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What RDT tells us about T/NT interfaces

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The boundary layer separating a shear-free (no mean shear) isotropic turbulence region from an irrotational (or non-turbulent) flow region is investigated using rapid distortion theory (RDT), assuming that the turbulent/non-turbulent (T/NT) interface is suddenly inserted and remains approximately flat. When only inviscid processes are taken into account, the values taken at the T/NT interface by turbulence statistics, like the TKE and the dissipation rate ε, do not depend on the form of the turbulence energy spectrum. The dissipation rate decays like z−6 in the irrotational flow region. When viscous effects are taken into account, the agreement of various turbulence statistics with DNS data is found to be very good. ε displays a large maximum at the T/NT interface, which can be quantitatively related to the thickness of the viscous boundary layer (VBL). For an equilibrium VBL, RDT suggests that the T/NT interface thickness scales with the Kolmogorov microscale.

Author(s):

Miguel Teixeira    
University of Reading
United Kingdom

Carlos Silva    
Technical University of Lisbon
Portugal