Fine Structure of Reynolds Shear Stress in an Unsteady Turbulent Channel Flow
The modulation characteristics of the Reynolds shear stresses in an unsteady channel flow are presented. The imposed frequency covers a large range going from the quasi-steady limit to 2 times the ejection frequency at y + = 15. The time mean contributions of the quadrants to the Reynolds shear stress are unaffected by the imposed unsteadiness. The contributions of the second and fourth quadrants are strongly modulated near the imposed frequency in wall units f + ≈ 0.002, where the modulation of the ejection frequency is weak and the phase shift with respect to the centerline velocity is maximum. In the low frequency regime the ejection frequency is modulated as the wall shear stress according to the quasi-steady behaviour, and the decline in its response in the high imposed frequency regime stretches from the near-wall to the outer layer.
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