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The Mission and Requirements of a Turbulence Model

AMS Seminar Series

Speaker: Philippe Spalart, The Boeing Company

Presentation

Seminar Slide Deck (PDF-9.9MB)

Abstract

"The Mission" half of the talk will first argue that a model should be essentially universal, considering that a single flow field can contain many deeply different flow modules. It needs to be well-posed mathematically. The differential equations and boundary conditions must be absolutely complete. Its physical rationale is desirable, as is version control with full clarity. "The Requirements" half could serve a purpose in the era of Machine Learning (ML), which brings in colleagues with little “turbulence culture.” This has led unfortunately to many ML products failing some very basic requirements, which are self-evident to the experienced modelers but deserve a clear exposition. In particular, a list is given and justified for “features” which must be avoided when creating a new model. The argument over the use of acceleration (pressure gradient) is salient. The talk concludes with thoughts about effective community turbulence research, especially seeking a good use of Artificial Intelligence.

Biography

Photo of Philippe Spalart
Philippe Spalart studied Mathematics and Engineering in Paris, and obtained an Aerospace Ph.D. at Stanford/NASA-Ames in 1982. Still at Ames, he conducted extensive Direct Numerical Simulations of transitional and turbulent boundary layers. Moving to Boeing in 1990, he created the Spalart-Allmaras 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. He was elected to the National Academy of Engineering in 2017. Recent work includes refinements to the SA model and DES, computational aeroacoustics, theories for aerodynamics and turbulence, and the design of research experiments.