Phase-averaged waveforms of Reynolds stress in wall turbulence during the burst events of coherent structures

Abstract

The time sequence signals of instantaneous longitudinal and normal velocity components at different vertical locations in the turbulent boundary layer over a smooth flat plate have been finely measured by constant temperature anemometry of model IFA-300 and X-shaped hot-wire sensor probe in a wind tunnel. The longitudinal and normal velocity components have been decomposed into multi-scales by wavelet transform. The upward eject and downward sweep motions in a burst process of coherent structure have been detected by the maximum energy criterion of identifying burst event in wall turbulence through wavelet analysis. The relationships of phase-averaged waveforms among longitudinal velocity component, normal velocity component and Reynolds stress component have been studied through a correlation function method. The dynamics course of coherent structures and their effects on statistical characteristics of turbulent flows are analyzed. wall turbulence, coherent structure, burst, wavelet transform, Reynolds stress, phased-averaged waveformIn the early period of study, turbulent flow was deemed random and disordered motions of fluid particles. Since the 1940s, with the development of experimental technique of fluid mechanics, it became possible to do further and fine observation and measurement on the details of turbulent fluctuation. Relatively organized and intermittent large-scale motions were discovered in wake flows, jet flows, mixing layer and turbulent boundary layer [1,2] . The intensity, scale and structural form and shape of these large-scale motions are universal and repeated for the same kind of flow, so they are called coherent structures or organized structures [3] . In 1967, the flow-visualization study by Kline et al. [4] was a milestone of comprehensive and systemic study on important characteristics of the near-wall coherent structures. Corino [5] , Kim [6] and Smith [7] then analyzed the flow-visualization pictures both quantitatively and qualitatively. The following paraphrase their description of

Experimental investigation of Reynolds stress complex eddy viscosity model for coherent structure dynamics

“…In the present work, turbulent velocity signals will be decomposed into multiple-temporal-scale components by wavelet transform [13]. Wavelet transform (WT) is an effective mathematical technique widely used in the analysis of turbulent signals [14,15], and allows us to analyze a turbulent flow in terms of space and scale.…”

Effect of hydrophobicity on turbulent boundary layer under water

“…We can see that the ejection and sweep are the most important and typical processes of the bursting events. It has been proved that they contribute 60-80% of the Reynolds stress and form the main sources of the near-wall friction [35][36][37]. In this study, we use continuous wavelet transform (CWT) for the extraction and analysis of the bursting events.…”

Study on local topology model of low/high streak structures in wall-bounded turbulence by tomographic time-resolved particle image velocimetry

“…In the past half century, several methods have been proposed, e.g., the variable-interval time-averaging (VITA) scheme [17] , the quadrant splitting scheme [18] , the wavelet analysis [19] , and the linear stochastic estimation [20] . Jiang et al [21] and Liu et al [22] proposed the locally-averaged-structure function (LASF) to describe the local deformation and relative motion of the coherent structures. Yang and Jiang [23] extended the LASF to the 3D spatial flow field measured by the tomographic TRPIV, and identified the spatial topological mode of the coherent structures.…”