Ellen K. Longmire

Characteristics of vortex packets in turbulent boundary layers

Stereoscopic particle image velocimetry (PIV) was used to measure all three instantaneous components of the velocity field in streamwise–spanwise planes of a turbulent boundary layer at Re τ =1060 ( Re θ =2500). Datasets were obtained in the logarithmic layer and beyond. The vector fields in the log layer ( z + =92 and 150) revealed signatures of vortex packets similar to those proposed by Adrian and co-workers in their PIV experiments. Groups of legs of hairpin vortices appeared to be coherently arranged in the streamwise direction. These regions also generated substantial Reynolds shear stress, sometimes as high as 40 times − uw . A feature extraction algorithm was developed to automate the identification and characterization of these packets of hairpin vortices. Identified patches contributed 28% to − uw while occupying only 4% of the total area at z + =92. At z + =150, these patches occupied 4.5% of the total area while contributing 25% to − uw . Beyond the log layer ( z + =198 and 530), the spatial organization into packets is seen to break down.

Investigation of large-scale coherence in a turbulent boundary layer using two-point correlations

Stereoscopic particle image velocimetry (PIV) measurements are made in streamwise–spanwise and inclined cross-stream planes (inclined at

Drop coalescence through a liquid/liquid interface

45^\circ

Experimental investigation of vortex properties in a turbulent boundary layer

and

Effectively visualizing multi-valued flow data using color and texture

135^\circ

Bifurcating jets generated with stepped and sawtooth nozzles

to the principal flow direction) of a turbulent boundary layer at moderate Reynolds number (

Particle image velocimetry in a variable density flow: application to a dynamically evolving microburst

\hbox{\it Re}_\tau\,{\sim} 1100

VORTEX DYNAMICS IN JETS FROM INCLINED NOZZLES

). Two-point spatial velocity correlations computed using the PIV data reveal results that are consistent with an earlier study in which packets of hairpin vortices were identified by a feature-detection algorithm in the log region, but not in the outer wake region. Both streamwise–streamwise (

Dynamics of experimentally simulated microbursts

R_{\hbox{\scriptsize\it uu}}

Vortex rings from cylinders with inclined exits

) and streamwise–wall-normal (