Abstract

Instantaneous wall-shear-stress fluctuations contribute to drag associated with an increase in frictional Reynolds number Reτ [1]. Wall-pressure fluctuations are known to couple with structural modes and induce vibrations in engineering applications. The footprint of very large-scale motions (VLSMs) centred in the logarithmic region [2] on the near-wall turbulence becomes increasingly energetic with increasing Reτ . While the characteristics of the VLS Ms themselves have been explored in detail in recent years, their signature on the wall has been less well documented and has yet to be incorporated into, for example, acoustic models. In this study, we explore the origins of subconvective wall-shear stress and pressure fluctuations in a channel flow at Reτ = 550 (Fig. 1) and use data-driven techniques to identify the influence of VLS Ms. Our approach uses snapshots in wavespeed space above (faster than) the convective ridge to identify the so-called subconvective components of the flow. Consideration of the Fourier transformed advection term allows us to identify the most relevant permitted triad pairs in the subconvective regime for both the wall-pressure and shear-stress fluctuations. We further decompose pressure fluctuations into fast, slow, and Stokes components to elucidate their distinct roles in subconvective dynamics. Our findings will underpin the development of predictive models that account for the subconvective components of wall-bounded turbulence at high Reynolds number, which may be used for flow control and noise reduction in engineering applications.

References [1] Koji Fukagata, Kaoru Iwamoto, and Nobuhide Kasagi. Contribution of Reynolds stress distribution to the skin friction in wall-bounded flows. Physics of Fluids, 2002. [2] Nicholas Hutchins and Ivan Marusic. Evidence of very long meandering features in the logarithmic region of turbulent boundary layers. Journal of Fluid Mechanics, 579:1–28, 2007.