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DNS of laminar separation nubble flows with free‐stream fluctuations
Author(s) -
Wissink Jan G.,
Rodi Wolfgang
Publication year - 2007
Publication title -
pamm
Language(s) - English
Resource type - Journals
ISSN - 1617-7061
DOI - 10.1002/pamm.200700436
Subject(s) - turbulence , laminar flow , mechanics , instability , oscillation (cell signaling) , physics , bubble , direct numerical simulation , amplitude , inflow , chemistry , optics , reynolds number , biochemistry
Abstract A series of Direct Numerical Simulations (DNS) of Laminar Separation Bubble (LSB) flow in the presence of external disturbances has been performed. In all simulations, the primary mechanism for the transition to turbulence was found to be a two‐dimensional Kelvin‐Helmholtz (KH) instability of the separated shear layer that was triggered by the external fluctuation(s). The KH instability caused the shear layer to roll up. Inside the rolled up shear layer, entrained disturbances triggered elliptic instabilities which led to a rapid transition to fully three‐dimensional (3D) turbulence. In the simulations with inflow oscillations the streamwise variation of the location of transition was found to decrease with the amplitude of the inflow oscillation. In the simulations with free‐stream turbulence the size of the separation bubble – measured by the shape factor – was found to drastically decrease with increasing free‐stream turbulence level. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)