Streamwise evolution of longitudinal vortices in a turbulent boundary layer
2009 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 623, 27-58 p.Article in journal (Refereed) Published
In this experimental study both smoke visualisation and three component hotwire measurements have been performed in order to characterize the streamwise evolution of longitudinal counter-rotating vortices in a turbulent boundary layer. The vortices were generated by means of vortex generators (VGs) in different configurations. Both single pairs and arrays in a natural setting as well as in yaw have been considered. Moreover three different vortex blade heights h, with the spacing d and the distance to the neighbouring vortex pair D for the array con guration, were studied keeping the same d / h and D / h ratios. It is shown that the vortex core paths scale with h in the streamwise direction and with D and h in the spanwise and wall-normal directions, respectively. A new peculiar "hooklike" vortex core motion, seen in the cross-ow plane, has been identi ed in the far region, starting around 200h and 50h for the pair and the array con guration, respectively. This behaviour is explained in the paper. Furthermore the experimental data indicate that the vortex paths asymptote to a prescribed location in the cross-ow plane, which rst was stated as a hypothesis and later veri ed. This observation goes against previously reported numerical results based on inviscid theory. An account for the important viscous e ects is taken in a pseudo-viscous vortex model which is able to capture the streamwise core evolution throughout the measurement region down to 450h. Finally, the e ect of yawing is reported, and it is shown that spanwiseaveraged quantities such as the shape factor and the circulation are hardly perceptible. However, the evolution of the vortex cores are di erent both between the pair and the array con guration and in the natural setting versus the case with yaw. From a general point of view the present paper reports on fundamental results concerning the vortex evolution in a fully developed turbulent boundary layer.
Place, publisher, year, edition, pages
2009. Vol. 623, 27-58 p.
Array configurations; Counter-rotating vortices; Cross flows; Experimental data; Experimental studies; Hot-wire measurements; Inviscid theory; Longitudinal vortices; Numerical results; Shape factor; Smoke visualization; Streamwise directions; Three-component; Turbulent boundary layers; Viscous effect; Vortex cores; Vortex generators; Vortex model; Vortex pair; Vortex paths; Wall-normal direction
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-9835DOI: 10.1017/S0022112008004825ISI: 000264507000002ScopusID: 2-s2.0-65649153763OAI: oai:DiVA.org:kth-9835DiVA: diva2:133505
QC 20100825. Uppdaterad från accepted till published (20100825).2009-01-122009-01-122010-08-25Bibliographically approved