a view towards Lanchester’s approach to research and development.
“…The unsteady flow simulations from CAWAPI-2 indicated that more detailed unsteady work with finer grid resolution held out promise for simulating the FC-25 case, and it became the focus for the CAWAPI-3 investigations with hybrid RANS-LES modeling. [54]; left, butt line 153.5 computed time mean and variation pressure profiles and flight data [55].…”
Section: Rans Simulationmentioning
confidence: 99%
“…The CAWAPI-3 Assessment studied this question further with hybrid RANS/LES simulations [2], and Fig. 15 summarises one set of the results of Morton and McDaniel [54]. Figure 15. CAWAPI-3 Hybrid RANS/LES simulations, FC-25.…”
In the early era of aviation, Frederick Lanchester was both an inventor and a theoretician driven by the need for a theory of flight that would reduce the guesswork in designing new aircraft. His book Aerodynamics in 1907 laid down the early foundations of such a theory. The theory with contributions from others, notably Ludwig Prandtl, was refined to become the basis for the sleek designs of WWII aircraft brought about with little guesswork. New technology changed aircraft design radically with the increased speed of jet propulsion reaching into the transonic range with nonlinear aerodynamics. In the late 1940s and early 1950s substantial guesswork returned to aircraft design. The legacy of Lanchester et al., however, lived on with the development of computational fluid dynamics (CFD) that could guide designers through nonlinear transonic effects. This article presents a historical sketch of how CFD developed, illustrated with examples explaining some of the difficulties overcome in the design of the first-generation swept-wing transonic fighters. The historical study is forensic CFD in search for the likely explanation of the designer’s choice for the wing shape that went into production a long time ago. The capability of current CFD applied to the aerodynamics of aircraft with slender wings is surveyed. The cases discussed involve flow patterns with coherent vortices over hybrid wings and wings of moderate sweep. Vortex-flow aerodynamics pertains to understanding the interaction of concentrated vortices with aircraft components. Modern Reynolds-Averaged Navier-Stokes (RANS) technology is useful to predict attached flow. But vortex interaction with other vortices and breakdown lead to unsteady, largely separated flow which has been found out of scope for RANS. Direct simulation of the Navier-Stokes equations is out of computational reach in the foreseeable future, and the need for better physical modeling is evident. Both cruise performance and stalling characteristics are influenced by strong interactions. Two important aspects of wing-flow physics are discussed: separation from a smooth surface that creates a vortex, and vortex bursting, the abrupt breakdown of a vortex with a subsequent loss of lift. Vortex aerodynamics of not-so-slender wings encounter particularly challenging problems, and it is shown how the design of early-generation operational aircraft surmounted these difficulties. Through use of forensic CFD, the article concludes with two case studies of aerodynamic design: how the Saab J29A wing maintains control authority near stall, and how the Saab J32 mitigates pitch-up instability at high incidence.
“…Numerical simulation of flight-test conditions using delayed detached-eddy simulation has been performed. Simulations at flight conditions using hybrid near-body/off body CFD have been carried out as well (Boelens et al 2009;Lofthouse and Cummings 2017;Morton et al 2017). Nevertheless, the application of the Q-criterion algorithm so far has not been combined with the footprint of the streamline for the vortex development, in order to scrutinize the complete picture of the vortex dynamics.…”
The choice for using a fighter fuselage in a fighter jet design affects a vortex generation advantageous in maneuverability. To study the effect of straight-body-type-fuselage (SBTF) on the vortex dynamic, a computational fluid dynamics (CFD) method is used, in order to simulate a model of SBTF fighter. The simulation uses Q-criterion to probe vortices, and a logarithmic grid to emphasize the micro-gridding effect of the turbulent boundary layer. The results show detailed quantitative velocity, pressure, trajectory of the vortex core, and wing negative surface pressure distribution (SPD), providing clear pictures of opportunity for performance improvement, better lift, agility, and maneuverability of a fighter if a model requires a new design.
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