Changes in flight stability characteristics at the advanced stage of aircraft design are complex and require thorough investigations. This paper examines the impact of wing strake modification on high-performance aircraft using computational fluid dynamics (CFD). The dynamic behaviour is calculated using the forced oscillation technique, while the effect of geometric variation on longitudinal stability characteristics is extensively studied. Steady-state experimental data is utilised to validate the computational setup. Static aerodynamic coefficients, dynamic stability derivatives and the positions of aerodynamic and pressure centres are employed to quantify the changes. Furthermore, the alterations in stability characteristics are correlated with flow physics. The results indicate a reduction in longitudinal static and dynamic stability at various flight conditions due to the proposed modification. This deliberate reduction was necessary to accommodate the installation of a fly-by-wire system. The discussed design changes have been effectively implemented on an in-service aircraft.

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.

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.

Fluid flow phenomena are very closely related to the casting quality and surface finish of the cast part. In addition, the good quality of the casting product can be achieved by using an optimum gating system design. In this work, a vortex well, which is one of the important components of gating system design, is utilized in order to demonstrate its effectiveness in improving the mechanical and microstructure properties of the cast part. An X-ray radiography test was performed in order to investigate the porosity distribution in castings with different vortex well dimensions. The scatter of flexure strength results was quantified by Weibull statistics. Microstructure analysis was conducted by using a scanning electron microscope (SEM) to examine the microstructure of selected casting specimens produced from the vortex well design. By optimizing the vortex well design, porosity inside the casting was significantly reduced, while the mechanical strength and reliability of aluminum casting were further enhanced.