Wall-Normal Variation of Spanwise Streak Spacing in Turbulent Boundary Layer With Low-to-Moderate Reynolds Number

Abstract

Low-speed streaks in wall-bounded turbulence are the dominant structures in the near-wall turbulent self-sustaining cycle. Existing studies have well characterized their spanwise spacing in the buffer layer and below. Recent studies suggested the existence of these small-scale structures in the higher layer where large-scale structures usually receive more attention. The present study is thus devoted to extending the understanding of the streak spacing to the log layer. An analysis is taken on two-dimensional (2D) wall-parallel velocity fields in a smooth-wall turbulent boundary layer with Ret = 4402400, obtained via either 2D Particle Image Velocimetry (PIV) measurement taken here or public Direct Numerical Simulation (DNS). Morphological-based streak identification analysis yields a Re-independent log-normal distribution of the streak spacing till the upper bound of the log layer, based on which an empirical model is proposed to account for its wall-normal growth. The small-scale part of the spanwise spectra of the streamwise fluctuating velocity below y? = 100 is reasonably restored by a synthetic simulation that distributes elementary streak units based on the proposed empirical streak spacing model, which highlights the physical significance of streaks in shaping the small-scale part of the velocity spectra beyond the buffer layer.

Transport of Turbulence Across Permeable Interface in a Turbulent Channel Flow: Interface-Resolved Direct Numerical Simulation

“…The spanwise spectra of cases A1 and A2 show basically identical pattern on the permeable and non-permeable side, with inner peaks at t+ z ≈ 100 ( z ∕D ≈ 1 for case A1 and 0.5 for case A2). This is consistent with the value of a canonical wall-bounded flow (Wang et al 2019a). In contrast, cases B1 and B2 biased from the spectra of a wall-bounded flow, with a considerable portion of energy residing at large scale modes z ∕D ≥ 5 .…”

“…The purpose is to find the physical links between the geometrical feature of the porous media and the characteristics of the turbulence transfer process at the permeable interface, which helps the design of porous structures that generate specific flow properties. The turbulent statistics acquired here can be also used to support different levels of modeling like large-eddy-simulation (LES), Reynolds-averaged-Navier-Stokes (RANS) (Weihaupt et al 2019;Yang et al 2018Yang et al , 2019 modelling or modal-based reduced order modeling (Wang et al 2018(Wang et al , 2019a(Wang et al , 2019b. In the following, Sect.…”

Wake-induced transition in the low-Reynolds-number flow over a multi-element airfoil

“…The R profiles are further extracted from the reference positions in figure 20 and shown in figure 21 for the determination of spanwise wavelengths. As revealed in Wang, Pan & Wang (2019), the spanwise wavelengths of related flow patterns are defined as the distances between the minima of R profiles (marked by red crosses in figure 21). The spanwise wavelength of the Λ vortices couples with that of the disturbances in the slat wake at each Re c (table 2).…”

Intermittency and Self-Organisation in Turbulence and Statistical Mechanics

“…Experimentally, as an example of self-pulsing spatially extended systems, they consider vertical-cavity surface emitting lasers with an integrated saturable absorber and study the complex dynamics and extreme events accompanied by spatiotemporal chaos. Theoretically, by employing the Ginzburg-Landau model, they characterize intermittency by the Lyapunov spectrum and Kaplan-Yorke dimension and show the chaotic alternation of phase and amplitude turbulence, extreme events induced by the alternation of defects and phase turbulence.Wang et al [8] investigate the effect of streaks (structures) on wall-bounded turbulence at low-to-moderate Reynolds number by using 2D Particle Image Velocimetry measurement and direct numerical simulations. To understand the spanwise spacing of neighbouring streaks, they present a morphological streak identification analysis and discuss wall-normal variation of the streak spacing distributions, fitting by log-normal distributions, and Re-(in)dependence.…”

“…Wang et al [8] investigate the effect of streaks (structures) on wall-bounded turbulence at low-to-moderate Reynolds number by using 2D Particle Image Velocimetry measurement and direct numerical simulations. To understand the spanwise spacing of neighbouring streaks, they present a morphological streak identification analysis and discuss wall-normal variation of the streak spacing distributions, fitting by log-normal distributions, and Re-(in)dependence.…”