Extension of d’Alembert’s Paradox for Elongated Bodies and A Curious Theoretical Prediction for Turbulent Ducts
Speaker: Philippe Spalart, The Boeing Company
Presentation
Seminar Slide Deck (PDF-5.5MB)
Abstract
In Part A, Extension of d’Alembert’s Paradox for Elongated Bodies, it is first recalled that the paradox applies to the entire force vector, and not only the drag. Then, a new theorem is presented showing that for elongated bodies such as trains, at zero angle of attack, the forces on the nose and tail are shape-independent and are zero separately, rather than canceling each other. This is an asymptotic result. A consequence is that, in simple words, there is no way to reduce drag by re-designing the nose. In Part B, A Curious Theoretical Prediction for Turbulent Ducts, it is shown that the application of the law of the wall and defect law to non-circular ducts, such as elliptical ones, leads to the unexpected prediction that the skin friction is uniform around the perimeter. RANS results agree with this, asymptotically at high Reynolds numbers, and DNS results are supportive of the property.
Biography
Philippe Spalart studied Mathematics and Engineering in Paris, and obtained an Aerospace Ph.D. at Stanford through NASA Ames Research Center in 1982. While at Ames, he conducted extensive Direct Numerical Simulations of transitional and turbulent boundary layers. After moving to Boeing in 1990, he created the Spalart-Allmaras (SA) one-equation Reynolds-Averaged Navier-Stokes turbulence model. He wrote a review (once described as “discerning and sobering”) and co-holds a patent on airplane trailing vortices. In 1997, he proposed the Detached-Eddy Simulation approach, blending RANS and Large-Eddy Simulation to address separated flows at high Reynolds numbers with a manageable cost. Recent work includes refinements to the SA model, computational aeroacoustics, and theories for aerodynamics and turbulence.