Experimental investigation of vortex properties in a turbulent boundary layer

Abstract

Dual-plane particle image velocimetry experiments were performed in a turbulent boundary layer with Re = 1160 to obtain all components of the velocity gradient tensor. Wall-normal locations in the logarithmic and wake region were examined. The availability of the complete gradient tensor facilitates improved identification of vortex cores and determination of their orientation and size. Inclination angles of vortex cores were computed using statistical tools such as two-point correlations and joint probability density functions. Also, a vortex identification technique was employed to identify individual cores and to compute inclination angles directly from instantaneous fields. The results reveal broad distributions of inclination angles at both locations. The results are consistent with the presence of many hairpin vortices which are most frequently inclined downstream at an angle of 45 ‫ؠ‬ with the wall. According to the probability density functions, a relatively small percentage of cores are inclined upstream. The number density of forward leaning cores decreases from the logarithmic to the outer region while the number density of backward-leaning cores remains relatively constant. These trends, together with the correlation statistics, suggest that the backward-leaning cores are part of smaller, weaker structures that have been distorted and convected by larger, predominantly forward-leaning eddies associated with the local shear.

Interactions within the turbulent boundary layer at high Reynolds number

“…Theodorsen 1952;Acarlar & Smith 1987;Adrian et al 2000;Ganapathisubramani, Longmire & Marusic 2003;Ganapathisubramani, Longmire & Marusic 2006). They are perhaps the prototypical example of eddies that are attached to the wall.…”

Geometric study of Lagrangian and Eulerian structures in turbulent channel flow

“…Some appear to form complete or incomplete hairpin-or Λ-like structures. Similar observations were also made by Adrian & Liu (2002) and Ganapathisubramani et al (2006). After interpolating λ ci on a uniform grid with resolution 2N x × N y × N z , the multiscale and multi-directional methodology described in § 3 is applied on a sequence of λ ci -fields on the x-y or x-z planes.…”

“…Using PIV experiments and statistical tools Ganapathisubramani, Longmire & Marusic (2006) identified individual vortex cores most frequently inclined at 45…”

Characterization of Near-Wall Turbulent Flows by Tomographic Piv

“…153 6.34 Ejection and sweep detection procedure in the the middle plane of the tomo-PIV data: (a) colorplot of .65 Probability density function of projection angle on the streamwise-wall-normal plane for [Honkan and Andreopoulos, 1997] and vortex conditional statistics of tomo-PIV data. 181 6.66 Probability density function of elevation angle of unfiltered and filtered vortices detected on the streamwise-spanwise PIV plane at y + = 110 (adapted from figure 7 of [Ganapathisubramani et al, 2006]). The axis of the transfer function (TF) reads on the right.…”

“…• downstream ( [Theodorsen, 1952, Robinson, 1991a, Adrian, 1991, Robinson, 1991a, Ganapathisubramani et al, 2006), due to the stretching of the mean velocity gradient and to the mechanism of self-induction which lifts them up. Hairpin (or horseshoe) vortices are the major momentum-transporting structures in shear turbulence ( [Theodorsen, 1952]).…”