Coherent motions in the outer region of turbulent boundary layers

Abstract

The technique of simultaneous hot-wire anemometry and flow visualization has been used to determine the average characteristics of two important scales of motion in the outer region of turbulent boundary layers: large scale motions (average length 1.6δ), and ’’typical eddy’’ motions (average streamwise length approximately 200 ν/uτ). Results showed that the Reynolds number dependent ’’typical eddies’’ produced most of the Reynolds stress in the outer half of the layer at Rϑ≈1200, and that they are formed on the upstream side of large scale motions at all Reynolds numbers investigated. This phase relationship explains the scaling of the frequency of occurrence of outer layer bursts (which are identified with ’’typical eddies’’) on the free stream velocity and overall boundary layer thickness, although it is found that the lengths of the ’’typical eddies’’ scale on inner layer variables. In the log region, roughly one-half of the large scale motions sampled had zone-averaged streamwise velocity defects. Ensemble averaged results showed that they were associated with significant Reynolds stress contributions. A structural model showing the phase relationship of ’’typical eddies’’ and large scale motions is presented.

Visualization Study of Turbulent Spots.

“…Similar conclusions have been drawn by Falco (1977) for a fully developed turbulent boundary layer at moderate Reynolds numbers.…”

“…In the movie frames from which other. In fact, the interior of both spots at all spanwise locations resembled a turbulent boundary layer (Falco;1977). The eddies slowly grew and moved away from the plate, providing the growth in the normal direction.…”

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

“…The phase information of turbulent fields therefore should be included in the eddy viscosity model. This proposal has been confirmed by the numerical simulations of Wu [2], Luo [5,8] and experimental measurements of Falco [4], Bruns [9], Wang [10], Li [11] and Guo [12]. However, the theoretical model of CS still needs to be further investigated to gain more detailed information in the different regions of the whole TBL.…”

“…(10) in the two-dimensional form is expressed as: [2] adopted the constant CEVM, but the eigenfunction showed an oscillatory behavior, which was inconsistent with Brown's experimental results [3]. Falco et al [4] presented a structural model of 'typical eddy' formed on the upstream of large scale motions, and found there was a phase relationship between 'typical eddies' producing most of the Reynolds stress and large scale motions associated with significant Reynolds stress contributions. Luo et al [5] suggested a CEVM model based on the numerical simulation to explain large scale CS in the outer region of turbulent boundary layer (TBL).…”

Three-dimensional vortex organization in a high-Reynolds-number supersonic turbulent boundary layer

“…Falco 1977). More recently, it was realized that hairpin vortices are in turn organized into packets (Adrian, Meinhart & Tomkins 2000;Christensen & Adrian 2001), which can be thought of as a streamwise train of hairpins.…”