The local and global stability of confined planar wakes at intermediate Reynolds number
2011 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 686, 218-238 p.Article in journal (Refereed) Published
At high Reynolds numbers, wake flows become more globally unstable whenconfined within a duct or between two flat plates. At Reynolds numbers around100, however, global analyses suggest that such flows become more stable whenconfined, while local analyses suggest that they become more unstable. Theaim of this paper is to resolve this apparent contradiction. In this theoreticaland numerical study, we combine global and local stability analyses of planarwake flows at Re = 100 to determine the effect of confinement. We find thatconfinement acts in three ways: it modifies the length of the recirculation zoneif one exists, it brings the boundary layers closer to the shear layers, and itcan make the flow more locally absolutely unstable. Depending on the flowparameters, these effects work with or against each other to destabilize orstabilize the flow. In wake flows at Re = 100 with free slip boundaries, flowsare most globally unstable when the outer flows are 50% wider than the halfwidthof the inner flow because the first and third effects work together. Inwake flows at Re = 100 with no slip boundaries, confinement has little overalleffect when the flows are weakly confined because the first two effects workagainst the third. Confinement has a strong stabilizing effect, however, whenthe flows are strongly confined because all three effects work together. Bycombining local and global analyses, we have been able to isolate these threeeffects and resolve the apparent contradictions in previous work.1.
Place, publisher, year, edition, pages
2011. Vol. 686, 218-238 p.
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-34144DOI: 10.1017/jfm.2011.324ISI: 000297295900009ScopusID: 2-s2.0-84855508019OAI: oai:DiVA.org:kth-34144DiVA: diva2:419295