A regime of very long meandering positive and negative streamwise velocity fluctuations, that we term ‘superstructures’, are found to exist in the log lower wake regions turbulent boundary layers. Measurements made with a spanwise rake 10 hot-wires two separate facilities (spanning more than decade Re τ ) compared existing PIV DNS results. In all cases, note evidence large-scale stripiness fluctuations. The length these can commonly exceed 20δ. Similar scales have been previously reported...

In this paper we investigate the relationship between large- and small-scale energy-containing motions in wall turbulence. Recent studies a high-Reynolds-number turbulent boundary layer (Hutchins & Marusic, Phil. Trans. R. Soc. Lond . A, vol. 365, 2007 , pp. 647–664) have revealed possible influence of large-scale boundary-layer on near-wall cycle, akin to pure amplitude modulation. present study build upon these observations, using Hilbert transformation applied spectrally filtered...

Hot-wire data acquired in a high Reynolds number facility are used to illustrate the need for adequate scale separation when considering coherent structure wall-bounded turbulence. It is found that large-scale motion log region becomes increasingly comparable energy near-wall cycle as increases. Through decomposition of fluctuating velocity signals, it shown this has distinct modulating influence on small-scale (akin amplitude modulation). Reassessment DNS data, light these results, shows...

Careful reassessment of new and pre-existing data shows that recorded scatter in the hot-wire-measured near-wall peak viscous-scaled streamwise turbulence intensity is due large part to simultaneous competing effects Reynolds number wire length l + . An empirical expression given account for these effects. These factors can explain much disparity existing literature, particular explaining how previous studies have incorrectly concluded inner-scaled independent number. We also investigate...

The behavior of turbulent fluid motion, particularly in the thin chaotic layers immediately adjacent to solid boundaries, can be difficult understand or predict. These account for up 50% aerodynamic drag on modern airliners and occupy first 100 meters so atmosphere, thus governing wider meteorological phenomena. physics these is such that most important processes occur very close boundary--the region where accurate measurements simulations are challenging. We propose a mathematical model...

The extent or existence of similarities between fully developed turbulent pipes and channels, in zero-pressure-gradient boundary layers has come into question recent years. This is contrast to the traditionally accepted view that, upon appropriate normalization, all three flows can be regarded as same near-wall region. In this paper, authors aim provide clarification issue through streamwise velocity measurements these with carefully matched Reynolds number measurement resolution. Results...

Reliable full-scale prediction of drag due to rough wall-bounded turbulent fluid flow remains a challenge. Currently, the uncertainty is at least 10%, with consequences, for example, on energy and transport applications exceeding billions dollars per year. The crux difficulty large number relevant roughness topographies high cost testing each topography, but computational experimental advances in last decade or so have been lowering these barriers. In light advances, here we review...

The turbulent/non-turbulent interface in a zero-pressure-gradient turbulent boundary layer at high Reynolds number ( the streamwise/wall-normal plane with an unprecedented dynamic range. is detected using criteria of local kinetic energy and proves to be effective method for layers. presence superlayer corroborated by jump conditionally averaged streamwise velocity across interface. steep change accompanied discontinuity vorticity sharp rise shear stress. conditional statistics are...

Direct numerical simulations (DNS) are conducted for turbulent flow through pipes with three-dimensional sinusoidal roughnesses explicitly represented by body-conforming grids. The same viscous-scaled roughness geometry is first simulated at a range of different Reynolds numbers to investigate the effects low and $R_{0}/h$ , where $R_{0}$ pipe radius $h$ height. Results present class surfaces show that Hama function ${\rm\Delta}U^{+}$ only marginally affected (or ), observations outer-layer...

Abstract Despite its great scientific and technological importance, wall-bounded turbulence is an unresolved problem in classical physics that requires new perspectives to be tackled. One of the key strategies has been study interactions among energy-containing coherent structures flow. Such are explored this using explainable deep-learning method. The instantaneous velocity field obtained from a turbulent channel flow simulation used predict time through U-net architecture. Based on...

Stereoscopic particle image velocimetry (PIV) measurements are made in streamwise–spanwise and inclined cross-stream planes (inclined at plane, which is consistent with the presence of hairpin packets a low-speed region lifting away from wall.

A model is proposed with which the statistics of fluctuating streamwise velocity in inner region wall-bounded turbulent flows are predicted from a measured large-scale signature an outer position logarithmic flow. Results, including spectra and all moments up to sixth order, shown compared experimental data for zero-pressure-gradient over large range Reynolds numbers. The uses universal time-series constants that were empirically determined boundary layer data. In order test applicability...

This work can be viewed as a reprise of Head & Bandyopadhyay's (J. Fluid Mech. vol. 107, p. 297) original boundary-layer visualization study although in this instance we make use stereo particle image velocimetry (PIV), techniques to obtain quantitative view the turbulent structure. By arranging laser light-sheet and plane PIV system inclined spanwise/wall-normal planes (inclined at both plane, instantaneous swirl patterns exhibit predisposition for counter-rotating vortex pairs (arranged...

Abstract In this study we examine the impact of strength large-scale motions on amplitude and frequency small scales in high-Reynolds-number turbulent boundary layers. Time series hot-wire data are decomposed into large- small-scale components, large scale is considered. The modulation effect examined by conditionally averaging intensity ( ${ u}_{S}^{2} $ ) for various values fluctuation ${u}_{L} ). It shown that increases with increasing value near-wall region, whereas, farther away from...

An array of surface hot-film shear-stress sensors together with a traversing hot-wire probe is used to identify the conditional structure associated large-scale skin-friction event in high-Reynolds-number turbulent boundary layer. It found that events convect at velocity much faster than local mean near-wall region (the convection for fluctuations be close midpoint logarithmic region). Instantaneous data indicate presence structures wall are comparable scale and arrangement superstructure...

Abstract A model for the instantaneous wall-shear-stress distribution is presented zero-pressure-gradient turbulent boundary layers. The model, based on empirical and theoretical considerations, able to reconstruct a statistically representative fluctuating time-series, ${ \tau }_{w}^{\ensuremath{\prime} } (t)$ , using only low-frequency content of streamwise velocity measured in logarithmic region, away from wall. Results, including spectra second-order moments, show that capable...

Structural properties of regions uniform streamwise momentum in turbulent boundary layers are examined using experimental databases obtained from particle image velocimetry. This investigation employs a large range Reynolds numbers, spanning more than an order magnitude ( $Re_{{\it\tau}}=10^{3}{-}10^{4}$ ), enabling us to provide detailed description zones as function number. Our analysis starts by examining the identification criterion used Adrian et al. J. Fluid Mech. , vol. 422, 2000, pp....

Abstract A combination of cross-wire probes with an array flush-mounted skin-friction sensors are used to study the three-dimensional conditional organisation large-scale structures in a high-Reynolds-number turbulent boundary layer. Previous studies have documented amplitude modulation small-scale motions response conditionally averaged events, but data largely restricted streamwise component velocity alone. Here, we report results based on all three components and find that spanwise...

In this paper we study the spatial evolution of zero-pressure-gradient (ZPG) turbulent boundary layers from their origin to a canonical high-Reynolds-number state. A prime motivation is better understand under what conditions reliable scaling behaviour comparisons can be made between different experimental studies at matched local Reynolds numbers. This achieved here through detailed streamwise velocity measurements using hot wires in large University Melbourne wind tunnel. By keeping unit...

Turbulent boundary layer measurements above a smooth wall and sandpaper roughness are presented across wide range of friction Reynolds numbers, ${\it\delta}_{99}^{+}$ , equivalent sand grain $k_{s}^{+}$ (smooth wall: $2020\leqslant {\it\delta}_{99}^{+}\leqslant 21\,430$ rough $2890\leqslant 29\,900$ ; $22\leqslant k_{s}^{+}\leqslant 155$ $28\leqslant {\it\delta}_{99}^{+}/k_{s}^{+}\leqslant 199$ ). For the rough-wall measurements, mean shear stress is determined using floating element drag...

An inner-outer interaction model for predicting statistics of the near-wall streamwise velocity fluctuations via an input signal in log region is refined using linear spectral stochastic estimation. Velocity that are stochastically coherent between outer and inner processed with a scale-dependent gain phase during predictions.

Fully resolved measurements of turbulent boundary layers are reported for the Reynolds number range $Re_{\unicode[STIX]{x1D70F}}=6000{-}20\,000$ . Despite several decades research in wall-bounded turbulence there is still controversy over behaviour streamwise intensities near wall, especially at high numbers. Much it stems from uncertainty measurement due to finite spatial resolution. Conventional hot-wire anemometry limited resolution issues that cause attenuation intensity profile wall. To...