Dns of the Generation of Secondary -vortices in a Transitional Boundary Layer

Especially for large amplitude initial disturbances so called vortices de velop during the non linear late stages of laminar turbulent transition Once formed they may persist as so called hairpin vortices well into the ensuing turbulent boundary layer This makes their study important for under standing transition and turbulence in wall bounded shear ows In Direct Numerical Simulations DNS as well as in controlled tran sition experiments especially in K type transition vortices have been regularly observed by all authors studying this phenomenon In such ex periments or DNS vortices may be generated periodically in time and in spanwise direction by the non linear interaction of a large amplitude Tollmien Schlichting TS wave with a spatially periodic steady modula tion in spanwise direction with a certain wavelength z z In the present paper we shall demonstrate the in uence of increasing z with the idea of moving spanwise adjacent vortices further apart in order to identify their possible self interaction in the original case where z z