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ASYMMETRIC TEMPORAL CROSS-CORRELATION FUNCTIONS IN TURBULENT SHEAR FLOWS

Bruno Eckhardt
Fachbereich Physik, Philipps-Universitat Marburg Renthof 6, D-35032 Marburg, Germany

Arne Jachens
Fachbereich Physik, Philipps-Universitat Marburg, D-35032 Marburg, Germany

Jorg Schumacher
Fachbereich Physik, Philipps-Universitat Marburg; Theoretical Fluid Mechanics, Department of Mechanical Engineering, Technische Universitat Ilmenau, P.O.Box 100565, D-98684 Ilmenau, Germany

Karsten Knobloch
Hermann-Fottinger-lnstitut fur Stromungsforschung, Technische Universitat, D-10623 Berlin, Germany

Hans H. Fernholz
Hermann-Fottinger-lnstitut fur Stromungsforschung, Technische Universitat, D-10623 Berlin, Germany

Abstract

Spatio-temporal cross-correlations between the turbulent velocity components in streamwise and wall-normal directions are investigated in an effort to identify effects due to non-normal amplification or lift up. The temporal cross-correlation between the downstream and normal velocity component shows a characteristic asymmetry related to the interplay between the streamwise streaks and pairs of streamwise vortices. Positive values of the asymmetry function Q > 0 implies that the shear flow is dominated by the no-normal lift-up of streamwise streaks by pairs of streamwise vortices. Q < 0 is found for regions in the shear flow where nonlinear convective effects dominate. This systematic variation of the asymmetry can be used to separate different layers in turbulent shear flows.