The Delay of RANS-to-LES Transition in Hybrid RANS-LES Approaches and Some Recently Proposed Remedies
The possibility of a crucial delay in the transition from RANS to LES in free and separated shear layers within hybrid RANS-LES methods was anticipated, starting in the proposal of Detached-Eddy Simulation in 1997. Its origin (the presence of the so called “grey area” in the vicinity of the RANS-LES interface) is well understood, but despite numerous attempts to resolve this issue within zonal and, especially, within non-zonal RANS-LES hybrids, this objective has not been achieved. Moreover, a perfect solution can hardly be expected, since the presence of the “grey area” is a fundamental obstacle in seamless hybrid methods, and in fact in many versions of LES. Nonetheless, during the last few years significant progress in this direction has been made, and some effective remedies allowing a significant shortening of the grey area have been proposed. In this lecture, we outline some of the remedies proposed recently by the authors and illustrate their efficiency in terms of both aerodynamics and aeroacoustics by a set of numerical examples including canonical flows with free and separated shear layers and some more complex flows (round subsonic jet and airfoil with flap).
KeywordsShear Layer Separate Shear Layer Detach Eddy Simulation Free Shear Layer Vorticity Vector
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